File Coverage

blib/lib/Geo/BUFR.pm

Criterion	Covered	Total	%
statement	2437	2905	83.8
branch	1211	1942	62.3
condition	380	693	54.8
subroutine	127	147	86.3
pod	0	94	0.0
total	4155	5781	71.8

package Geo::BUFR;

# Copyright (C) 2010-2025 MET Norway
#
# This module is free software; you can redistribute it and/or
# modify it under the same terms as Perl itself.

=begin General_remarks

Some general remarks on variables
---------------------------------

@data = data array
@desc = descriptor array

These 2 arrays are in one to one correspondence, but note that some C
descriptors (2.....) are included in @desc even though there is no
associated data value in message (the corresponding element in @data
is set to ''). These descriptors without value are printed in
dumpsection4 without line number, to distinguish them from 'real' data
descriptors.

$idesc = index of descriptor in @desc (and @data)
$bm_idesc = index of bit mapped descriptor in @data (and @desc, see below)

Variables related to bit maps:

$self->{BUILD_BITMAP}
$self->{BITMAP_INDEX}
$self->{NUM_BITMAPS}
$self->{BACKWARD_DATA_REFERENCE}

These are explained in sub new

$self->{BITMAP_OPERATORS}

Reference to an array containing operators in BUFR table C which are
associated with bit maps, i.e. one of 22[2-5]000 and 232000; the
operator being added when it is met in section 3 in message. Note that
an operator may occur multiple times, which is why we have to use an
array, not a hash.

$self->{CURRENT_BITMAP}

Reference to an array which contains the indexes of data values for
which data is marked as present in 031031 in the current used bit map.
E.g. [2,3,6] if bitmap = 1100110.

$self->{BITMAP_START}

Array containing for each bit map the index of the first element
descriptor for which the bit map relates.

$self->{BITMAPS}

Reference to an array, one element added for each bit map operator in
$self->{BITMAP_OPERATORS} and each subset (although for compression we
assume all subset have identical bitmaps and operate with subset 0
only, i.e. $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[0] instead of
...->[$isub]), the element being a reference to an array containing
consecutive pairs of indexes ($idesc, $bm_idesc), used to look up in
@data and @desc arrays for the value/descriptor and corresponding bit
mapped value/descriptor.

$self->{REUSE_BITMAP}

Gets defined when 237000 is met, undefined if 237255 or 235000 is met.
Originally for each subset (but defined for subset 0 only if
compression) set to reference an array of the indexes of data values
to which the last used bitmap relates (fetched from $self->{BITMAPS}),
then shifted as the new element in $self->{BITMAPS} is built up.

For operator 222000 ('Quality information follows') the bit mapped
descriptor should be a 033-descriptor. For 22[3-5]/232 the bit mapped
value should be the data value of the 22[3-5]255/232255 descriptors
following the operator in BUFR section 3, with bit mapped descriptor
$desc[bm_idesc] equal to $desc[$idesc] (with data width and reference
value changed for 225255)

=end General_remarks

=cut

require 5.006;
use strict;
use warnings;
use Carp;
use Cwd qw(getcwd);
use FileHandle;
use File::Spec::Functions qw(catfile);
use Scalar::Util qw(looks_like_number);
use Time::Local qw(timegm);
# Also requires Storable if sub copy_from() is called

require DynaLoader;
our @ISA = qw(DynaLoader);
our $VERSION = '1.41';

# This loads BUFR.so, the compiled version of BUFR.xs, which
# contains bitstream2dec, bitstream2ascii, dec2bitstream,
# ascii2bitstream and null2bitstream
bootstrap Geo::BUFR $VERSION;


# Some package globals
our $Verbose = 0;

# $Verbose or $self->{VERBOSE} > 0 leads to the following output, all
# except for level 6 on lines starting with 'BUFR.pm: ':
# 1 -> B,C,D tables used (full path)
# 2 -> Identifying stages of processing, displaying length of sections
#      and some additional data from section 1 and 3
# 3 -> All descriptors and values extracted
# 4 -> Operator specific information, including delayed replication
#      and repetition
# 5 -> BUFR compression specific information
# 6 -> Calling dumpsection0,1,3

our $Spew = 0; # To avoid the overhead of subroutine calls to _spew
               # (which is called a lot), $Spew is set to 1 if global
               # $Verbose or at least one object VERBOSE is set > 1.
               # This should speed up execution a bit in the common
               # situation when no verbose output (except possibly
               # the BUFR tables used) is requested
our $Nodata = 0; # If set to true will prevent decoding of section 4
our $Noqc = 0; # If set to true will prevent decoding (or encoding) of
               # any descriptors after 222000 is met
our $Reuse_current_ahl = 0;
               # If set to true will cause cet_current_ahl() to return
               # last AHL extracted and not undef if currently
               # processed BUFR message has no (immediately preceding)
               # AHL
our $Strict_checking = 0; # Ignore recoverable errors in BUFR format
                          # met during decoding. User might set
                          # $Strict_checking to 1: Issue warning
                          # (carp) but continue decoding, or to 2:
                          # Croak instead of carp

# The next 2 operators are separated for readability. Public interface should
# provide only set_show_all_operators() to set both of these (to the same value)
our $Show_all_operators = 0; # = 0: show just the most informative C operators in dumpsection4
                             # = 1: show all operators (as far as possible)
our $Show_replication = 0; # = 0: don't include replication descriptors (F=1) in dumpsection4
                           # = 1: include replication descriptors(F=1) in dumpsection4,
                           #  with X in FXY replaced with actual number X' of replicated descriptors.
                           #  X' is replaced by 0 if X' > 99

our %BUFR_table;
# Keys: PATH      -> full path to the chosen directory of BUFR tables
#       FORMAT    -> supported formats are BUFRDC and ECCODES
#       B$version -> hash containing the B table $BUFR_table/B$version
#                    key: element descriptor (6 digits)
#                    value: a \0 separated string containing the B table fields
#                            $name, $unit, $scale, $refval, $bits
#       C$version -> hash containing the C table $BUFR_table/C$version
#                    key: table B descriptor (6 digits) of the code/flag table
#                    value: a new hash, with keys the possible values listed in
#                           the code table, the value the corresponding text
#       D$version -> hash containing the D table $BUFR_table/D$version
#                    key: sequence descriptor
#                    value: a space separated string containing the element
#                    descriptors (6 digits) the sequence descriptor expands to
$BUFR_table{FORMAT} = 'BUFRDC'; # Default. Might in the future be changed to ECCODES

our %Descriptors_already_expanded;
# Keys: Text string "$table_version $unexpanded_descriptors"
# Values: Space separated string of expanded descriptors

sub _croak {
    my $msg = shift;
    croak "BUFR.pm ERROR: $msg";
}

## Carp or croak (or ignore) according to value of $Strict_checking
sub _complain {
    my $msg = shift;
    if ($Strict_checking == 1) {
        carp "BUFR.pm WARNING: $msg";
    } elsif ($Strict_checking > 1) {
        croak "BUFR.pm ERROR: $msg";
    }
    return;
}

sub _spew {
    my $self = shift;
    my $level = shift;
    if (ref($self)) {
        # Global $Verbose overrides object VERBOSE
        return if $level > $self->{VERBOSE} && $level > $Verbose;
    } else {
        return if $level > $Verbose;
    }
    my $format = shift;
    if (@_) {
        printf "BUFR.pm: $format\n", @_;
    } else {
        print "BUFR.pm: $format\n";
    }
    return;
}

## Object constructor
sub new {
    my $class = shift;
    my $self = {};
    $self->{VERBOSE} = 0;
    $self->{CURRENT_MESSAGE} = 0;
    $self->{CURRENT_SUBSET} = 0;
    $self->{BUILD_BITMAP} = 0; # Will be set to 1 if a bit map needs to
                               # be built
    $self->{BITMAP_INDEX} = 0; # Used for building up bit maps; will
                               # be incremented for each 031031
                               # encountered, then reset to 0 when bit
                               # map is finished built
    $self->{NUM_BITMAPS} = 0;  # Will be incremented each time an
                               # operator descriptor which uses a bit
                               # map is encountered in section 3
    $self->{BACKWARD_DATA_REFERENCE} = 1; # Number the first bitmap in
                               # a possible sequence of bitmaps which
                               # relate to the same scope of data
                               # descriptors. Starts as 1 when (or
                               # rather before) the first bitmap is
                               # constructed, will then be reset to
                               # the number of the next bitmap to be
                               # constructed each time 235000 is met
    $self->{NUM_CHANGE_OPERATORS} = 0; # Will be incremented for
                               # each of the operators CHANGE_WIDTH,
                               # CHANGE_CCITTIA5_WIDTH, CHANGE_SCALE,
                               # CHANGE_REFERENCE_VALUE (actually
                               # NEW_REFVAL_OF), CHANGE_SRW and
                               # DIFFERENCE_STATISTICAL_VALUE in effect

    # If number of arguments is odd, first argument is expected to be
    # a string containing the BUFR message(s)
    if (@_ % 2) {
        $self->{IN_BUFFER} = shift;
    }

    # This part is not documented in the POD. Better to remove it?
    while (@_) {
        my $parameter = shift;
        my $value = shift;
        $self->{$parameter} = $value;
    }
    bless $self, ref($class) || $class;
    return $self;
}

## Copy contents of the bufr object in first argument. With no extra
## arguments, will copy (clone) everything. With 'metadata' as second
## argument, will copy just the metadata in section 0, 1 and 3 (and
## all of section 2 if present)
sub copy_from {
    my $self = shift;
    my $bufr = shift;
    _croak("First argument to copy_from must be a Geo::BUFR object")
        unless ref($bufr) eq 'Geo::BUFR';
    my $what = shift || 'all';
    if ($what eq 'metadata') {
        for (qw(
            BUFR_EDITION
            MASTER_TABLE CENTRE SUBCENTRE UPDATE_NUMBER OPTIONAL_SECTION
            DATA_CATEGORY INT_DATA_SUBCATEGORY LOC_DATA_SUBCATEGORY
            MASTER_TABLE_VERSION LOCAL_TABLE_VERSION YEAR MONTH DAY
            HOUR MINUTE SECOND LOCAL_USE DATA_SUBCATEGORY YEAR_OF_CENTURY
            NUM_SUBSETS OBSERVED_DATA COMPRESSED_DATA DESCRIPTORS_UNEXPANDED
            SEC2_STREAM
            )) {
            if (exists $bufr->{$_}) {
                $self->{$_} = $bufr->{$_};
            } else {
                # This cleanup might be necessary if BUFR edition changes
                delete $self->{$_} if exists $self->{$_};
            }
        }
    } elsif ($what eq 'all') {
        %$self = ();
        while (my ($key, $value) = each %{$bufr}) {
            if ($key eq 'FILEHANDLE') {
                # If a file has been associated with the copied
                # object, make a new filehandle rather than just
                # copying the reference
                $self->fopen($bufr->{FILENAME});
            } elsif (ref($value) and $key !~ /[BCD]_TABLE/) {
                # Copy the whole structure, not merely the reference.
                # Using Clone would be cheaper, but unfortunately
                # Clone is not a core module, while Storable is
                require Storable;
                import Storable qw(dclone);
                $self->{$key} = dclone($value);
            } else {
                $self->{$key} = $value;
            }
        }
    } else {
        _croak("Don't recognize second argument '$what' to copy_from()");
    }
    return 1;
}


##  Set debug level. Also set $Spew to true if debug level > 1 is set
##  (we don't bother to reset $Spew to 0 if all debug levels later are
##  reset to 0 or 1)
sub set_verbose {
    my $self = shift;
    my $verbose = shift;
    if (ref($self)) {
        # Just myself
        $self->{VERBOSE} = $verbose;
        $self->_spew(2, "Verbosity level for object set to %d", $verbose);
    } else {
        # Whole class
        $Verbose = $verbose;
        Geo::BUFR->_spew(2, "Verbosity level for class set to %d", $verbose);
    }
    $Spew = $verbose if $verbose > 1;
    return 1;
}

##  Turn off (or on) decoding of section 4
sub set_nodata {
    my $self = shift;
    my $n = shift;
    $Nodata = defined $n ? $n : 1; # Default is 1
    Geo::BUFR->_spew(2, "Nodata set to %d", $Nodata);
    return 1;
}

##  Turn off (or on) decoding of quality information
sub set_noqc {
    my $self = shift;
    my $n = shift;
    $Noqc = defined $n ? $n : 1; # Default is 1
    Geo::BUFR->_spew(2, "Noqc set to %d", $Noqc);
    return 1;
}

##  Require strict checking of BUFR format
sub set_strict_checking {
    my $self = shift;
    my $n = shift;
    _croak "Value for strict checking not provided"
        unless defined $n;
    $Strict_checking = $n;
    Geo::BUFR->_spew(2, "Strict_checking set to %d", $Strict_checking);
    return 1;
}

## Show replication descriptors (with X in FXY replaced by actual
## number of descriptors replicated, adjusted to 0 if > 99) and all
## data description operators when calling dumpsection4
sub set_show_all_operators {
    my $self = shift;
    my $n = shift;
    $Show_all_operators = defined $n ? $n : 1; # Default is 1
    $Show_replication = $Show_all_operators;
    Geo::BUFR->_spew(2, "Show_all_operators set to %d", $Show_all_operators);
    return 1;
}

## Accessor methods for BUFR sec0-3 ##
sub get_bufr_length {
    my $self = shift;
    return defined $self->{BUFR_LENGTH} ? $self->{BUFR_LENGTH} : undef;
}
sub set_bufr_edition {
    my ($self, $bufr_edition) = @_;
    _croak "BUFR edition number not provided in set_bufr_edition"
        unless defined $bufr_edition;
    _croak "BUFR edition number must be an integer, is '$bufr_edition'"
        unless $bufr_edition =~ /^\d+$/;
    _croak "Not an allowed value for BUFR edition number: $bufr_edition"
        unless $bufr_edition >= 0 and $bufr_edition < 5;
        # BUFR edition 0 is in fact in use in ECMWF MARS archive
    $self->{BUFR_EDITION} = $bufr_edition;
    return 1;
}
sub get_bufr_edition {
    my $self = shift;
    return defined $self->{BUFR_EDITION} ? $self->{BUFR_EDITION} : undef;
}
sub set_master_table {
    my ($self, $master_table) = @_;
    _croak "BUFR master table not provided in set_master_table"
        unless defined $master_table;
    _croak "BUFR master table must be an integer, is '$master_table'"
        unless $master_table =~ /^\d+$/;
    # Max value that can be stored in 1 byte is 255
    _croak "BUFR master table exceeds limit 255, is '$master_table'"
        if $master_table > 255;
    $self->{MASTER_TABLE} = $master_table;
    return 1;
}
sub get_master_table {
    my $self = shift;
    return defined $self->{MASTER_TABLE} ? $self->{MASTER_TABLE} : undef;
}
sub set_centre {
    my ($self, $centre) = @_;
    _croak "Originating/generating centre not provided in set_centre"
        unless defined $centre;
    _croak "Originating/generating centre must be an integer, is '$centre'"
        unless $centre =~ /^\d+$/;
    # Max value that can be stored in 2 bytes is 65535
    _croak "Originating/generating centre exceeds limit 65535, is '$centre'"
        if $centre > 65535;
    $self->{CENTRE} = $centre;
    return 1;
}
sub get_centre {
    my $self = shift;
    return defined $self->{CENTRE} ? $self->{CENTRE} : undef;
}
sub set_subcentre {
    my ($self, $subcentre) = @_;
    _croak "Originating/generating subcentre not provided in set_subcentre"
        unless defined $subcentre;
    _croak "Originating/generating subcentre must be an integer, is '$subcentre'"
        unless $subcentre =~ /^\d+$/;
    _croak "Originating/generating subcentre exceeds limit 65535, is '$subcentre'"
        if $subcentre > 65535;
    $self->{SUBCENTRE} = $subcentre;
    return 1;
}
sub get_subcentre {
    my $self = shift;
    return defined $self->{SUBCENTRE} ? $self->{SUBCENTRE} : undef;
}
sub set_update_sequence_number {
    my ($self, $update_number) = @_;
    _croak "Update sequence number not provided in set_update_sequence_number"
        unless defined $update_number;
    _croak "Update sequence number must be a nonnegative integer, is '$update_number'"
        unless $update_number =~ /^\d+$/;
    _croak "Update sequence number exceeds limit 255, is '$update_number'"
        if $update_number > 255;
    $self->{UPDATE_NUMBER} = $update_number;
    return 1;
}
sub get_update_sequence_number {
    my $self = shift;
    return defined $self->{UPDATE_NUMBER} ? $self->{UPDATE_NUMBER} : undef;
}
sub set_optional_section {
    my ($self, $optional_section) = @_;
    _croak "Optional section (0 or 1) not provided in set_optional_section"
        unless defined $optional_section;
    _croak "Optional section must be 0 or 1, is '$optional_section'"
        unless $optional_section eq '0' or $optional_section eq '1';
    $self->{OPTIONAL_SECTION} = $optional_section;
    return 1;
}
sub get_optional_section {
    my $self = shift;
    return defined $self->{OPTIONAL_SECTION} ? $self->{OPTIONAL_SECTION} : undef;
}
sub set_data_category {
    my ($self, $data_category) = @_;
    _croak "Data category not provided in set_data_category"
        unless defined $data_category;
    _croak "Data category must be an integer, is '$data_category'"
        unless $data_category =~ /^\d+$/;
    _croak "Data category exceeds limit 255, is '$data_category'"
        if $data_category > 255;
    $self->{DATA_CATEGORY} = $data_category;
    return 1;
}
sub get_data_category {
    my $self = shift;
    return defined $self->{DATA_CATEGORY} ? $self->{DATA_CATEGORY} : undef;
}
sub set_int_data_subcategory {
    my ($self, $int_data_subcategory) = @_;
    _croak "International data subcategory not provided in set_int_data_subcategory"
        unless defined $int_data_subcategory;
    _croak "International data subcategory must be an integer, is '$int_data_subcategory'"
        unless $int_data_subcategory =~ /^\d+$/;
    _croak "International data subcategory exceeds limit 255, is '$int_data_subcategory'"
        if $int_data_subcategory > 255;
    $self->{INT_DATA_SUBCATEGORY} = $int_data_subcategory;
    return 1;
}
sub get_int_data_subcategory {
    my $self = shift;
    return defined $self->{INT_DATA_SUBCATEGORY} ? $self->{INT_DATA_SUBCATEGORY} : undef;
}
sub set_loc_data_subcategory {
    my ($self, $loc_data_subcategory) = @_;
    _croak "Local subcategory not provided in set_loc_data_subcategory"
        unless defined $loc_data_subcategory;
    _croak "Local data subcategory must be an integer, is '$loc_data_subcategory'"
        unless $loc_data_subcategory =~ /^\d+$/;
    _croak "Local data subcategory exceeds limit 255, is '$loc_data_subcategory'"
        if $loc_data_subcategory > 255;
    $self->{LOC_DATA_SUBCATEGORY} = $loc_data_subcategory;
    return 1;
}
sub get_loc_data_subcategory {
    my $self = shift;
    return defined $self->{LOC_DATA_SUBCATEGORY} ? $self->{LOC_DATA_SUBCATEGORY} : undef;
}
sub set_data_subcategory {
    my ($self, $data_subcategory) = @_;
    _croak "Data subcategory not provided in set_data_subcategory"
        unless defined $data_subcategory;
    _croak "Data subcategory must be an integer, is '$data_subcategory'"
        unless $data_subcategory =~ /^\d+$/;
    _croak "Data subcategory exceeds limit 255, is '$data_subcategory'"
        if $data_subcategory > 255;
    $self->{DATA_SUBCATEGORY} = $data_subcategory;
    return 1;
}
sub get_data_subcategory {
    my $self = shift;
    return defined $self->{DATA_SUBCATEGORY} ? $self->{DATA_SUBCATEGORY} : undef;
}
sub set_master_table_version {
    my ($self, $master_table_version) = @_;
    _croak "Master table version not provided in set_master_table_version"
        unless defined $master_table_version;
    _croak "BUFR master table version must be an integer, is '$master_table_version'"
        unless $master_table_version =~ /^\d+$/;
    _croak "BUFR master table version exceeds limit 255, is '$master_table_version'"
        if $master_table_version > 255;
    $self->{MASTER_TABLE_VERSION} = $master_table_version;
    return 1;
}
sub get_master_table_version {
    my $self = shift;
    return defined $self->{MASTER_TABLE_VERSION}
        ? $self->{MASTER_TABLE_VERSION} : undef;
}
sub set_local_table_version {
    my ($self, $local_table_version) = @_;
    _croak "Local table version not provided in set_local_table_version"
        unless defined $local_table_version;
    _croak "Local table version must be an integer, is '$local_table_version'"
        unless $local_table_version =~ /^\d+$/;
    _croak "Local table version exceeds limit 255, is '$local_table_version'"
        if $local_table_version > 255;
    $self->{LOCAL_TABLE_VERSION} = $local_table_version;
    return 1;
}
sub get_local_table_version {
    my $self = shift;
    return defined $self->{LOCAL_TABLE_VERSION}
        ? $self->{LOCAL_TABLE_VERSION} : undef;
}
sub set_year_of_century {
    my ($self, $year_of_century) = @_;
    _croak "Year of century not provided in set_year_of_century"
        unless defined $year_of_century;
    _croak "Year of century must be an integer, is '$year_of_century'"
        unless $year_of_century =~ /^\d+$/;
    _complain "year_of_century > 100 in set_year_of_century: $year_of_century"
        if $year_of_century > 100;
    # A common mistake is to set year_of_century for year 2000 to 0, should be 100
    $self->{YEAR_OF_CENTURY} = $year_of_century == 0 ? 100 : $year_of_century;
    return 1;
}
sub get_year_of_century {
    my $self = shift;
    if (defined $self->{YEAR_OF_CENTURY}) {
        return $self->{YEAR_OF_CENTURY};
    } elsif (defined $self->{YEAR}) {
        my $yy = $self->{YEAR} % 100;
        return $yy == 0 ? 100 : $yy;
    } else {
        return undef;
    }
}
sub set_year {
    my ($self, $year) = @_;
    _croak "Year not provided in set_year"
        unless defined $year;
    _croak "Year must be an integer, is '$year'"
        unless $year =~ /^\d+$/;
    _croak "Year exceeds limit 65535, is '$year'"
        if $year > 65535;
    $self->{YEAR} = $year;
    return 1;
}
sub get_year {
    my $self = shift;
    return defined $self->{YEAR} ? $self->{YEAR} : undef;
}
sub set_month {
    my ($self, $month) = @_;
    _croak "Month not provided in set_month"
        unless defined $month;
    _croak "Month must be an integer, is '$month'"
        unless $month =~ /^\d+$/;
    _complain "Month must be 1-12 in set_month, is '$month'"
        if $month == 0 || $month > 12;
    $self->{MONTH} = $month;
    return 1;
}
sub get_month {
    my $self = shift;
    return defined $self->{MONTH} ? $self->{MONTH} : undef;
}
sub set_day {
    my ($self, $day) = @_;
    _croak "Day not provided in set_day"
        unless defined $day;
    _croak "Day must be an integer, is '$day'"
        unless $day =~ /^\d+$/;
    _complain "Day must be 1-31 in set_day, is '$day'"
        if $day == 0 || $day > 31;
    $self->{DAY} = $day;
    return 1;
}
sub get_day {
    my $self = shift;
    return defined $self->{DAY} ? $self->{DAY} : undef;
}
sub set_hour {
    my ($self, $hour) = @_;
    _croak "Hour not provided in set_hour"
        unless defined $hour;
    _croak "Hour must be an integer, is '$hour'"
        unless $hour =~ /^\d+$/;
    _complain "Hour must be 0-23 in set_hour, is '$hour'"
        if $hour > 23;
    $self->{HOUR} = $hour;
    return 1;
}
sub get_hour {
    my $self = shift;
    return defined $self->{HOUR} ? $self->{HOUR} : undef;
}
sub set_minute {
    my ($self, $minute) = @_;
    _croak "Minute not provided in set_minute"
        unless defined $minute;
    _croak "Minute must be an integer, is '$minute'"
        unless $minute =~ /^\d+$/;
    _complain "Minute must be 0-59 in set_minute, is '$minute'"
        if $minute > 59;
    $self->{MINUTE} = $minute;
    return 1;
}
sub get_minute {
    my $self = shift;
    return defined $self->{MINUTE} ? $self->{MINUTE} : undef;
}
sub set_second {
    my ($self, $second) = @_;
    _croak "Second not provided in set_second"
        unless defined $second;
    _croak "Second must be an integer, is '$second'"
        unless $second =~ /^\d+$/;
    _complain "Second must be 0-59 in set_second, is '$second'"
        if $second > 59;
    $self->{SECOND} = $second;
    return 1;
}
sub get_second {
    my $self = shift;
    return defined $self->{SECOND} ? $self->{SECOND} : undef;
}
sub set_local_use {
    my ($self, $local_use) = @_;
    _croak "Local use not provided in set_local use"
        unless defined $local_use;
    $self->{LOCAL_USE} = $local_use;
    return 1;
}
sub get_local_use {
    my $self = shift;
    return defined $self->{LOCAL_USE} ? $self->{LOCAL_USE} : undef;
}
sub set_number_of_subsets {
    my ($self, $number_of_subsets) = @_;
    _croak "Number of subsets not provided in set_number_of_subsets"
        unless defined $number_of_subsets;
    _croak "Number of subsets must be an integer, is '$number_of_subsets'"
        unless $number_of_subsets =~ /^\d+$/;
    _croak "Number of subsets exceeds limit 65535, is '$number_of_subsets'"
        if $number_of_subsets > 65535;
    $self->{NUM_SUBSETS} = $number_of_subsets;
    return 1;
}
sub get_number_of_subsets {
    my $self = shift;
    return defined $self->{NUM_SUBSETS} ? $self->{NUM_SUBSETS} : undef;
}
sub set_observed_data {
    my ($self, $observed_data) = @_;
    _croak "Observed data (0 or 1) not provided in set_observed_data"
        unless defined $observed_data;
    _croak "Observed data must be 0 or 1, is '$observed_data'"
        unless $observed_data eq '0' or $observed_data eq '1';
    $self->{OBSERVED_DATA} = $observed_data;
    return 1;
}
sub get_observed_data {
    my $self = shift;
    return defined $self->{OBSERVED_DATA} ? $self->{OBSERVED_DATA} : undef;
}
sub set_compressed_data {
    my ($self, $compressed_data) = @_;
    _croak "Compressed data (0 or 1) not provided in set_compressed_data"
        unless defined $compressed_data;
    _croak "Compressed data must be 0 or 1, is '$compressed_data'"
        unless $compressed_data eq '0' or $compressed_data eq '1';
    _complain "Not allowed to use compression for one subset messages!"
        if $compressed_data
            and defined $self->{NUM_SUBSETS} and $self->{NUM_SUBSETS} == 1;
    $self->{COMPRESSED_DATA} = $compressed_data;
    return 1;
}
sub get_compressed_data {
    my $self = shift;
    return defined $self->{COMPRESSED_DATA} ? $self->{COMPRESSED_DATA} : undef;
}
sub set_descriptors_unexpanded {
    my ($self, $descriptors_unexpanded) = @_;
    _croak "Unexpanded descriptors not provided in set_descriptors_unexpanded"
        unless defined $descriptors_unexpanded;
    $self->{DESCRIPTORS_UNEXPANDED} = $descriptors_unexpanded;
    return 1;
}
sub get_descriptors_unexpanded {
    my $self = shift;
    return defined $self->{DESCRIPTORS_UNEXPANDED}
        ? $self->{DESCRIPTORS_UNEXPANDED} : undef;
}
#############################################
## End of accessor methods for BUFR sec0-3 ##
#############################################

sub get_current_subset_number {
    my $self = shift;
    return defined $self->{CURRENT_SUBSET} ? $self->{CURRENT_SUBSET} : undef;
}

sub get_current_message_number {
    my $self = shift;
    return defined $self->{CURRENT_MESSAGE} ? $self->{CURRENT_MESSAGE} : undef;
}

sub get_current_ahl {
    my $self = shift;
    return defined $self->{CURRENT_AHL} ? $self->{CURRENT_AHL} : undef;
}

sub get_current_gts_starting_line {
    my $self = shift;
    return defined $self->{CURRENT_GTS_STARTING_LINE} ? $self->{CURRENT_GTS_STARTING_LINE} : undef;
}

sub get_current_gts_eom {
    my $self = shift;
    return defined $self->{CURRENT_GTS_EOM} ? $self->{CURRENT_GTS_EOM} : undef;
}

sub set_filter_cb {
    my $self = shift;
    my $cb   = shift;

    if (ref $cb eq 'CODE') {
        $self->{FILTER_CB} = $cb;
        @{$self->{FILTER_ARGS}} = ($self, @_);
    } else {
        $self->{FILTER_CB} = undef;
        delete $self->{FILTER_ARGS};
    }
    return 1;
}

sub is_filtered {
    my $self = shift;
    return defined $self->{IS_FILTERED} ? $self->{IS_FILTERED} : undef;
}

sub bad_bufrlength {
    my $self = shift;
    return defined $self->{BAD_LENGTH} ? $self->{BAD_LENGTH} : undef;
}

sub set_tableformat {
    my $self = shift;

    my $format = shift;
    _croak "Table format not provided. Possible values are BUFRDC and ECCODES"
        unless defined $format;
    _croak "Supported table formats are BUFRDC and ECCODES"
        unless uc($format) eq 'BUFRDC' || uc($format) eq 'ECCODES';
    $BUFR_table{FORMAT} = uc($format);
    Geo::BUFR->_spew(2, "BUFR table format set to %s", $BUFR_table{FORMAT});
    return 1;
}

sub get_tableformat {
    my $self = shift;
    return exists $BUFR_table{FORMAT} ? $BUFR_table{FORMAT} : '';
}

##  Set the path for BUFR table files
##  Usage: Geo::BUFR->set_tablepath(directory_list)
##         where directory_list is a list of colon-separated strings.
##  Example: Geo::BUFR->set_tablepath("/foo/bar:/foo/baz", "/some/where/else")
sub set_tablepath {
    my $self = shift;

    $BUFR_table{PATH} = join ":", map {split /:/} @_;
    Geo::BUFR->_spew(2, "BUFR table path set to %s", $BUFR_table{PATH});
    return 1;
}

sub get_tablepath {
    my $self = shift;

    if (exists $BUFR_table{PATH}) {
        return wantarray ? split(/:/, $BUFR_table{PATH}) : $BUFR_table{PATH};
    } else {
        return '';
    }
}

## Return table version from table if provided, or else from section 1
## information in BUFR message. For BUFRDC, this is a stripped down
## version of table name. For ECCODES, this is last path of table
## location (e.g. '0/wmo/29'), and a stringified list of two such
## paths (master and local) if local tables are used
## (e.g. '0/wmo/29,0/local/8/78/236'). Returns undef/empty list if
## impossible to determine table version.
sub get_table_version {
    my $self = shift;
    my $table = shift;

    if ($table) {
        if ($BUFR_table{FORMAT} eq 'BUFRDC') {
            # First check if this actually is an attempt to load an ECCODES table
            if ($table =~ /wmo/ || $table =~ /local/) {
                _croak("$table cannot be a BUFRDC table. "
                       . "Did you forget to set tableformat to ECCODES?");
            }
            (my $version = $table) =~ s/^(?:[BCD]?)(.*?)(?:\.TXT)?$/$1/;
            return $version;
        } elsif ($BUFR_table{FORMAT} eq 'ECCODES') {
            # Mainly meant to catch attempts to load a BUFRDC table
            # with tableformat mistakingly set to ECCODES
            _croak("$table cannot be an ecCodes table")
                unless ($table =~ /wmo/ || $table =~ /local/);
            return $table;
        }
    }

    # No table provided. Decide version from section 1 information.
    # First check that the necessary metadata exist
    foreach my $metadata (qw(MASTER_TABLE LOCAL_TABLE_VERSION
                             CENTRE SUBCENTRE)) {
        return undef if ! defined $self->{$metadata};
    }

    # If master table version, use centre 0 and subcentre 0 (in ECMWF
    # BUFRDC this is the convention from version 320 onwards)
    my $centre = $self->{CENTRE};
    my $subcentre = $self->{SUBCENTRE};
    my $local_table_version = $self->{LOCAL_TABLE_VERSION};
    if ($local_table_version == 0 || $local_table_version == 255) {
        $centre = 0;
        $subcentre = 0;
        $local_table_version = 0;
    }

    my $master_table = $self->{MASTER_TABLE};
    my $master_table_version = $self->{MASTER_TABLE_VERSION};
    if ($BUFR_table{FORMAT} eq 'BUFRDC') {
        # naming convention used in BUFRDC version >= 000270
        return sprintf "%03d%05d%05d%03d%03d",
               $master_table,$subcentre,$centre,$master_table_version,$local_table_version;
    } elsif ($BUFR_table{FORMAT} eq 'ECCODES')  {
        if ($local_table_version == 0) {
            return catfile($master_table,'wmo',$master_table_version);
        } else {
            return catfile($master_table,'wmo',$master_table_version) . ',' .
                   catfile($master_table,'local',$local_table_version,$centre,$subcentre);
        }
    }
}

# Return table version for the latest master table found in tablepath,
# in the same format as get_table_version. For use when master table
# version is not known, e.g. in bufrresolve.pl.
sub get_max_table_version {
    my ($self) = @_;

    _croak "BUFR table path not set, did you forget to call set_tablepath()?"
        unless $BUFR_table{PATH};

    my $max_version = 0;
    if ($BUFR_table{FORMAT} eq 'BUFRDC') {
        foreach my $tabledir (split /:/, $BUFR_table{PATH}) {
            opendir(my $dh, $tabledir) || _croak "Couldn't open $tabledir: $!";
            my @btables = sort grep { /^B0000000000000\d{3}000.TXT/ } readdir $dh;
            closedir $dh;
            my $version = substr($btables[-1], 14, 3)
                || _croak "Wrong tablepath or tableformat?";
            if ($version > $max_version) {
                $max_version = $version;
            }
        }

        _croak "No WMO master table found" unless $max_version;

        return '0000000000000' . $max_version . '000';

    } elsif ($BUFR_table{FORMAT} eq 'ECCODES') {
        foreach my $tabledir (split /:/, $BUFR_table{PATH}) {
            my $dir = catfile($tabledir,'0/wmo');
            opendir(my $dh, $dir) || _croak "Cannot open $dir: $!";
            my @files = sort {$a <=> $b} grep { /^[0-9]+$/ } readdir $dh;
            closedir $dh;

            my $version = $files[-1];
            if ($version > $max_version) {
                $max_version = $version;
            }
        }

        _croak "No WMO master table found" unless $max_version;

        return catfile('0', 'wmo', $max_version);
    }
}

# Search through $BUFR_table{PATH} to find first path for which $fname
# exists, or (for BUFRDC) if no such path exists, first path for which the
# corresponding master file exists, in which case
# $self->{LOCAL_TABLES_NOT_FOUND} is set to the local table initially
# searched for (this variable should be undefined as soon as the
# message is finished processing). Returns empty list if no such path
# could be found, else returns the path and the table name for which
# path was found.
sub _locate_table {
    my ($self,$fname) = @_;

    _croak "BUFR table path not set, did you forget to call set_tablepath()?"
        unless $BUFR_table{PATH};

    my $path;
    foreach (split /:/, $BUFR_table{PATH}) {
        if (-e catfile($_, $fname)) {
            $path = $_;
            $path =~ s|/$||;
            return ($path,$fname);
        }
    }

    if ($BUFR_table{FORMAT} eq 'BUFRDC') {
        # Path couldn't be found for $fname. Then try again for master table
        my $master_table;
        ($master_table,$path) = $self->_locate_master_table($fname);
        if ($path) {
            $self->{LOCAL_TABLES_NOT_FOUND} = $fname;
            return ($path,$master_table);
        }
    }

    # No table found
    return;
}

# Return master table and path corresponding to local table $fname, or
# empty list if $fname actually is a master table or if no path for the
# master table could be found.
sub _locate_master_table {
    my ($self,$fname) = @_;

    my $master_table;
    if ($BUFR_table{FORMAT} eq 'BUFRDC') {
        _croak("$fname is not a valid name for BUFRDC tables")
            if length($fname) < 20;
        $master_table = substr($fname,0,4) . '00000' . '00000'
            . substr($fname,14,3) . '000.TXT';
    } elsif ($BUFR_table{FORMAT} eq 'ECCODES')  {
        foreach my $metadata (qw(MASTER_TABLE MASTER_TABLE_VERSION)) {
            return if ! defined $self->{$metadata};
        }
        $master_table = catfile($self->{MASTER_TABLE},'wmo',$self->{MASTER_TABLE_VERSION});
    }
    return if ($master_table eq $fname); # Already tried

    my $path;
    foreach (split /:/, $BUFR_table{PATH}) {
        if (-e catfile($_, $master_table)) {
            $path = $_;
            $path =~ s|/$||;
            return ($master_table,$path);
        }
    }
    return;
}

## Read in a B table file into a hash, e.g.
##  $B_table{'001001'} = "WMO BLOCK NUMBER\0NUMERIC\0  0\0           0\0  7"
## where the B table values for 001001 are \0 (NUL) separated
sub _read_B_table_bufrdc {
    my ($self,$version) = @_;

    my $fname = "B$version.TXT";
    my ($path,$tname) = $self->_locate_table($fname)
        or _croak "Couldn't find BUFR table $fname in $BUFR_table{PATH}."
        . " Wrong tablepath?";

    # If we are forced to try master table because local table
    # couldn't be found, check if this might already have been loaded
    if ($tname ne $fname) {
        my $master_version = substr($tname,1,-4);
        return $BUFR_table{"B$master_version"} if exists $BUFR_table{"B$master_version"};
    }

    my $tablefile = catfile($path,$tname);
    open(my $TABLE, '<', $tablefile)
        or _croak "Couldn't open BUFR table B $tablefile: $!";
    my $txt = "Reading table $tablefile";
    $txt .= " (since local table " . $self->{LOCAL_TABLES_NOT_FOUND}
    . " couldn't be found)" if $self->{LOCAL_TABLES_NOT_FOUND};
    $self->_spew(1, "%s", $txt);

    my %B_table;
    while (<$TABLE>) {
        my ($s1,$fxy,$s2,$name,$s3,$unit,$s4,$scale,$s5,$refval,$s6,$bits)
            = unpack('AA6AA64AA24AA3AA12AA3', $_);
        next unless defined $bits;
        $name =~ s/\s+$//;
        $refval =~ s/-\s+(\d+)/-$1/; # Remove blanks between minus sign and value
        $B_table{$fxy} = join "\0", $name, $unit, $scale, $refval, $bits;
    }
    # When installing Geo::BUFR on Windows Vista with Strawberry Perl,
    # close sometimes returned an empty string. Therefore removed
    # check on return value for close.
    close $TABLE; # or _croak "Closing $tablefile failed: $!";

    $BUFR_table{"B$version"} = \%B_table;
    return \%B_table;
}

sub _read_B_table_eccodes {
    my ($self,$version) = @_;

    my ($path,$tname) = $self->_locate_table(catfile($version,'element.table'));

    if (! $path) {
        if ($version =~ /wmo/) {
            _croak "Couldn't find BUFR table " . catfile($version,'element.table')
                . " in $BUFR_table{PATH}. Wrong tablepath?";
        } else {
            # This might actually not be an error, since local table
            # might be provided for D only. But if later a local
            # element descriptor is requested, we should complain
            $self->{LOCAL_TABLES_NOT_FOUND} = $version;
            return;
        }
    }
    my $tablefile = catfile($path,$tname);

    open(my $TABLE, '<', $tablefile)
        or _croak "Couldn't open BUFR table B $tablefile: $!";
    $self->_spew(1, "Reading table %s", $tablefile);

    my %B_table;
    while (<$TABLE>) {
        # Skip comments (expexted to be in first line only)
        next if /^#/;

        # $rest is crex_unit|crex_scale|crex_width
        my ($code,$abbreviation,$type,$name,$unit,$scale,$reference,$width,$rest)
            = split /[|]/;
        next unless defined $width; # shouldn't happen
        $unit = 'CCITTIA5' if $unit eq 'CCITT IA5';
        $B_table{$code} = join "\0", $name, $unit, $scale, $reference, $width;
    }
    close $TABLE;

    $BUFR_table{"B$version"} = \%B_table;
    return \%B_table;
}

## Reads a D table file into a hash, e.g.
##  $D_table->{307080} = '301090 302031 ...'
## There are two different types of lines in D*.TXT, e.g.
##  307080 13 301090 BUFR template for synoptic reports
##            302031
## We choose to ignore the number of lines in expansion (here 13)
## because this number is sometimes in error. Instead we consider a
## line starting with 5 spaces to be of the second type above, else of
## the first type
sub _read_D_table_bufrdc {
    my ($self,$version) = @_;

    my $fname = "D$version.TXT";
    my ($path,$tname) = $self->_locate_table($fname)
        or _croak "Couldn't find BUFR table $fname in $BUFR_table{PATH}."
            . "Wrong tablepath?";

    # If we are forced to try master table because local table
    # couldn't be found, check if this might already have been loaded
    if ($tname ne $fname) {
        my $master_version = substr($tname,1,-4);
        return $BUFR_table{"D$master_version"} if exists $BUFR_table{"D$master_version"};
    }

    my $tablefile = catfile($path,$tname);
    open(my $TABLE, '<', $tablefile)
        or _croak "Couldn't open BUFR table D $tablefile: $!";
    my $txt = "Reading table $tablefile";
    $txt .= " (since local table " . $self->{LOCAL_TABLES_NOT_FOUND}
    . " couldn't be found)" if $self->{LOCAL_TABLES_NOT_FOUND};
    $self->_spew(1, "%s", $txt);

    my (%D_table, $alias);
    while (my $line = <$TABLE>) {
        $line =~ s/\s+$//;
        next if $line =~ /^\s*$/; # Blank line

        if (substr($line,0,5) eq ' ' x 5) {
            $line =~ s/^\s+//;
            $D_table{$alias} .= " $line";
        } else {
            $line =~ s/^\s+//;
            # In table version 17 a descriptor with more than 100
            # entries occurs, causing no space between alias and
            # number of entries (so split /\s+/ doesn't work)
            my ($ali, $skip, $desc) = unpack('A6A4A6', $line);
            $alias = $ali;
            $D_table{$alias} = $desc;
        }
    }
    close $TABLE; # or _croak "Closing $tablefile failed: $!";

    $BUFR_table{"D$version"} = \%D_table;
    return \%D_table;
}

sub _read_D_table_eccodes {
    my ($self,$version) = @_;

    my ($path,$tname) = $self->_locate_table(catfile($version,'sequence.def'));

    if (! $path) {
        if ($version =~ /wmo/) {
            _croak "Couldn't find BUFR table " . catfile($version,'sequence.def')
                . " in $BUFR_table{PATH}. Wrong tablepath?";
        } else {
            # This might actually not be an error, since local table
            # might be provided for B only. But if later a local
            # sequence descriptor is requested, we should complain
            $self->{LOCAL_TABLES_NOT_FOUND} = $version;
        }
        return;
    }
    my $tablefile = catfile($path,$tname);

    open(my $TABLE, '<', $tablefile)
        or _croak "Couldn't open BUFR table B $tablefile: $!";
    $self->_spew(1, "Reading table %s", $tablefile);

## sequence.def is expected to contain lines like
#"301196" = [  301011, 301013, 301021 ]
## which should be converted to
# 301196  3 301011
#           301013
#           301021
## Must also handle descriptors spanning more than one line, like
#"301046" = [  001007, 001012, 002048, 021119, 025060, 202124, 002026, 002027, 202000, 005040
#               ]
## and
#"301058" = [  301011, 301012, 201152, 202135, 004006, 202000, 201000, 301021, 020111, 020112,
#               020113, 020114, 020115, 020116, 020117, 020118, 020119, 025035, 020121, 020122,
#               020123, 020124, 025175, 020023, 025063, 202136, 201136, 002121, 201000, 202000,
#               025061, 002184, 002189, 025036, 101000, 031002, 301059 ]
    my %D_table;
    my $txt;
    while (<$TABLE>) {
        if (substr($_,0,1) eq '"') {
            # New sequence descriptor, parse and store the previous
            _parse_sequence(\%D_table,$txt) if $txt;
            chomp;
            $txt = $_;
        } else {
            chomp;
            $txt .= $_;
        }
    }
    _parse_sequence(\%D_table,$txt) if $txt;

    close $TABLE; # or _croak "Closing $tablefile failed: $!";

    $BUFR_table{"D$version"} = \%D_table;
    return \%D_table;
}

sub _parse_sequence {
    my ($Dtable, $txt) = @_;

    my ($seq, $rest) = ($txt =~ /^"(\d{6})" = \[(.*)\]/);
    my @list = split(/,/, $rest);
    foreach (@list) {
        s/^ +//;
        s/ +$//;
    }
    $Dtable->{$seq} = join(' ', @list);
}

## Read the flag and code tables, which in ECMWF BUFRDC tables are
## put in tables C$version.TXT (not to be confused with BUFR C tables,
## which contain the operator descriptors). Note that even though
## number of code values and number of lines are included in the
## tables, we choose to ignore them, because these values are often
## found to be in error. Instead we trust that the text starts at
## fixed positions in file. Returns reference to the C table, or undef
## if failing to open table file.
sub _read_C_table {
    my ($self,$version) = @_;

    # For ECCODES loading 2 different codetables directories might be necessary
    if ($BUFR_table{FORMAT} eq 'ECCODES') {
        if ($version =~ /,/) {
            my ($master, $local) = (split /,/, $version);
            $self->_read_C_table_eccodes($master);
            return $self->_read_C_table_eccodes($local);
        } else {
            return $self->_read_C_table_eccodes($version);
        }
    }

    # Rest of code is for BUFRDC
    my $fname = "C$version.TXT";
    my ($path,$tname) = $self->_locate_table($fname);
    return undef unless $path;

    # If we are forced to try master table because local table
    # couldn't be found, check if this might already have been loaded
    if ($tname ne $fname) {
        my $master_version = substr($tname,1,-4);
        return $BUFR_table{"C$master_version"} if exists $BUFR_table{"C$master_version"};
    }

    my $tablefile = catfile($path,$tname);
    open(my $TABLE, '<', $tablefile)
        or _croak "Couldn't open BUFR table C $tablefile: $!";
    my $txt = "Reading table $tablefile";
    $txt .= " (since local table " . $self->{LOCAL_TABLES_NOT_FOUND}
    . " couldn't be found)" if $self->{LOCAL_TABLES_NOT_FOUND};
    $self->_spew(1, "%s", $txt);

    my (%C_table, $table, $value);
    while (my $line = <$TABLE>) {
        $line =~ s/\s+$//;
        next if $line =~ /^\s*$/; # Blank line

        if (substr($line,0,15) eq ' ' x 15) {
            $line =~ s/^\s+//;
            next if $line eq 'NOT DEFINED' || $line eq 'RESERVED';
            $C_table{$table}{$value} .= $line . "\n";
        } elsif (substr($line,0,10) eq ' ' x 10) {
            $line =~ s/^\s+//;
            my ($val, $nlines, $txt) = split /\s+/, $line, 3;
            $value = $val+0;
            next if !defined $txt || $txt eq 'NOT DEFINED' || $txt eq 'RESERVED';
            $C_table{$table}{$value} .= $txt . "\n";
        } else {
            my ($tbl, $nval, $val, $nlines, $txt) = split /\s+/, $line, 5;
            $table = sprintf "%06d", $tbl;
            # For tables listed 2 or more times, use last instance only.
            # This prevents $txt to be duplicated in $C_table{$table}{$value}
            undef $C_table{$table} if defined $C_table{$table};
            $value = $val+0;
            next if !defined $txt || $txt eq 'NOT DEFINED' || $txt eq 'RESERVED';
            $C_table{$table}{$value} = $txt . "\n";
        }
    }
    close $TABLE; # or _croak "Closing $tablefile failed: $!";

    $BUFR_table{"C$version"} = \%C_table;
    return \%C_table;
}

sub _read_C_table_eccodes {
    my ($self,$version) = @_;

    my ($path,$tname) = $self->_locate_table(catfile($version,'codetables'));

    if (! $path) {
        if ($version =~ /wmo/) {
            _croak "Couldn't find BUFR table " . catfile($version,'element.table')
                . " in $BUFR_table{PATH}. Wrong tablepath?"
                if (! $path && $version =~ /wmo/);
        } else {
            # This might actually not be an error, if none of the
            # local descriptors are of type code or flag table. So
            # prefer to keep silent in this case.
            return;
        }
    }

    my $tabledir = catfile($path,$tname);

    opendir(my $dh, $tabledir) || _croak "Couldn't open $tabledir: $!";
    my @table_files = grep { /table$/ } readdir $dh;
    closedir($dh);
    $self->_spew(1, "Reading tables in %s", $tabledir) if @table_files;

    my %C_table;
    foreach my $table_file (@table_files) {
        my ($table) = ($table_file =~ /(\d+)\.table$/);
        die "Unexpected name of table file: $table_file" unless $table;
        $table =  sprintf "%06d", $table;

        open my $IN, '<', catfile($tabledir, $table_file)
            or _croak "Couldn't open $table_file: $!";
        while (<$IN>) {
            chomp;
            my ($num, $val, $txt) = split(/ /, $_, 3);
            _complain("Unexpected: first 2 fields in $table_file in $tabledir are unequal: $num $val")
                if ($Strict_checking and $num ne $val);

            # Fix a common problem in ecCodes codetables with long
            # lines, hopefully not changing valid use of '"' in local
            # tables (e.g. 8/78/0/codetables/8198.table:  ""Nebenamtliche"" measurement
            $txt =~ s/(?
##          $txt =~ s/" +//;

            $C_table{$table}{$val} = $txt . "\n";
        }

        _complain("$table_file in $tabledir is empty!")
            if ($Strict_checking and not $C_table{$table});
        close $IN;
    }

    $BUFR_table{"C$version"} = \%C_table;
    return \%C_table;
}

sub _get_tableid_eccodes {
    my $table_file = shift;
    my ($id) = ($table_file =~ /(\d+)\.table$/);
    return $id;
}


sub load_BDtables {
    my $self = shift;
    my $table = shift || '';

    my $version = $self->{TABLE_VERSION} = $self->get_table_version($table)
        or _croak "Not enough info to decide which tables to load";

    if ($BUFR_table{FORMAT} eq 'BUFRDC') {
        $self->{B_TABLE} = $BUFR_table{"B$version"} || $self->_read_B_table_bufrdc($version);
        $self->{D_TABLE} = $BUFR_table{"D$version"} || $self->_read_D_table_bufrdc($version);
    } elsif ($BUFR_table{FORMAT} eq 'ECCODES') {
        if ($version =~ /,/) {
            my ($master, $local) = (split /,/, $version);
            $self->{B_TABLE} = $BUFR_table{"B$master"} || $self->_read_B_table_eccodes($master);
            $self->{D_TABLE} = $BUFR_table{"D$master"} || $self->_read_D_table_eccodes($master);

            # Append local table to the master table (should work even if empty)
            my $local_Btable = (exists($BUFR_table{"B$local"})) ? $BUFR_table{"B$local"}
            : $self->_read_B_table_eccodes($local);
            @{$self->{B_TABLE}}{ keys %$local_Btable } = values %$local_Btable;
            my $local_Dtable = (exists($BUFR_table{"D$local"})) ? $BUFR_table{"D$local"}
            : $self->_read_D_table_eccodes($local);
            @{$self->{D_TABLE}}{ keys %$local_Dtable } = values %$local_Dtable;;

        } else {
            $self->{B_TABLE} = $BUFR_table{"B$version"} || $self->_read_B_table_eccodes($version);
            $self->{D_TABLE} = $BUFR_table{"D$version"} || $self->_read_D_table_eccodes($version);
        }
    }
    return $version;
}

sub load_Ctable {
    my $self = shift;
    my $table = shift || '';

    my $version = $self->get_table_version($table) || '';

    if ($version) {
        if ($BUFR_table{FORMAT} eq 'BUFRDC') {
            $self->{C_TABLE} = $BUFR_table{"C$version"} || $self->_read_C_table($version);
        } elsif ($BUFR_table{FORMAT} eq 'ECCODES') {
            if ($version =~ /,/) {
                my ($master, $local) = (split /,/, $version);
                $self->{C_TABLE} = $BUFR_table{"$master"} || $self->_read_C_table($master);

                # Append local table to the master table (should work even if empty)
                my $local_Ctable = (exists($BUFR_table{"C$local"})) ? $BUFR_table{"C$local"}
                : $self->_read_C_table_eccodes($local);
                @{$self->{C_TABLE}}{ keys %$local_Ctable } = values %$local_Ctable;

            } else {
                $self->{C_TABLE} = $BUFR_table{"C$version"} || $self->_read_C_table_eccodes($version);
            }
        }
    }

    if (not $self->{C_TABLE}) {
        # Was not able to load $table. Try latest master table instead.
        $version = $self->get_max_table_version()
            || _croak "No master tables found in tablepath";
        if ($BUFR_table{FORMAT} eq 'BUFRDC') {
            $self->{C_TABLE} = $BUFR_table{"C$version"} || $self->_read_C_table($version);
        } else {
            $self->{C_TABLE} = $BUFR_table{"C$version"} || $self->_read_C_table_eccodes($version);
        }
    }
    if (not $self->{C_TABLE}) {
        if ($BUFR_table{FORMAT} eq 'BUFRDC') {
            _croak "Unable to load C table (C$version.TXT)";
        } else {
            _croak "Unable to load codetables for $version";
        }
    }

    return $version;
}


##  Specify BUFR file to read
sub fopen {
    my $self = shift;
    my $filename = shift
        or _croak "fopen() called without an argument";
    _croak "File $filename doesn't exist!" unless -e $filename;
    _croak "$filename is not a plain file" unless -f $filename;

    # Open file for reading
    $self->{FILEHANDLE} = new FileHandle;
    open $self->{FILEHANDLE}, '<', $filename
        or _croak "Couldn't open file $filename for reading";

    $self->_spew(2, "File %s opened for reading", $filename);

    # For some OS this is necessary
    binmode $self->{FILEHANDLE};

    $self->{FILENAME} = $filename;
    return 1;
}

sub fclose {
    my $self = shift;
    if ($self->{FILEHANDLE}) {
        close $self->{FILEHANDLE}
            or _croak "Couldn't close BUFR file opened by fopen()";
        $self->_spew(2, "Closed file %s", $self->{FILENAME});
    }
    delete $self->{FILEHANDLE};
    delete $self->{FILENAME};
    # Much more might be considered deleted here, but usually the bufr
    # object goes out of scope immediately after a fclose anyway
    return 1;
}

sub eof {
    my $self = shift;
    return ($self->{EOF} || 0);
}

# Go to start of input buffer or start of file associated with the object
sub rewind {
    my $self = shift;
    if (exists $self->{FILEHANDLE}) {
        seek $self->{FILEHANDLE}, 0, 0 or _croak "Cannot seek: $!";
    } elsif (! $self->{IN_BUFFER}) {
        _croak "Cannot rewind: no file or input buffer associated with this object";
    }
    $self->{CURRENT_MESSAGE} = 0;
    $self->{CURRENT_SUBSET} = 0;
    delete $self->{START_POS};
    delete $self->{POS};
    delete $self->{EOF};
    return 1;
}

## Read in next BUFR message from file if $self->{FILEHANDLE} is set,
## else from $self->{IN_BUFFER} (string argument to
## constructor). Decodes section 0 and sets $self->{START_POS} to
## start of message and $self->{POS} to end of BUFR message (or after
## first 8 bytes of truncated/corrupt BUFR message for which we still
## want to attempt decoding). $self->{CURRENT_AHL} is updated if a GTS
## ahl is found (implemented for file reading only) and similarly for
## $self->{CURRENT_GTS_STARTING_LINE}, and $self->{EOF} is set if no
## more 'BUFR' in file/buffer. Croaks if an error occurs when reading
## BUFR message.

## Returns BUFR message from section 1 on, or undef if no BUFR message
## is found.
sub _read_message {
    my $self = shift;

    my $filehandle = $self->{FILEHANDLE} ? $self->{FILEHANDLE} : undef;
    my $in_buffer = $self->{IN_BUFFER} ? $self->{IN_BUFFER} : undef;
    _croak "_read_message: Neither BUFR file nor BUFR text is given"
        unless $filehandle or $in_buffer;

    # Locate next 'BUFR' and set $pos to this position in file/string,
    # also finding corresponding GTS ahl and starting line if exists
    # (for file only). Possibly sets $self->{EOF}
    my $pos = defined $self->{POS} ? $self->{POS} : 0;
    my ($ahl, $gts_start);
    ($pos, $ahl, $gts_start) = $self->_find_next_BUFR($filehandle, $in_buffer, $pos, '');
    return if $pos < 0;
    if ($ahl) {
        $self->{CURRENT_AHL} = $ahl;
        if ($gts_start) {
            $self->{CURRENT_GTS_STARTING_LINE} = $gts_start;
            $self->{GTS_CURRENT_EOM} = undef;
        }
    } else {
        $self->{CURRENT_AHL} = undef;
        $self->{CURRENT_GTS_STARTING_LINE} = undef;
    }

    # Remember start position of BUFR message in case we need to
    # rewind later because length of BUFR cannot be trusted
    $self->{START_POS} = $pos;

    # Report (if verbose setting) where we found the BUFR message
    $self->_spew(2, "BUFR message at position %d", $pos) if $Spew;

    # Read (rest) of Section 0 (length of BUFR message and edition number)
    my $sec0;                   # Section 0 is BUFR$sec0
    if ($filehandle) {
        if ((read $filehandle, $sec0, 8) != 8) {
            $self->{EOF} = 1;
            _croak "Error reading section 0 in file '$self->{FILENAME}', position "
                . tell($filehandle);
        }
        $sec0 = substr $sec0, 4;
    } else {
        if (length($in_buffer) < $pos+8) {
            $self->{EOF} = 1;
            _croak "Error reading section 0: this is not a BUFR message?"
        }
        $sec0 = substr $in_buffer, $pos+4, 4;
    }
    $self->{SEC0_STREAM}  = "BUFR$sec0";

    # Extract length and edition number
    my ($length, $edition) = unpack 'NC', "\0$sec0";
    $self->{BUFR_LENGTH}  = $length;
    $self->{BUFR_EDITION} = $edition;
    $self->_spew(2, "Message length: %d, Edition: %d", $length, $edition) if $Spew;
    _croak "Cannot handle BUFR edition $edition" if $edition < 2 || $edition > 4;

    # Read rest of BUFR message (section 1-5)
    my $msg;
    my $msgisOK = 1;
    if ($filehandle) {
        if ((read $filehandle, $msg, $length-8) != $length-8) {
            # Probably a corrupt or truncated BUFR message. We choose
            # to decode as much as possible (maybe the length in
            # section 0 is all that is wrong), but obviously we cannot
            # trust the stated length of BUFR message, so reset
            # position of filehandle to just after section 0
            $self->{BAD_LENGTH} = 1;
            $msgisOK = 0;
            seek $filehandle, $pos+8, 0;
            _complain("File %s not big enough to contain the stated"
                      . "length of BUFR message", $self->{FILENAME});
            $pos += 8;
        } else {
            $pos = tell($filehandle);
            if (substr($msg, -4) ne '7777') {
                $self->{BAD_LENGTH} = 1;
                _complain("BUFR length in sec 0 can't be correct, "
                          . "last 4 bytes are not '7777'");
            }
        }
    } else {
        if (length($in_buffer) < $pos+$length) {
            $self->{BAD_LENGTH} = 1;
            $msgisOK = 0;
            _complain("Buffer not big enough to contain the stated "
                      . "length of BUFR message");
            $msg = substr $in_buffer, $pos+8, $length-8;
            $pos += 8;
        } else {
            $msg = substr $in_buffer, $pos+8, $length-8;
            $pos += $length;
            if (substr($msg, -4) ne '7777') {
                $self->{BAD_LENGTH} = 1;
                _complain("BUFR length in sec 0 can't be correct, "
                          . "last 4 bytes are not '7777'");
            }
        }
    }
    if ($Spew) {
        if ($msgisOK) {
            $self->_spew(2, "Successfully read BUFR message; position now %d", $pos);
        } else {
            $self->_spew(2, "Resetting position to %d", $pos);
        }
    }

    # Reset $self->{POS} to end of BUFR message (or after first 8
    # bytes of truncated/corrupt BUFR message)
    $self->{POS} = $pos;

    # And then advance past GTS end of message if found
    my $gts_eom;
    if ($filehandle && ! $self->{BAD_LENGTH}) {
        if ((read $filehandle, $gts_eom, 4) == 4 && $gts_eom eq "\r\r\n\003") {
            $self->{CURRENT_GTS_EOM} = $gts_eom;
            $self->{POS} +=4;
        } else {
            # return to end of message position
            seek $filehandle, $pos, 0;
        }
    }

    return $msg;
}

# Note that our definition av AHL and GTS starting line differs
# slightly from that of the Manual on the GTS PART II. OPERATIONAL
# PROCEDURES FOR THE GLOBAL TELECOMMUNICATION SYSTEM (2.3.1 and 2.3.2)
# in that the Abbreviated heading in the Manual starts with \r\r\n
# which we have chosen to consider belonging to (the end of) the GTS
# starting line.

my $gts_start_regexp = qr{\001\r\r\n\d{3,5}\r\r\n};
# Allow both 3 and 5 digits channel sequence number

my $ahl_regex = qr{[A-Z]{4}\d\d [A-Z]{4} \d{6}(?: (?:(?:RR|CC|AA|PA)[A-Z])| COR| RTD)?};
# BBB=Pxx (segmentation) was allowed until 2007, but at least one
# centre still uses PAA as of 2014.  COR and RTD shouldn't be
# allowed (from ?), but are still used

## Advance to first occurrence of 'BUFR', or to the possibly preceding
## GTS envelope if this is requested in $at. Returns the new position
## and (if called in array context) the possibly preceding ahl and gts
## starting line. If no 'BUFR' is found, sets $self->{EOF} and returns
## -1 for the new position.
sub _find_next_BUFR {
    my $self = shift;
    my ($filehandle, $in_buffer, $pos, $at) = @_;

    my ($new_pos, $ahl, $gts_start);
    if ($filehandle) {
        my $oldeol = $/;
        $/ = "BUFR";
        my $slurp = <$filehandle> || '    ';
        $/ = $oldeol;
        if (CORE::eof($filehandle) or substr($slurp,-4) ne 'BUFR') {
            $self->{EOF} = 1;
        } else {
            # Get the GTS ahl (TTAAii CCCC DTG [BBB]) before 'BUFR',
            # if present. Use '\n+' not '\n' since adding an extra
            # '\n' in bulletin has been seen. Allow also for not
            # including \r\r (which might be how the bulletin file was
            # prepared originally, or might catch cases where ahl is
            # mistakingly included twice)
            my $reset = 4;
            if ($slurp =~ /(${gts_start_regexp}?)(${ahl_regex})((?:\r\r)?\n+BUFR)$/) {
                $gts_start = $1 || '';
                $ahl = $2;
                $reset = length($gts_start) + length($2) + length($3) if $at eq 'at_ahl';

                $self->_spew(2,"GTS ahl found: %s%s", $gts_start, $ahl) if $Spew;
            }
            # Reset position of filehandle to just before 'BUFR', or
            # if requested, before possible preceding AHL
            seek($filehandle, -$reset, 1);
            $new_pos = tell $filehandle;
        }
    } else {
        $new_pos = index($in_buffer, 'BUFR', $pos);
        if ($new_pos < 0) {
            $self->{EOF} = 1;
        } else {
            if (substr($in_buffer, $pos, $new_pos - $pos)
                =~ /(${gts_start_regexp}?)(${ahl_regex})((?:\r\r)?\n+)$/) {
                $gts_start = $1 || '';
                $ahl = $2;
                $self->_spew(2,"GTS ahl found: %s%s", $gts_start, $ahl) if $Spew;
                if ($at eq 'at_ahl') {
                    $new_pos -= length($gts_start) + length($2) + length($3);
                }
            }
        }
    }

    if ($self->{EOF}) {
        if ($pos == 0) {
            if ($filehandle) {
                $self->_spew(2,"No BUFR message in file %s", $self->{FILENAME})
                    if $Spew;
            } else {
                $self->_spew(2, "No BUFR message found") if $Spew;
            }
        }
        return -1;
    }

    return wantarray ? ($new_pos, $ahl, $gts_start) : $new_pos;
}

## Returns the BUFR message in raw (binary) form, '' if errors encountered
sub get_bufr_message {
    my $self = shift;

    if ($self->{BAD_LENGTH} || $self->{ERROR_IN_MESSAGE}) {
        $self->_spew(2, "Skipping erroneous BUFR message");
        return '';
    }
    if (!$self->{FILEHANDLE} && !$self->{IN_BUFFER}) {
        $self->_spew(2, "No file or input buffer associated with this object");
        return '';
    }
    if (!exists $self->{START_POS} || !$self->{BUFR_LENGTH}) {
        $self->_spew(2, "No bufr message to return");
        return '';
    }

    my $msg;
    if (exists $self->{FILEHANDLE}) {
        my $fh = $self->{FILEHANDLE};
        my $old_pos = tell($fh);
        seek($fh, $self->{START_POS}, 0);
        read($fh, $msg, $self->{BUFR_LENGTH});
        seek($fh, $old_pos, 0);
        $self->_spew(2, "BUFR message extracted from file");
    } elsif (exists $self->{IN_BUFFER}) {
        $msg = substr $self->{IN_BUFFER}, $self->{START_POS}, $self->{BUFR_LENGTH};
        $self->_spew(2, "BUFR message extracted");
    }

    return $msg;
}

## Decode section 1 to 5. Section 0 is already decoded in _read_message.
sub _decode_sections {
    my $self = shift;
    my $msg = shift;

    $self->{BUFR_STREAM}  = $msg;
    $self->{SEC1_STREAM}  = undef;
    $self->{SEC2_STREAM}  = undef;
    $self->{SEC3_STREAM}  = undef;
    $self->{SEC4_STREAM}  = undef;
    $self->{SEC5_STREAM}  = undef;

    # Breaking the rule that all debugging should be on lines starting
    # with 'BUFR.pm:', therefore using $verbose=6
    $self->_spew(6, "%s", $self->dumpsection0()) if $Spew;

    ##  Decode Section 1 (Identification Section)  ##

    $self->_spew(2, "Decoding section 1") if $Spew;

    # Extract Section 1 information
    if ($self->{BUFR_EDITION} < 4) {
        # N means 4 byte integer, so put an extra null byte ('\0') in
        # front of string to get first 3 bytes as integer
        my @sec1 =  unpack 'NC14', "\0" . $self->{BUFR_STREAM};

        # Check that stated length of section 1 makes sense
        _croak "Length of section 1 too small (< 17): $sec1[0]"
            if $sec1[0] < 17;
        _croak "Rest of BUFR message shorter (" . length($self->{BUFR_STREAM})
            . " bytes) than stated length of section 1 ($sec1[0] bytes)"
                if $sec1[0] > length($self->{BUFR_STREAM});

        push @sec1, (unpack 'a*', substr $self->{BUFR_STREAM},17,$sec1[0]-17);
        $self->{SEC1_STREAM} = substr $self->{BUFR_STREAM}, 0, $sec1[0];
        $self->{BUFR_STREAM} = substr $self->{BUFR_STREAM}, $sec1[0];
        $self->{SEC1}                 = \@sec1;
        $self->{MASTER_TABLE}         = $sec1[1];
        $self->{SUBCENTRE}            = $sec1[2];
        $self->{CENTRE}               = $sec1[3];
        $self->{UPDATE_NUMBER}        = $sec1[4];
        $self->{OPTIONAL_SECTION}     = vec($sec1[5] & 0x80,0,1); # 1. bit
        $self->{DATA_CATEGORY}        = $sec1[6];
        $self->{DATA_SUBCATEGORY}     = $sec1[7];
        $self->{MASTER_TABLE_VERSION} = $sec1[8];
        $self->{LOCAL_TABLE_VERSION}  = $sec1[9];
        $self->{YEAR_OF_CENTURY}      = $sec1[10];
        $self->{MONTH}                = $sec1[11];
        $self->{DAY}                  = $sec1[12];
        $self->{HOUR}                 = $sec1[13];
        $self->{MINUTE}               = $sec1[14];
        $self->{LOCAL_USE}            = $sec1[15];
        # In case previous message was edition 4
        foreach my $key (qw(INT_DATA_SUBCATEGORY LOC_DATA_SUBCATEGORY
                            YEAR SECOND)) {
            undef $self->{$key};
        }
    } elsif ($self->{BUFR_EDITION} == 4) {
        my @sec1 =  unpack 'NCnnC7nC5', "\0" . $self->{BUFR_STREAM};

        # Check that stated length of section 1 makes sense
        _croak "Length of section 1 too small (< 22): $sec1[0]"
            if $sec1[0] < 22;
        _croak "Rest of BUFR message shorter (" . length($self->{BUFR_STREAM})
            . " bytes) than stated length of section 1 ($sec1[0] bytes)"
                if $sec1[0] > length($self->{BUFR_STREAM});

        push @sec1, (unpack 'a*', substr $self->{BUFR_STREAM},22,$sec1[0]-22);
        $self->{SEC1_STREAM} = substr $self->{BUFR_STREAM}, 0, $sec1[0];
        $self->{BUFR_STREAM} = substr $self->{BUFR_STREAM}, $sec1[0];
        $self->{SEC1}                 = \@sec1;
        $self->{MASTER_TABLE}         = $sec1[1];
        $self->{CENTRE}               = $sec1[2];
        $self->{SUBCENTRE}            = $sec1[3];
        $self->{UPDATE_NUMBER}        = $sec1[4];
        $self->{OPTIONAL_SECTION}     = vec($sec1[5] & 0x80,0,1); # 1. bit
        $self->{DATA_CATEGORY}        = $sec1[6];
        $self->{INT_DATA_SUBCATEGORY} = $sec1[7];
        $self->{LOC_DATA_SUBCATEGORY} = $sec1[8];
        $self->{MASTER_TABLE_VERSION} = $sec1[9];
        $self->{LOCAL_TABLE_VERSION}  = $sec1[10];
        $self->{YEAR}                 = $sec1[11];
        $self->{MONTH}                = $sec1[12];
        $self->{DAY}                  = $sec1[13];
        $self->{HOUR}                 = $sec1[14];
        $self->{MINUTE}               = $sec1[15];
        $self->{SECOND}               = $sec1[16];
        $self->{LOCAL_USE} = ($sec1[0] > 22) ? $sec1[17] : undef;
        # In case previous message was edition 3 or lower
        foreach my $key (qw(DATA_SUBCATEGORY YEAR_OF_CENTURY)) {
            undef $self->{$key};
        }
    }
    $self->_spew(2, "BUFR edition: %d Optional section: %d Update sequence number: %d",
                $self->{BUFR_EDITION}, $self->{OPTIONAL_SECTION}, $self->{UPDATE_NUMBER}) if $Spew;
    $self->_spew(6, "%s", $self->dumpsection1()) if $Spew;

    $self->_validate_datetime() if ($Strict_checking);

    ##  Decode Section 2 (Optional Section) if present  ##

    $self->_spew(2, "Decoding section 2") if $Spew;

    if ($self->{OPTIONAL_SECTION}) {
        my @sec2 = unpack 'N', "\0" . $self->{BUFR_STREAM};

        # Check that stated length of section 2 makes sense
        _croak "Length of section 2 too small (< 4): $sec2[0]"
            if $sec2[0] < 4;
        _croak "Rest of BUFR message shorter (" . length($self->{BUFR_STREAM})
            . " bytes) than stated length of section 2 ($sec2[0] bytes)"
                if $sec2[0] > length($self->{BUFR_STREAM});

        push @sec2, substr $self->{BUFR_STREAM}, 4, $sec2[0]-4;
        $self->{SEC2_STREAM} = substr $self->{BUFR_STREAM}, 0, $sec2[0];
        $self->{BUFR_STREAM} = substr $self->{BUFR_STREAM}, $sec2[0];
        $self->{SEC2} = \@sec2;
        $self->_spew(2, "Length of section 2: %d", $sec2[0]) if $Spew;
    } else {
        $self->{SEC2} = undef;
        $self->{SEC2_STREAM} = undef;
    }

    ##  Decode Section 3 (Data Description Section)  ##

    $self->_spew(2, "Decoding section 3") if $Spew;

    my @sec3 = unpack 'NCnC', "\0".$self->{BUFR_STREAM};

    # Check that stated length of section 3 makes sense
    _croak "Length of section 3 too small (< 8): $sec3[0]"
        if $sec3[0] < 8;
    _croak "Rest of BUFR message shorter (" . length($self->{BUFR_STREAM})
        . " bytes) than stated length of section 3 ($sec3[0] bytes)"
            if $sec3[0] > length($self->{BUFR_STREAM});

    push @sec3, substr $self->{BUFR_STREAM},7,($sec3[0]-7)&0x0ffe; # $sec3[0]-7 will be reduced by one if odd integer,
                                                                   # so will not push last byte if length of sec3 is even,
                                                                   # which might happen for BUFR edition < 4 (padding byte)
    $self->{SEC3_STREAM} = substr $self->{BUFR_STREAM}, 0, $sec3[0];
    $self->{BUFR_STREAM} = substr $self->{BUFR_STREAM}, $sec3[0];

    $self->{SEC3}             = \@sec3;
    $self->{NUM_SUBSETS}      = $sec3[2];
    $self->{OBSERVED_DATA}    = vec($sec3[3] & 0x80,0,1); # extract 1. bit
    $self->{COMPRESSED_DATA}  = vec($sec3[3] & 0x40,1,1); # extract 2. bit
    $self->_spew(2, "Length of section 3: %d", $sec3[0]) if $Spew;
    $self->_spew(2, "Number of subsets: %d Observed data: %d Compressed data: %d",
                 $self->{NUM_SUBSETS}, $self->{OBSERVED_DATA}, $self->{COMPRESSED_DATA}) if $Spew;
    _complain("0 subsets in BUFR message")
        if ($Strict_checking and $self->{NUM_SUBSETS} == 0);
    _complain("Bits 3-8 in octet 7 in section 3 are not 0 (octet 7 = $sec3[3])")
        if ($Strict_checking and ($sec3[3] & 0x3f) != 0);
    if ($Spew == 6 || $Nodata) {
        my @unexpanded = _int2fxy(unpack 'n*', $self->{SEC3}[4]);
        $self->{DESCRIPTORS_UNEXPANDED} = @unexpanded ?
            join(' ', @unexpanded) : '';
        $self->_spew(6, "%s", $self->dumpsection3());
    }

    $self->{IS_FILTERED} = defined $self->{FILTER_CB}
        ? $self->{FILTER_CB}->(@{$self->{FILTER_ARGS}}) : 0;
    return if $self->{IS_FILTERED} || $Nodata;

    ##  Decode Section 4 (Data Section)  ##

    $self->_spew(2, "Decoding section 4") if $Spew;

    my $sec4_len = unpack 'N', "\0$self->{BUFR_STREAM}";
    $self->_spew(2, "Length of section 4: %d", $sec4_len) if $Spew;

    # Check that stated length of section 4 makes sense
    _croak "Length of section 4 too small (< 4): $sec4_len"
        if $sec4_len < 4;
    _croak "Rest of BUFR message (" . length($self->{BUFR_STREAM}) . " bytes)"
        . " shorter than stated length of section 4 ($sec4_len bytes)."
        . " Probably the BUFR message is truncated"
        if $sec4_len > length($self->{BUFR_STREAM});

    $self->{SEC4_STREAM}  = substr $self->{BUFR_STREAM}, 0, $sec4_len;
    $self->{SEC4_RAWDATA} = substr $self->{BUFR_STREAM}, 4, $sec4_len-4;
    $self->{BUFR_STREAM}  = substr $self->{BUFR_STREAM}, $sec4_len;

    ##  Decode Section 5 (End Section)  ##

    $self->_spew(2, "Decoding section 5") if $Spew;

    # Next 4 characters should be '7777' and these should be end of
    # message, but allow more characters (i.e. length of message in
    # section 0 has been set too big) if $Strict_checking not set
    my $str = $self->{BUFR_STREAM};
    my $len = length($str);
    if ($len > 4
        || ($len == 4 && substr($str,0,4) ne '7777')) {
        my $err_msg = "Section 5 is not '7777' but the $len"
            . " characters (in hex): "
                . join(' ', map {sprintf "0x%02X", $_} unpack('C*', $str));
        if ($len > 4 && substr($str,0,4) eq '7777') {
            _complain($err_msg);
        } elsif ($len == 4 && substr($str,0,4) ne '7777') {
            _croak($err_msg);
        }
    }

    return;
}

##  Read next BUFR message and decode. Set $self->{ERROR_IN_MESSAGE} if
##  anything goes seriously wrong, so that sub next_observation can use
##  this to skip to next message if user chooses to trap the call to
##  next_observation in an eval and then calls next_observation again.
sub _next_message {
    my $self = shift;

    $self->_spew(2, "Reading next BUFR message") if $Spew;

    $self->{ERROR_IN_MESSAGE} = 0;
    $self->{BAD_LENGTH} = 0;

    my $msg;
    eval {
        # Read BUFR message and decode section 0 (needed to get length
        # of message)
        $msg = $self->_read_message();

        # Unpack section 1-5
        $self->_decode_sections($msg) if $msg;
    };
    if ($@) {
        $self->{ERROR_IN_MESSAGE} = 1;
        $self->{CURRENT_MESSAGE}++;
        die $@;  # Could use croak, but then 2 "at ... line ..."  will
                 # be printed to STDERR
    }
    if (!$msg) {
        # Nothing to decode. $self->{EOF} should have been set
        $self->_spew(2, "No more BUFR messages found") if $Spew;
        return;
    }

    $self->{CURRENT_MESSAGE}++;

    return if $Nodata || $self->{IS_FILTERED};

    # Load the relevant code tables
    my $table_version;
    eval { $table_version = $self->load_BDtables() };
    if ($@) {
        $self->{ERROR_IN_MESSAGE} = 1;
        die $@;
    }

    # Get the data descriptors and expand them
    my @unexpanded = _int2fxy(unpack 'n*', $self->{SEC3}[4]);
    _croak "No data description in section 3" if !defined $unexpanded[0];
    # Using master table because local tables couldn't be found is
    # risky, so catch missing descriptors here to be able to give
    # informative error messages
    $self->_check_descriptors(\@unexpanded) if $self->{LOCAL_TABLES_NOT_FOUND};
    $self->{DESCRIPTORS_UNEXPANDED} = join ' ', @unexpanded;
    $self->_spew(2, "Unexpanded data descriptors: %s", $self->{DESCRIPTORS_UNEXPANDED}) if $Spew;

    $self->_spew(2, "Expanding data descriptors") if $Spew;
    my $alias = "$table_version " . $self->{DESCRIPTORS_UNEXPANDED};
    if (exists $Descriptors_already_expanded{$alias}) {
        $self->{DESCRIPTORS_EXPANDED} = $Descriptors_already_expanded{$alias};
    } else {
        eval {
            $Descriptors_already_expanded{$alias} = $self->{DESCRIPTORS_EXPANDED}
                = join " ", _expand_descriptors($self->{D_TABLE}, @unexpanded);
        };
        if ($@) {
            $self->{ERROR_IN_MESSAGE} = 1;
            die $@;
        }
    }

    # Unpack data from bitstream
    $self->_spew(2, "Unpacking data") if $Spew;
    eval {
        if ($self->{COMPRESSED_DATA}) {
            $self->_decompress_bitstream();
        } else {
            $self->_decode_bitstream();
        }
    };
    if ($@) {
        $self->{ERROR_IN_MESSAGE} = 1;
        die $@;
    }

    return;
}

## Check if all element and sequence descriptors given are found in
## B/D-tables (but skip check for those preceded by 206-operator)
sub _check_descriptors {
    my ($self,$unexpanded) = @_;

    my $B_table = $self->{B_TABLE};
    my $D_table = $self->{D_TABLE};
    my $skip_next = 0;
    foreach my $id (@{$unexpanded}) {
        # Skip descriptors preceded by 206-operator
        if ($skip_next) {
            $skip_next = 0;
        } elsif (substr($id,0,3) eq '206') {
            $skip_next = 1;
        } elsif ( (substr($id,0,1) eq '0' && ! exists $B_table->{$id})
            || (substr($id,0,1) eq '3' && ! exists $D_table->{$id}) ) {
            my $version = ($BUFR_table{FORMAT} eq 'BUFRDC')
                ? substr($self->{LOCAL_TABLES_NOT_FOUND},1,-4)
                : $self->{LOCAL_TABLES_NOT_FOUND};
            undef $BUFR_table{"B$version"};
            undef $BUFR_table{"D$version"};
            $self->{ERROR_IN_MESSAGE} = 1;
            _croak("Data descriptor $id is not in master table."
                . " You need to get the local tables B/D$version.TXT");
        }
    }
    return;
}

##  Get next observation, i.e. next subset in current BUFR message or
##  first subset in next message. Returns (reference to) data and
##  descriptors, or empty list if either no observation is found (in
##  which case $self->{EOF} should have been set) or if decoding of
##  section 4 is not requested (in which case all of sections 0-3 have
##  been decoded in next message).
sub next_observation {
    my $self = shift;

    $self->_spew(2, "Fetching next observation") if $Spew;

    # If an error occurred during decoding of previous message, we
    # don't know if stated length in section 0 is to be trusted,
    # so rewind to next 'BUFR', or setting EOF if no such exists
    if ($self->{ERROR_IN_MESSAGE}) {
        # First rewind to right after 'BUFR' in previous (faulty)
        # message. We cannot go further if file/buffer starts as
        # 'BUFRBUFR'
        my $pos = $self->{START_POS} + 4;
        seek($self->{FILEHANDLE}, $pos, 0) if $self->{FILEHANDLE};
        $self->_spew(2, "Error in processing BUFR message (check STDERR for "
                     . "details), rewinding to next 'BUFR'") if $Spew;
        # Prepare for (a possible) next call to _read_message by
        # advancing to next 'BUFR', not skipping a preceding ahl
        my $new_pos = $self->_find_next_BUFR($self->{FILEHANDLE},
                                                    $self->{IN_BUFFER},$pos,'at_ahl');
        if ($self->{EOF}) {
            $self->_spew(2, "Last BUFR message (reached end of file)") if $Spew;
            return;
        } else {
            $self->{POS} = $new_pos;
        }
    }

    # Read next BUFR message
    if ($self->{CURRENT_MESSAGE} == 0
        or $self->{ERROR_IN_MESSAGE}
        or $self->{CURRENT_SUBSET} >= $self->{NUM_SUBSETS}) {

        $self->{CURRENT_SUBSET} = 0;
        # The bit maps must be rebuilt for each message
        undef $self->{BITMAPS};
        undef $self->{BITMAP_OPERATORS};
        undef $self->{BITMAP_START};
        undef $self->{REUSE_BITMAP};
        $self->{NUM_BITMAPS} = 0;
        $self->{BACKWARD_DATA_REFERENCE} = 1;
        # Some more tidying after decoding of previous message might
        # be necessary
        $self->{NUM_CHANGE_OPERATORS} = 0;
        undef $self->{CHANGE_WIDTH};
        undef $self->{CHANGE_CCITTIA5_WIDTH};
        undef $self->{CHANGE_SCALE};
        undef $self->{CHANGE_REFERENCE_VALUE};
        undef $self->{NEW_REFVAL_OF};
        undef $self->{CHANGE_SRW};
        undef $self->{ADD_ASSOCIATED_FIELD};
        undef $self->{LOCAL_TABLES_NOT_FOUND};
        undef $self->{DATA};
        undef $self->{DESC};
        # Note that we should NOT undef metadata in section 1-3 here,
        # since if the next call (_next_message) finds no more
        # messages, we don't want to lose the metadata of the last
        # valid message extracted. sub join_subsets is based on this
        # assumption

        $self->_next_message();
        return if $self->{EOF};

        if ($Nodata || $self->{IS_FILTERED}) {
            # Make a simple check that section 4 and 5 are complete
            if ($self->{BAD_LENGTH}) {
                # We could have set $self->{ERROR_IN_MESSAGE} here and
                # let next_observation() take care of the rewinding.
                # But we don't want error messages to be displayed if
                # e.g. message is to be filtered
                $self->{POS} = $self->{START_POS} + 4;
                seek($self->{FILEHANDLE}, $self->{POS}, 0) if $self->{FILEHANDLE};
                $self->_spew(2, "Possibly truncated message found (last 4 bytes"
                             . " are not '7777'), so rewinding to position %d",
                             $self->{POS}) if $Spew;
            }
            # This will ensure next call to next_observation to read next message
            $self->{CURRENT_SUBSET} = $self->{NUM_SUBSETS};
            return;
        }
    }

    $self->{CURRENT_SUBSET}++;

    # Return references to data and descriptor arrays
    if ($self->{COMPRESSED_DATA}) {
        return ($self->{DATA}[$self->{CURRENT_SUBSET}],
                $self->{DESC});
    } else {
        return ($self->{DATA}[$self->{CURRENT_SUBSET}],
                $self->{DESC}[$self->{CURRENT_SUBSET}]);
    }
}

# Dumping contents of a subset (including section 0, 1 and 3 if this is
# first subset) in a BUFR message, also displaying message number and
# ahl (if found) and subset number
sub dumpsections {
    my $self = shift;
    my $data = shift;
    my $descriptors = shift;
    my $options = shift || {};

    my $width = $options->{width} || 15;
    my $bitmap = exists $options->{bitmap} ? $options->{bitmap} : 1;

    my $current_subset_number = $self->get_current_subset_number();
    my $current_message_number = $self->get_current_message_number();
    my $current_ahl = $self->get_current_ahl() || '';

    my $txt;
    if ($current_subset_number == 1) {
        $txt = "\nMessage $current_message_number";
        $txt .= defined $current_ahl ? "  $current_ahl\n" : "\n";
        $txt .= $self->dumpsection0() . $self->dumpsection1() . $self->dumpsection3();
    }

    # If this is last message and there is a BUFR formatting error
    # caught by user with eval, we might end up here with current
    # subset number 0 (and no section 4 to dump)
    if ($current_subset_number > 0) {
        $txt .= "\nSubset $current_subset_number\n";
        $txt .= $bitmap ? $self->dumpsection4_with_bitmaps($data,$descriptors,
                                 $current_subset_number,$width)
                        : $self->dumpsection4($data,$descriptors,$width);
    }

    return $txt;
}

sub dumpsection0 {
    my $self = shift;
    _croak "BUFR object not properly initialized to call dumpsection0. "
        . "Did you forget to call next_observation()?" unless $self->{BUFR_LENGTH};

    my $txt = <<"EOT";

Section 0:
    Length of BUFR message:            $self->{BUFR_LENGTH}
    BUFR edition:                      $self->{BUFR_EDITION}
EOT
    return $txt;
}

sub dumpsection1 {
    my $self = shift;
    _croak "BUFR object not properly initialized to call dumpsection1. "
        . "Did you forget to call next_observation()?" unless $self->{SEC1_STREAM};

    my $txt;
    if ($self->{BUFR_EDITION} < 4) {
        $txt = <<"EOT";

Section 1:
    Length of section:                 @{[ length $self->{SEC1_STREAM} ]}
    BUFR master table:                 $self->{MASTER_TABLE}
    Originating subcentre:             $self->{SUBCENTRE}
    Originating centre:                $self->{CENTRE}
    Update sequence number:            $self->{UPDATE_NUMBER}
    Optional section present:          $self->{OPTIONAL_SECTION}
    Data category (table A):           $self->{DATA_CATEGORY}
    Data subcategory:                  $self->{DATA_SUBCATEGORY}
    Master table version number:       $self->{MASTER_TABLE_VERSION}
    Local table version number:        $self->{LOCAL_TABLE_VERSION}
    Year of century:                   $self->{YEAR_OF_CENTURY}
    Month:                             $self->{MONTH}
    Day:                               $self->{DAY}
    Hour:                              $self->{HOUR}
    Minute:                            $self->{MINUTE}
EOT
    } else {
        $txt = <<"EOT";

Section 1:
    Length of section:                 @{[ length $self->{SEC1_STREAM} ]}
    BUFR master table:                 $self->{MASTER_TABLE}
    Originating centre:                $self->{CENTRE}
    Originating subcentre:             $self->{SUBCENTRE}
    Update sequence number:            $self->{UPDATE_NUMBER}
    Optional section present:          $self->{OPTIONAL_SECTION}
    Data category (table A):           $self->{DATA_CATEGORY}
    International data subcategory:    $self->{INT_DATA_SUBCATEGORY}
    Local data subcategory:            $self->{LOC_DATA_SUBCATEGORY}
    Master table version number:       $self->{MASTER_TABLE_VERSION}
    Local table version number:        $self->{LOCAL_TABLE_VERSION}
    Year:                              $self->{YEAR}
    Month:                             $self->{MONTH}
    Day:                               $self->{DAY}
    Hour:                              $self->{HOUR}
    Minute:                            $self->{MINUTE}
    Second:                            $self->{SECOND}
EOT
    }
    # Last part of section 1: "Reserved for local use by ADP centres"
    # is considered so uninteresting (and rare), that it is displayed
    # only if verbose >= 2, in a _spew statement. Note that for BUFR
    # edition < 4 there is always one byte here (to make an even
    # number of bytes in section 1).
    $self->_spew(2, "Reserved for local use:             0x@{[unpack('H*', $self->{LOCAL_USE})]}")
        if $self->{LOCAL_USE} and length $self->{LOCAL_USE} > 1;

    return $txt;
}

sub dumpsection2 {
    my $self = shift;
    return '' if not defined $self->{SEC2};

    my $sec2_code_ref = shift;
    _croak "dumpsection2: no code ref provided"
        unless defined $sec2_code_ref && ref($sec2_code_ref) eq 'CODE';

    my $txt = <<"EOT";

Section 2:
    Length of section:                 @{[ length $self->{SEC2_STREAM} ]}
EOT

    return $txt . $sec2_code_ref->($self->{SEC2_STREAM}) . "\n";
}

sub dumpsection3 {
    my $self = shift;
    _croak "BUFR object not properly initialized to call dumpsection3. "
        . "Did you forget to call next_observation()?" unless $self->{SEC3_STREAM};
    $self->{DESCRIPTORS_UNEXPANDED} ||= '';

    my $txt = <<"EOT";

Section 3:
    Length of section:                 @{[ length $self->{SEC3_STREAM} ]}
    Number of data subsets:            $self->{NUM_SUBSETS}
    Observed data:                     $self->{OBSERVED_DATA}
    Compressed data:                   $self->{COMPRESSED_DATA}
    Data descriptors unexpanded:       $self->{DESCRIPTORS_UNEXPANDED}
EOT
    return $txt;
}

sub dumpsection4 {
    my $self = shift;
    my $data = shift;
    my $descriptors = shift;
    my $width = shift || 15;    # Optional argument
    # Since last (optional) argument to dumpsection() is an anonymous
    # hash, check that this is not mistakenly applied here also
    _croak "Last optional argument to dumpsection4 should be integer"
        if ref($width) || $width !~ /^\d+$/;

    my $txt = "\n";
    my $B_table = $self->{B_TABLE};
    # Add the artificial descriptor for associated field
    $B_table->{999999} = "ASSOCIATED FIELD\0NUMERIC";
    my $C_table = $self->{C_TABLE} || '';
    my $idx = 0;
    my $line_no = 0;    # Precede each line with a line number, except
                        # for replication descriptors and for operator
                        # descriptors with no data value in section 4
  ID:
    foreach my $id (@{$descriptors}) {
        my $value = defined $data->[$idx] ? $data->[$idx] : 'missing';
        $idx++;
        my $f = substr($id, 0, 1);
        if ($f == 1) {
            $txt .= sprintf "        %6d\n", $id;
            next ID;
        } elsif ($f == 2) {
            if ($id =~ /^205/) {    # Character information operator
                $txt .= sprintf "%6d  %06d  %${width}.${width}s  %s\n",
                    ++$line_no, $id, $value, "CHARACTER INFORMATION";
                next ID;
            } else {
                my $operator_name = _get_operator_name($id);
                if ($operator_name) {
                    $txt .= sprintf "        %06d  %${width}.${width}s  %s\n",
                        $id, "", $operator_name;
                }
                next ID;
            }
        } elsif ($f == 9 && $id != 999999) {
            $txt .= sprintf "%6d  %06d  %${width}.${width}s  %s %06d\n",
                ++$line_no, $id, $value, 'NEW REFERENCE VALUE FOR', $id - 900000;
            next ID;
        } elsif ($id == 31031) { # This is the only data descriptor
                                 # where all bits set to one should
                                 # not be rendered as missing value
                                 # (for replication/repetition factors in
                                 # class 31 $value has been adjusted already)
            $value = 1 if $value eq 'missing';
        }
        _croak "Data descriptor $id is not present in BUFR table B"
            unless exists $B_table->{$id};
        my ($name, $unit, $bits) = (split /\0/, $B_table->{$id})[0,1,4];
        # Code or flag table number equals $id, so no need to display this in [unit]
        my $short_unit = $unit;
        my $unit_start = uc(substr($unit, 0, 4));
        if ($unit_start eq 'CODE') {
            $short_unit = 'CODE TABLE';
        } elsif ($unit_start eq 'FLAG') {
            $short_unit = 'FLAG TABLE';
        }
        $txt .= sprintf "%6d  %06d  %${width}.${width}s  %s\n",
            ++$line_no, $id, $value, "$name [$short_unit]";

        # Check for illegal flag value
        if ($Strict_checking && $short_unit eq 'FLAG TABLE' && $bits > 1) {
            if ($value ne 'missing' && $value % 2) {
                $bits += 0; # get rid of spaces
                my $max_value = 2**$bits - 1;
                _complain("$id - $value: rightmost bit $bits is set indicating missing value"
                          . " but then value should be $max_value");
            }
        }

        # Resolve flag and code table values if code table is loaded
        # (but don't bother about 031031 - too much uninformative output)
        if ($C_table && $id != 31031 && $value ne 'missing') {
            my $num_spaces = $width + 18;
            $txt .= _get_code_table_txt($id,$value,$unit,$B_table,$C_table,$num_spaces)
        }
    }
    return $txt;
}

# Operators which should always be displayed in dumpsection4
my %OPERATOR_NAME_A =
    ( 222000 => 'QUALITY INFORMATION FOLLOW',
      223000 => 'SUBSTITUTED VALUES FOLLOW',
      224000 => 'FIRST ORDER STATISTICS FOLLOW',
      225000 => 'DIFFERENCE STATISTICAL VALUES FOLLOW',
      232000 => 'REPLACE/RETAINED VALUES FOLLOW',
      235000 => 'CANCEL BACKWARD DATA REFERENCE',
      236000 => 'DEFINE DATA PRESENT BIT MAP',
      237000 => 'USE PREVIOUSLY DEFINED BIT MAP',
 );
# Operators which should normally not be displayed in dumpsection4
my %OPERATOR_NAME_B =
    ( 201000 => 'CANCEL CHANGE DATA WIDTH',
      202000 => 'CANCEL CHANGE SCALE',
      203000 => 'CANCEL CHANGE REFERENCE VALUES',
      207000 => 'CANCEL INCREASE SCALE, REFERENCE VALUE AND DATA WIDTH',
      208000 => 'CANCEL CHANGE WIDTH OF CCITT IA5 FIELD',
      203255 => 'STOP CHANGING REFERENCE VALUES',
      223255 => 'SUBSTITUTED VALUES MARKER OPERATOR',
      224255 => 'FIRST ORDER STATISTICAL VALUES MARKER OPERATOR',
      225255 => 'DIFFERENCE STATISTICAL STATISTICAL VALUES MARKER OPERATOR',
      232255 => 'REPLACED/RETAINED VALUES MARKER OPERATOR',
      237255 => 'CANCEL DEFINED DATA PRESENT BIT MAP',
 );
# Operator classes which should normally not be displayed in dumpsection4
my %OPERATOR_NAME_C =
    ( 201 => 'CHANGE DATA WIDTH',
      202 => 'CHANGE SCALE',
      203 => 'CHANGE REFERENCE VALUES',
      204 => 'ADD ASSOCIATED FIELD',
      # This one is displayed, treated specially (and named CHARACTER INFORMATION)
##      205 => 'SIGNIFY CHARACTER',
      206 => 'SIGNIFY DATA WIDTH FOR THE IMMEDIATELY FOLLOWING LOCAL DESCRIPTOR',
      207 => 'INCREASE SCALE, REFERENCE VALUE AND DATA WIDTH',
      208 => 'CHANGE WIDTH OF CCITT IA5 FIELD',
      221 => 'DATA NOT PRESENT',
 );
sub _get_operator_name {
    my $id = shift;
    my $operator_name = '';
    if ($OPERATOR_NAME_A{$id}) {
        $operator_name = $OPERATOR_NAME_A{$id}
    } elsif ($Show_all_operators) {
        if ($OPERATOR_NAME_B{$id}) {
            $operator_name = $OPERATOR_NAME_B{$id}
        } else {
            my $fx = substr $id, 0, 3;
            if ($OPERATOR_NAME_C{$fx}) {
                $operator_name = $OPERATOR_NAME_C{$fx};
            }
        }
    }
    return $operator_name;
}

## Display bit mapped values on same line as the original value. This
## offer a much shorter and easier to read dump of section 4 when bit
## maps has been used (i.e. for 222000 quality information, 223000
## substituted values, 224000 first order statistics, 225000
## difference statistics, 232000 replaced/retained values). '*******'
## is displayed if data is not present in bit map (bit set to 1 in
## 031031 or data not covered by the 031031 descriptors), 'missing' is
## displayed if value is missing.  But note that we miss other
## descriptors like 001031 and 001032 if these come after 222000 etc
## with the current implementation. And there are more shortcomings,
## described in CAVEAT section in POD for bufrread.pl
sub dumpsection4_with_bitmaps {
    my $self = shift;
    my $data = shift;
    my $descriptors = shift;
    my $isub = shift;
    my $width = shift || 15;    # Optional argument

    # If no bit maps call the ordinary dumpsection4
    if (not defined $self->{BITMAPS}) {
        return $self->dumpsection4($data, $descriptors, $width);
    }

    # $Show_all_operators must be turned off for this sub to work correctly
    _croak "Cannot dump section 4 properly with bitmaps"
        . " when Show_all_operators is set" if $Show_all_operators;

    # The kind of bit maps (i.e. the operator descriptors) used in BUFR message
    my @bitmap_desc = @{ $self->{BITMAP_OPERATORS} };

    my @bitmap_array; # Will contain for each bit map a reference to a hash with
                      # key: index (in data and descriptor arrays) for data value
                      # value: index for bit mapped value

    # For compressed data all subsets use same bit map (we assume)
    $isub = 0 if $self->{COMPRESSED_DATA};

    my $txt = "\n";
    my $space = ' ';
    my $line = $space x (17 + $width);
    foreach my $bitmap_num (0..$#bitmap_desc) {
        $line .= "  $bitmap_desc[$bitmap_num]";
        # Convert the sequence of ($data_idesc,$bitmapped_idesc) pairs into a hash
        my %hash = @{ $self->{BITMAPS}->[$bitmap_num + 1]->[$isub] };
        $bitmap_array[$bitmap_num] = \%hash;
    }
    # First make a line showing the operator descriptors using bit maps
    $txt .= "$line\n";

    my $B_table = $self->{B_TABLE};
    # Add the artificial descriptor for associated field
    $B_table->{999999} = "ASSOCIATED FIELD\0Numeric";
    my $C_table = $self->{C_TABLE} || '';

    my $idx = 0;
    # Loop over data descriptors
  ID:
    foreach my $id (@{$descriptors}) {
        # Stop printing when the bit map part starts
        last ID if (substr($id,0,1) eq '2'
                        and ($id =~ /^22[2-5]/ || $id =~ /^232/));

        # Get the data value
        my $value = defined $data->[$idx] ? $data->[$idx] : 'missing';
        _croak "Data descriptor $id is not present in BUFR table B"
            unless exists $B_table->{$id};
        my ($name, $unit, $bits) = (split /\0/, $B_table->{$id})[0,1,4];
        $line = sprintf "%6d  %06d  %${width}.${width}s ",
            $idx+1, $id, $value;

        # Then get the corresponding bit mapped values, using '*******'
        # if 'data not present' in bit map
        my $max_len = 7;
        foreach my $bitmap_num (0..$#bitmap_desc) {
            my $val;
            if ($bitmap_array[$bitmap_num]->{$idx}) {
                # data marked as 'data present' in bitmap
                my $bitmapped_idesc = $bitmap_array[$bitmap_num]->{$idx};
                $val = defined $data->[$bitmapped_idesc]
                    ? $data->[$bitmapped_idesc] : 'missing';
                $max_len = length($val) if length($val) > $max_len;
            } else {
                $val = '*******';
            }
            # If $max_len has been increased, this might not always
            # print very pretty, but at least there is no truncation
            # of digits in value
            $line .= sprintf " %${max_len}.${max_len}s", $val;
        }
        # Code or flag table number equals $id, so no need to display this in [unit]
        my $short_unit = $unit;
        my $unit_start = uc(substr($unit, 0, 4));
        if ($unit_start eq 'CODE') {
            $short_unit = 'CODE TABLE';
        } elsif ($unit_start eq 'FLAG') {
            $short_unit = 'FLAG TABLE';
        }
        $line .=  sprintf "  %s\n", "$name [$short_unit]";
        $txt .= $line;

        # Check for illegal flag value
        if ($Strict_checking && $short_unit eq 'FLAG TABLE' && $bits > 1) {
            if ($value ne 'missing' and $value % 2) {
                my $max_value = 2**$bits - 1;
                $bits += 0; # get rid of spaces
                _complain("$id - $value: rightmost bit $bits is set indicating missing value"
                          . " but then value should be $max_value");
            }
        }

        # Resolve flag and code table values if code table is loaded
        if ($C_table && $value ne 'missing') {
            my $num_spaces = $width + 19 + 7*@bitmap_desc;
            $txt .= _get_code_table_txt($id,$value,$unit,$B_table,$C_table,$num_spaces)
        }
        $idx++;
    }
    return $txt;
}

## Return the text found in flag or code tables for value $value of
## descriptor $id. The empty string is returned if $unit is neither
## CODE TABLE nor FLAG TABLE, or if $unit is CODE TABLE but for this
## $value there is no text in C table. Returns a "... does not exist!"
## message if flag/code table is not found. If $check_illegal is
## defined, an 'Illegal value' message is returned if $value is bigger
## than allowed or has highest bit set without having all other bits
## set.
sub _get_code_table_txt {
    my ($id,$value,$unit,$B_table,$C_table,$num_spaces,$check_illegal) = @_;

    my $txt = '';
    # Need case insensitive matching, since local tables from at least
    # DWD use 'Code table', not 'CODE TABLE', in the ECMWF ecCodes
    # distribution
    if ($unit =~ m/^CODE[ ]?TABLE/i) {
        my $code_table = sprintf "%06d", $id;
        return "Code table $code_table does not exist!\n"
            if ! exists $C_table->{$code_table};
        if ($C_table->{$code_table}{$value}) {
            my @lines = split "\n", $C_table->{$code_table}{$value};
            foreach (@lines) {
                $txt .= sprintf "%s   %s\n", ' ' x ($num_spaces), lc $_;
            }
        }
    } elsif ($unit =~ m/^FLAG[ ]?TABLE/i) {
        my $flag_table = sprintf "%06d", $id;
        return "Flag table $flag_table does not exist!\n"
            if ! exists $C_table->{$flag_table};

        my $width = (split /\0/, $B_table->{$flag_table})[4];
        $width += 0;            # Get rid of spaces
        # Cannot handle more than 32 bits flags with current method
        _croak "Unable to handle > 32 bits flag; $id has width $width"
            if $width > 32;

        my $max_value = 2**$width - 1;

        if (defined $check_illegal and $value > $max_value) {
            $txt = "Illegal value: $value is bigger than maximum allowed ($max_value)\n";
        } elsif ($value == $max_value) {
            $txt = sprintf "%s=> %s", ' ' x ($num_spaces), "bit $width set:"
                . sprintf "%s   %s\n", ' ' x ($num_spaces), "missing value\n";
        } else {
            # Convert to bitstring and localize the 1 bits
            my $binary = pack "N", $value; # Packed as 32 bits in big-endian order
            my $bitstring = substr unpack('B*',$binary), 32-$width;
            for my $i (1..$width) {
                if (substr($bitstring, $i-1, 1) == 1) {
                    $txt .= sprintf "%s=> %s", ' ' x ($num_spaces),
                        "bit $i set";
                    if ($C_table->{$flag_table}{$i}) {
                        my @lines = split "\n", $C_table->{$flag_table}{$i};
                        $txt .= ': ' . lc (shift @lines) . "\n";
                        foreach (@lines) {
                            $txt .= sprintf "%s   %s\n", ' ' x ($num_spaces), lc $_;
                        }
                    } else {
                        $txt .= "\n";
                    }
                }
            }
            if (defined $check_illegal and $txt =~ /bit $width set/) {
                $txt = "Illegal value ($value): bit $width is set indicating missing value,"
                    . " but then value should be $max_value\n";
            }
        }
    }
    return $txt;
}

##  Convert from integer to descriptor
sub _int2fxy {
    my @fxy = map {sprintf("%1d%02d%03d", ($_>>14)&0x3, ($_>>8)&0x3f, $_&0xff)} @_;
    return @_ > 1 ? @fxy : $fxy[0];
}

##  Expand a list of descriptors using BUFR table D, also expanding
##  simple replication but not delayed replication
sub _expand_descriptors {
    my $D_table = shift;
    my @expanded = ();

    for (my $di = 0; $di < @_; $di++) {
        my $descriptor = $_[$di];
        _croak "$descriptor is not a BUFR descriptor"
            if $descriptor !~ /^\d{6}$/;
        my $f = int substr($descriptor, 0, 1);
        if ($f == 1) {
            my $x = substr $descriptor, 1, 2; # Replicate next $x descriptors
            my $y = substr $descriptor, 3;    # Number of replications
            if ($y > 0) {
                # Simple replication (replicate next x descriptors y times)
                _croak "Cannot expand: Not enough descriptors following "
                    . "replication descriptor $descriptor (or there is "
                    . "a problem in nesting of replication)" if $di+$x+1 > @_;
                my @r = ();
                push @r, @_[($di+1)..($di+$x)] for (1..$y);
                # Recursively expand replicated descriptors $y times
                my @s = ();
                @s = _expand_descriptors($D_table, @r) if @r;
                if ($Show_replication) {
                    # Adjust x since replicated descriptors might have been expanded
                    # Unfortunately _spew is not available here to report the x>99 -> x=0 hack
                    my $z =  @s/$y > 99 ? 0 : @s/$y;
                    substr($_[$di], 1, 2) = sprintf "%02d", $z;
                    push @expanded, $_[$di];
                }
                push @expanded, @s if @s;
                $di += $x;
            } else {
                # Delayed replication. Next descriptor ought to be the
                # delayed descriptor replication (and data repetition)
                # factor, i.e. one of 0310(00|01|02|11|12), followed
                # by the x descriptors to be replicated
                if ($di+2 == @_ && $_[$di+1] =~ /^0310(00|01|02|11|12)$/) {
                    _complain "Missing the $x descriptors which should follow"
                        . " $descriptor $_[$di+1]";
                    push @expanded, @_[$di,$di+1];
                    last;
                }
                _croak "Cannot expand: Not enough descriptors following delayed"
                    . " replication descriptor $descriptor (or there is "
                    . "a problem in nesting of replication)" if $di+$x+1 > @_;
                _croak "Cannot expand: Delayed replication descriptor "
                    . "$descriptor is not followed by one of "
                    . "0310(00|01|02|11|12) but by $_[$di+1]"
                        if $_[$di+1] !~ /^0310(00|01|02|11|12)$/;
                my @r = @_[($di+2)..($di+$x+1)];
                # Here we just expand the D descriptors in the
                # descriptors to be replicated. The final expansion
                # using delayed replication factor has to wait until
                # data part is decoded
                my @s = ();
                @s = _expand_descriptors($D_table, @r) if @r;
                # Must adjust x since replicated descriptors might have been expanded
                substr($_[$di], 1, 2) = sprintf "%02d", scalar @s;
                push @expanded, @_[$di,$di+1], @s;
                $di += 1+$x; # NOTE: 1 is added to $di on next iteration
            }
            next;
        } elsif ($f == 3) {
            _croak "No sequence descriptor $descriptor in BUFR table D"
                if not exists $D_table->{$descriptor};
            # Expand recursively, if necessary
            push @expanded,
                _expand_descriptors($D_table, split /\s/, $D_table->{$descriptor});
        } else { # f=0,2
            push @expanded, $descriptor;
        }
    }

    return @expanded;
}

## Return a text string suitable for printing information about the given
## BUFR table descriptors
##
## $how = 'fully': Expand all D descriptors fully into B descriptors,
## with name, unit, scale, reference value and width (each on a
## numbered line, except for replication operators which are not
## numbered).
##
## $how = 'partially': Like 'fully, but expand D descriptors only once
## and ignore replication.
##
## $how = 'noexpand': Like 'partially', but do not expand D
## descriptors at all.
##
## $how = 'simply': Like 'partially', but list the descriptors on one
## single line with no extra information provided.
sub resolve_descriptor {
    my $self = shift;
    my $how = shift;
    foreach (@_) {
        _croak("'$_' is not an integer argument to resolve_descriptor!")
            unless /^\d+$/;
    }
    my @desc = map { sprintf "%06d", $_ } @_;

    my @allowed_hows = qw( simply fully partially noexpand );
    _croak "First argument in resolve_descriptor must be one of"
        . " '@allowed_hows', is: '$how'"
            unless grep { $how eq $_ } @allowed_hows;

    if (! $self->{B_TABLE}) {
        if ($BUFR_table{FORMAT} eq 'ECCODES' && $self->{LOCAL_TABLES_NOT_FOUND}) {
            _croak "Local table " . $self->{LOCAL_TABLES_NOT_FOUND} . " couldn't be found,"
                . " or you might need to load WMO master table also?";
        } else {
            _croak "No B table is loaded - did you forget to call load_BDtables?";
        }
    }
    my $B_table = $self->{B_TABLE};

    # Some local tables are provided only for element descriptors, and
    # we might in fact not need the sequence descriptors for resolving
    my $D_table;
    my $need_Dtable = 0;
    foreach my $id (@desc) {
        if (substr($id,0,1) eq '3') {
            $need_Dtable = 1;
        }
    }
    if ($need_Dtable && ! $self->{D_TABLE}) {
        if ($BUFR_table{FORMAT} eq 'ECCODES' && $self->{LOCAL_TABLES_NOT_FOUND}) {
            _croak "Local table " . $self->{LOCAL_TABLES_NOT_FOUND} . " couldn't be found,"
                . " or you might need to load WMO master table also?";
        } else {
            _croak "No D table is loaded - did you forget to call load_BDtables?";
        }
    } else {
        # Could consider omitting this if $need_Dtable = 0 ...
        $D_table = $self->{D_TABLE};
    }

    my $txt = '';

    if ($how eq 'simply' or $how eq 'partially') {
        my @expanded;
        foreach my $id (@desc) {
            my $f = substr $id, 0, 1;
            if ($f == 3) {
                _croak "$id is not in table D, unable to expand"
                    unless $D_table->{$id};
                push @expanded, split /\s/, $D_table->{$id};
            } else {
                push @expanded, $id;
            }
        }
        if ($how eq 'simply') {
            return $txt = "@expanded\n";
        } else {
            @desc = @expanded;
        }
    }
    if ($how eq 'fully') {
        if (@desc == 1 and $desc[0] =~ /^1/) {
            # This is simply a replication descriptor; do not try to expand
        } else {
            @desc = _expand_descriptors($D_table, @desc);
        }
    }

    my $count = 0;
    foreach my $id (@desc) {
        if ($id =~ /^[123]/) {
            $txt .= sprintf "    %06d\n", $id;
        } elsif ($B_table->{$id}) {
            my ($name,$unit,$scale,$refval,$width) = split /\0/, $B_table->{$id};
            $txt .= sprintf "%3d %06d  %s [%s] %d %d %d\n",
                ++$count,$id,$name,$unit,$scale,$refval,$width;
        } else {
            $txt .= sprintf "%3d %06d  Not in table B\n",
                ++$count,$id;
        }
    }
    return $txt;
}

## Return BUFR table B information for an element descriptor for the
## last table loaded, as an array of name, unit, scale, reference
## value and data width in bits. Returns false if the descriptor is
## not found or no data width is defined, or croaks if no table B has
## been loaded.
sub element_descriptor {
    my $self = shift;
    my $desc = shift;
    _croak "Argument to element_descriptor must be an integer\n"
        unless $desc =~ /^\d+$/;
    $desc = sprintf "%06d", $desc;
    _croak "No BUFR B table loaded\n" unless defined $self->{B_TABLE};
    return unless defined $self->{B_TABLE}->{$desc};
    my ($name, $unit, $scale, $refval, $width)
        = split /\0/, $self->{B_TABLE}->{$desc};
    return unless defined $width && $width =~ /\d+$/;
    return ($name, $unit, $scale+0, $refval+0, $width+0);
}

## Return BUFR table D information for a sequence descriptor for the
## last table loaded, as a space separated string of the descriptors
## in the direct (nonrecursive) lookup in table D. Returns false if
## the sequence descriptor is not found, or croaks if no table D has
## been loaded.
sub sequence_descriptor {
    my $self = shift;
    my $desc = shift;
    _croak "Argument to element_descriptor must be an integer\n"
        unless $desc =~ /^\d+$/;
    _croak "No BUFR D table loaded\n" unless defined $self->{D_TABLE};
    return unless defined $self->{D_TABLE}->{$desc};
    if (wantarray) {
        return split / /, $self->{D_TABLE}->{$desc};
    } else {
        return $self->{D_TABLE}->{$desc};
    }
}

## Return a text string telling which bits are set and the meaning of
## the bits set when $value is interpreted as a flag value, also
## checking for illegal values. The empty string is returned if $value=0.
sub resolve_flagvalue {
    my $self = shift;
    my ($value, $flag_table, $table, $num_leading_spaces) = @_;
    _croak "Flag value can't be negative!\n" if $value < 0;
    $num_leading_spaces ||= 0;  # Default value

    $self->load_Ctable($table);
    my $C_table = $self->{C_TABLE};

    # Number of bits used for the flag is hard to extract from C
    # table; it is much easier to obtain from B table
    $self->load_BDtables($table);
    my $B_table = $self->{B_TABLE};

    my $unit = 'FLAG TABLE';
    return _get_code_table_txt($flag_table,$value,$unit,
                               $B_table,$C_table,$num_leading_spaces,'check_illegal');
}

## Return the contents of code table $code_table, or empty string if
## code table is not found
sub dump_codetable {
    my $self = shift;
    my ($code_table, $table) = @_;
    _croak("code_table '$code_table' is not a (positive) integer in dump_codetable()")
        unless $code_table =~ /^\d+$/;
    $code_table = sprintf "%06d", $code_table;

    $self->load_Ctable($table);
    my $C_table = $self->{C_TABLE};

    return '' unless $C_table->{$code_table};

    my $dump;
    foreach my $value (sort {$a <=> $b} keys %{ $C_table->{$code_table} }) {
        my $txt = $C_table->{$code_table}{$value};
        chomp $txt;
        $txt =~ s/\n/\n       /g;
        $dump .= sprintf "%3d -> %s\n", $value, $txt;
    }
    return $dump;
}

## Decode bitstream (data part of section 4) while working through the
## (expanded) descriptors in section 3. The final data and
## corresponding descriptors are put in $self->{DATA} and
## $self->{DESC} (indexed by subset number)
sub _decode_bitstream {
    my $self = shift;
    $self->{CODING} = 'DECODE';
    my $bitstream = $self->{SEC4_RAWDATA} . "\0\0\0\0";
    my $maxpos = 8*length($self->{SEC4_RAWDATA});
    my $pos = 0;
    my @operators;
    my $ref_values_ref; # Hash ref to reference values with descriptors as keys;
                        # to be implemented later (not used yet)
    my @subset_data; # Will contain data values for subset 1,2...
    my @subset_desc; # Will contain the set of descriptors for subset 1,2...
                     # expanded to be in one to one correspondance with the data
    my $repeat_X; # Set to number of descriptors to be repeated if
                  # delayed descriptor and data repetition factor is
                  # in effect
    my $repeat_factor; # Set to number of times descriptors (and data)
                       # are to be repeated if delayed descriptor and
                       # data repetition factor is in effect
    my @repeat_desc; # The descriptors to be repeated
    my @repeat_data; # The data to be repeated
    my $B_table = $self->{B_TABLE};

    # Has to fully expand @desc for each subset in turn, as delayed
    # replication factors might be different for each subset,
    # resulting in different full expansions. During the expansion the
    # effect of operator descriptors are taken into account, causing
    # most of them to be eliminated (unless $Show_all_operators is
    # set), so that @desc and the equivalent $subset_desc[$isub] ends
    # up being in one to one correspondence with the data values in
    # $subset_data[$isub] (the operators included having data value
    # '')
  S_LOOP: foreach my $isub (1..$self->{NUM_SUBSETS}) {
        $self->_spew(2, "Decoding subset number %d", $isub) if $Spew;

        # Bit maps might vary from subset to subset, so must be rebuilt
        undef $self->{BITMAP_OPERATORS};
        undef $self->{BITMAP_START};
        undef $self->{REUSE_BITMAP};
        $self->{NUM_BITMAPS} = 0;
        $self->{BACKWARD_DATA_REFERENCE} = 1;
        $self->{NUM_CHANGE_OPERATORS} = 0;

        my @desc = split /\s/, $self->{DESCRIPTORS_EXPANDED};

        # Note: @desc as well as $idesc may be changed during this loop,
        # so we cannot use a foreach loop instead
      D_LOOP: for (my $idesc = 0; $idesc < @desc; $idesc++) {
            my $id = $desc[$idesc];
            my $f = substr($id,0,1);
            my $x = substr($id,1,2)+0;
            my $y = substr($id,3,3)+0;

            if ($f == 1) {
                if ($Show_replication) {
                    push @{$subset_desc[$isub]}, $id;
                    push @{$subset_data[$isub]}, '';
                    $self->_spew(4, "X=0 in $id for F=1, might have been > 99 in expansion")
                        if $Spew && $x == 0;
                }
                next D_LOOP if $y > 0; # Nothing more to do for normal replication

                if ($x == 0) {
                    _complain("Nonsensical replication of zero descriptors ($id)");
                    $idesc++;
                    next D_LOOP;
                }

                $_ = $desc[$idesc+1];
                _croak "$id Erroneous replication factor"
                    unless /^0310(00|01|02|11|12)/ && exists $B_table->{$_};

                my $width = (split /\0/, $B_table->{$_})[-1];
                my $factor = bitstream2dec($bitstream, $pos, $width);
                $pos += $width;
                # Delayed descriptor replication factors (and
                # associated fields) are the only values in section 4
                # where all bits being 1 is not to be interpreted as a
                # missing value
                if (not defined $factor) {
                    $factor = 2**$width - 1;
                }
                if ($Spew) {
                    if ($_ eq '031011' || $_ eq '031012') {
                        $self->_spew(4, "$_  Delayed repetition factor: %s", $factor);
                    } else {
                        $self->_spew(4, "$_  Delayed replication factor: %s", $factor);
                    }
                }
                # Include the delayed replication in descriptor and data list
                splice @desc, $idesc++, 0, $_;
                push @{$subset_desc[$isub]}, $_;
                push @{$subset_data[$isub]}, $factor;

                if ($_ eq '031011' || $_ eq '031012') {
                    # For delayed repetition, descriptor *and* data are
                    # to be repeated
                    $repeat_X = $x;
                    $repeat_factor = $factor;
                }
                my @r = ();
                push @r, @desc[($idesc+2)..($idesc+$x+1)] while $factor--;
                splice @desc, $idesc, 2+$x, @r;

                if ($repeat_factor) {
                    # Skip to the last set to be repeated, which will
                    # then be included $repeat_factor times
                    $idesc += $x * ($repeat_factor - 1);
                    $self->_spew(4, "Delayed repetition ($id $_ -> @r)") if $Spew;
                } else {
                    $self->_spew(4, "Delayed replication ($id $_ -> @r)") if $Spew;
                }
                if ($idesc < @desc) {
                    redo D_LOOP;
                } else {
                    last D_LOOP; # Might happen if delayed factor is 0
                }

            } elsif ($f == 2) {
                my $flow;
                my $bm_idesc;
                ($pos, $flow, $bm_idesc, @operators)
                    = $self->_apply_operator_descriptor($id, $x, $y, $pos, $isub,
                                                        $desc[$idesc+1], @operators);
                if ($flow eq 'redo_bitmap') {
                    # Data value is associated with the descriptor
                    # defined by bit map. Remember original and new
                    # index in descriptor array for the bit mapped
                    # values ('dr' = data reference)
                    my $dr_idesc;
                    if (!defined $bm_idesc) {
                        $dr_idesc = shift @{$self->{REUSE_BITMAP}->[$isub]};
                    } elsif (!$Show_all_operators) {
                        $dr_idesc = $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                            + $bm_idesc;
                    } else {
                        $dr_idesc = $self->{BITMAP_START}[$self->{NUM_BITMAPS}];
                        # Skip operator descriptors
                        while ($bm_idesc-- > 0) {
                            $dr_idesc++;
                            $dr_idesc++ while ($desc[$dr_idesc] >= 200000);
                        }
                    }
                    push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[$isub] },
                         $dr_idesc, $idesc;
                    if ($Show_all_operators) {
                        push @{$subset_desc[$isub]}, $id;
                        push @{$subset_data[$isub]}, '';
                    }
                    $desc[$idesc] = $desc[$dr_idesc];
                    redo D_LOOP;
                } elsif ($flow eq 'signify_character') {
                    push @{$subset_desc[$isub]}, $id;
                    # Extract ASCII string
                    my $value = bitstream2ascii($bitstream, $pos, $y);
                    $pos += 8*$y;
                    # Trim string, also removing nulls
                    $value = _trim($value, $id);
                    push @{$subset_data[$isub]}, $value;
                    next D_LOOP;
                } elsif ($flow eq 'no_value') {
                    # Some operator descriptors ought to be included
                    # in expanded descriptors even though they have no
                    # corresponding data value, because they contain
                    # valuable information to be displayed in
                    # dumpsection4 (e.g. 222000 'Quality information follows')
                    push @{$subset_desc[$isub]}, $id;
                    push @{$subset_data[$isub]}, '';
                    next D_LOOP;
                }

                if ($Show_all_operators) {
                    push @{$subset_desc[$isub]}, $id;
                    push @{$subset_data[$isub]}, '';
                } else {
                    # Remove operator descriptor from @desc
                    splice @desc, $idesc--, 1;
                }

                next D_LOOP if $flow eq 'next';
                last D_LOOP if $flow eq 'last';
                if ($flow eq 'skip') {
                    $idesc++;
                    next D_LOOP;
                }
            }

            if ($self->{CHANGE_REFERENCE_VALUE}) {
                # The data descriptor is to be associated with a new
                # reference value, which is fetched from data stream
                _croak "Change reference operator 203Y is not followed by element"
                    . " descriptor, but $id" if $f > 0;
                my $num_bits = $self->{CHANGE_REFERENCE_VALUE};
                my $new_refval = bitstream2dec($bitstream, $pos, $num_bits);
                $pos += $num_bits;
                # Negative value if most significant bit is set (one's complement)
                $new_refval = $new_refval & (1<<$num_bits-1)
                    ? -($new_refval & ((1<<$num_bits-1)-1))
                        : $new_refval;
                $self->_spew(4, "$id * Change reference value: ".
                             ($new_refval > 0 ? "+" : "")."$new_refval") if $Spew;
                $self->{NEW_REFVAL_OF}{$id}{$isub} = $new_refval;
                # Identify new reference values by setting f=9
                push @{$subset_desc[$isub]}, $id + 900000;
                push @{$subset_data[$isub]}, $new_refval;
                next D_LOOP;
            }

            # If operator 204$y 'Add associated field is in effect',
            # each data value is preceded by $y bits which should be
            # decoded separately. We choose to provide a descriptor
            # 999999 in this case (like the ECMWF BUFRDC software)
            if ($self->{ADD_ASSOCIATED_FIELD} and $id ne '031021') {
                # First extract associated field
                my $width = $self->{ADD_ASSOCIATED_FIELD};
                my $value = bitstream2dec($bitstream, $pos, $width);
                # All bits set to 1 for associated field is NOT
                # interpreted as missing value
                $value = 2**$width - 1 if ! defined $value;
                $pos += $width;
                push @{$subset_desc[$isub]}, 999999;
                push @{$subset_data[$isub]}, $value;
                $self->_spew(4, "Added associated field: %s", $value) if $Spew;
            }

            # We now have a "real" data descriptor
            push @{$subset_desc[$isub]}, $id;

            # For quality information, if this relates to a bit map we
            # need to store index of the data ($data_idesc) for which
            # the quality information applies, as well as the new
            # index ($idesc) in the descriptor array for the bit
            # mapped values
            if (substr($id,0,3) eq '033'
                && defined $self->{BITMAP_OPERATORS}
                && $self->{BITMAP_OPERATORS}->[-1] eq '222000') {
                if (defined $self->{REUSE_BITMAP}) {
                    my $data_idesc = shift @{ $self->{REUSE_BITMAP}->[$isub] };
                    _croak "$id: Not enough quality values provided"
                        if not defined $data_idesc;
                    push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[$isub] },
                         $data_idesc, $idesc;
                } else {
                    my $data_idesc = shift @{ $self->{CURRENT_BITMAP} };
                    _croak "$id: Not enough quality values provided"
                        if not defined $data_idesc;
                    push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[$isub] },
                         $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                             + $data_idesc, $idesc;
                }
            }

            # Find the relevant entry in BUFR table B
            _croak "Data descriptor $id is not present in BUFR table B"
                unless exists $B_table->{$id};
            my ($name,$unit,$scale,$refval,$width) = split /\0/, $B_table->{$id};
            $self->_spew(3, "%6s  %-20s  %s", $id, $unit, $name) if $Spew;

            # Override Table B values if Data Description Operators are in effect
            if ($self->{NUM_CHANGE_OPERATORS} > 0) {
                if ($unit ne 'CCITTIA5' && $unit !~ /^(CODE|FLAG)/) {
                    if (defined $self->{CHANGE_SRW}) {
                        $scale += $self->{CHANGE_SRW};
                        $width += int((10*$self->{CHANGE_SRW}+2)/3);
                        $refval *= 10*$self->{CHANGE_SRW};
                    } else {
                        $scale += $self->{CHANGE_SCALE} if defined $self->{CHANGE_SCALE};
                        $width += $self->{CHANGE_WIDTH} if defined $self->{CHANGE_WIDTH};
                    }
                } elsif ($unit eq 'CCITTIA5' && defined $self->{CHANGE_CCITTIA5_WIDTH}) {
                    $width = $self->{CHANGE_CCITTIA5_WIDTH}
                }
                # To prevent autovivification (see perldoc -f exists) we
                # need this laborious test for defined
                $refval = $self->{NEW_REFVAL_OF}{$id}{$isub} if defined $self->{NEW_REFVAL_OF}{$id}
                    && defined $self->{NEW_REFVAL_OF}{$id}{$isub};
                # Difference statistical values use different width and reference value
                if ($self->{DIFFERENCE_STATISTICAL_VALUE}) {
                    $width += 1;
                    $refval = -2**$width;
                    undef $self->{DIFFERENCE_STATISTICAL_VALUE};
                    $self->{NUM_CHANGE_OPERATORS}--;
                }
            }
            _croak "$id Data width <= 0" if $width <= 0;

            my $value;
            if ($unit eq 'CCITTIA5') {
                # Extract ASCII string
                _croak "Width for unit CCITTIA5 must be integer bytes\n"
                    . "is $width bits for descriptor $id" if $width % 8;
                $value = bitstream2ascii($bitstream, $pos, $width/8);
                $self->_spew(3, "  %s", defined $value ? $value : 'missing') if $Spew;
                # Trim string, also removing nulls
                $value = _trim($value, $id);
            } else {
                $value = bitstream2dec($bitstream, $pos, $width);
                if (defined $value) {
                    # Compute and format decoded value
                    ($scale) = $scale =~ /(-?\d+)/; # untaint
                    $value = $scale <= 0 ? ($value + $refval)/10**$scale
                        : sprintf "%.${scale}f", ($value + $refval)/10**$scale;
                }
                $self->_spew(3, "  %s", defined $value ? $value : 'missing') if $Spew;
            }
            $pos += $width;
            push @{$subset_data[$isub]}, $value;
            # $value = undef if missing value

            if ($repeat_X) {
                # Delayed repetition factor (030011/030012) is in
                # effect, so descriptors and data are to be repeated
                push @repeat_desc, $id;
                push @repeat_data, $value;
                if (--$repeat_X == 0) {
                    # Store $repeat_factor repetitions of data and descriptors
                    # (one repetition has already been included)
                    while (--$repeat_factor) {
                        push @{$subset_desc[$isub]}, @repeat_desc;
                        push @{$subset_data[$isub]}, @repeat_data;
                    }
                    @repeat_desc = ();
                    @repeat_data = ();
                }
            }

            if ($id eq '031031' and $self->{BUILD_BITMAP}) {
                # Store the index of expanded descriptors if data is
                # marked as present in data present indicator: 0 is
                # 'present', 1 (undef value) is 'not present'. E.g.
                # bitmap = 1100110 => (2,3,6) is stored in $self->{CURRENT_BITMAP}
                if (defined $value) {
                    push @{$self->{CURRENT_BITMAP}}, $self->{BITMAP_INDEX};
                }
                $self->{BITMAP_INDEX}++;
                if ($self->{BACKWARD_DATA_REFERENCE} == $self->{NUM_BITMAPS}) {
                    my $numb = $self->{NUM_BITMAPS};
                    if (!defined $self->{BITMAP_START}[$numb]) {
                        # Look up the element descriptor immediately
                        # preceding the bitmap operator
                        my $i = $idesc;
                        $i-- while ($desc[$i] ne $self->{BITMAP_OPERATORS}->[-1]
                                    && $i >=0);
                        $i-- while ($desc[$i] > 100000 && $i >=0);
                        _croak "No element descriptor preceding bitmap" if $i < 0;
                        $self->{BITMAP_START}[$numb] = $i;
                    } else {
                        $self->{BITMAP_START}[$numb]--;
                        _croak "Bitmap too big"
                            if $self->{BITMAP_START}[$numb] < 0;
                    }
                }
            } elsif ($self->{BUILD_BITMAP} and $self->{BITMAP_INDEX} > 0) {
                # We have finished building the bit map
                $self->{BUILD_BITMAP} = 0;
                $self->{BITMAP_INDEX} = 0;
                if ($self->{BACKWARD_DATA_REFERENCE} != $self->{NUM_BITMAPS}) {
                    $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                        = $self->{BITMAP_START}[$self->{BACKWARD_DATA_REFERENCE}];
                }
            }
        } # End D_LOOP
    } # END S_LOOP

    # Check that length of section 4 corresponds to what expected from section 3
    $self->_check_section4_length($pos,$maxpos);

    $self->{DATA} = \@subset_data;
    $self->{DESC} = \@subset_desc;
    return;
}

## Decode bitstream (data part of section 4 encoded using BUFR
## compression) while working through the (expanded) descriptors in
## section 3. The final data and corresponding descriptors are put in
## $self->{DATA} and $self->{DESC} (the data indexed by subset number)
sub _decompress_bitstream {
    my $self = shift;
    $self->{CODING} = 'DECODE';
    my $bitstream = $self->{SEC4_RAWDATA}."\0\0\0\0";
    my $nsubsets = $self->{NUM_SUBSETS};
    my $B_table = $self->{B_TABLE};
    my $maxpos = 8*length($self->{SEC4_RAWDATA});
    my $pos = 0;
    my @operators;
    my @subset_data;     # Will contain data values for subset 1,2...,
                         # i.e. $subset[$i] is a reference to an array
                         # containing the data values for subset $i
    my @desc_exp;        # Will contain the set of descriptors for one
                         # subset, expanded to be in one to one
                         # correspondance with the data, i.e. element
                         # descriptors only
    my $repeat_X; # Set to number of descriptors to be repeated if
                  # delayed descriptor and data repetition factor is
                  # in effect. Will be decremented while (repeated)
                  # data sets are extracted
    my $repeat_XX; # Like $repeat_X, but will not be decremented
    my $repeat_factor; # Set to number of times descriptors (and data)
                       # are to be repeated if delayed descriptor and
                       # data repetition factor is in effect
    my @repeat_desc; # The descriptors to be repeated
    my @repeat_data; # The data to be repeated (reference to an array
                     # containing the data values for subset $i)

    _complain("Compression set in section 1 for one subset message")
        if $nsubsets == 1;

    $#subset_data = $nsubsets;

    my @desc = split /\s/, $self->{DESCRIPTORS_EXPANDED};
    # This will be further expanded to be in one to one correspondance
    # with the data, taking replication and table C operators into account

    # All subsets in a compressed BUFR message must have exactly the same
    # fully expanded section 3, i.e. all replications factors must be the same
    # in all subsets. So, as opposed to noncompressed messages, it is enough
    # to run through the set of descriptors once.
  D_LOOP: for (my $idesc = 0; $idesc < @desc; $idesc++) {
        my $id = $desc[$idesc];
        my $f = substr($id,0,1);
        my $x = substr($id,1,2)+0;
        my $y = substr($id,3,3)+0;

        if ($f == 1) {
            if ($Show_replication) {
                push @desc_exp, $id;
                foreach my $isub (1..$nsubsets) {
                    push @{$subset_data[$isub]}, '';
                }
                $self->_spew(4, "X=0 in $id for F=1, might have been > 99 in expansion")
                    if $Spew && $x == 0;
            }
            next D_LOOP if $y > 0; # Nothing more to do for normal replication

            if ($x == 0) {
                _complain("Nonsensical replication of zero descriptors ($id)");
                $idesc++;
                next D_LOOP;
            }

            $_ = $desc[$idesc+1];
            _croak "$id Erroneous replication factor"
                unless /^0310(00|01|02|11|12)/ && exists $B_table->{$_};

            my $width = (split /\0/, $B_table->{$_})[-1];
            my $factor = bitstream2dec($bitstream, $pos, $width);
            $pos += $width + 6; # 6 bits for the bit count (which we
                                # skip because we know it has to be 0
                                # for delayed replication)
            # Delayed descriptor replication factors (and associated
            # fields) are the only values in section 4 where all bits
            # being 1 is not interpreted as a missing value
            if (not defined $factor) {
                $factor = 2**$width - 1;
            }
            # Include the delayed replication in descriptor and data list
            push @desc_exp, $_;
            splice @desc, $idesc++, 0, $_;
            foreach my $isub (1..$nsubsets) {
                push @{$subset_data[$isub]}, $factor;
            }

            if ($_ eq '031011' || $_ eq '031012') {
                # For delayed repetition, descriptor *and* data is
                # to be repeated
                $repeat_X = $repeat_XX = $x;
                $repeat_factor = $factor;
                $self->_spew(4, "$_  Delayed repetition factor: $factor") if $Spew;
            } else {
                $self->_spew(4, "$_  Delayed replication factor: $factor") if $Spew;
            }
            my @r = ();
            push @r, @desc[($idesc+2)..($idesc+$x+1)] while $factor--;
            splice @desc, $idesc, 2+$x, @r;
            if ($Spew) {
                if ($repeat_factor) {
                    $self->_spew(4, "$_  Delayed repetition ($id $_ -> @r)");
                } else {
                    $self->_spew(4, "$_  Delayed replication ($id $_ -> @r)");
                }
            }

            if ($idesc < @desc) {
                redo D_LOOP;
            } else {
                last D_LOOP; # Might happen if delayed factor is 0
            }

        } elsif ($f == 2) {
            my $flow;
            my $bm_idesc;
            ($pos, $flow, $bm_idesc, @operators)
                = $self->_apply_operator_descriptor($id, $x, $y, $pos, 0,
                                                    $desc[$idesc+1], @operators);
            if ($flow eq 'redo_bitmap') {
                # Data value is associated with the descriptor
                # defined by bit map. Remember original and new
                # index in descriptor array for the bit mapped
                # values ('dr' = data reference)
                my $dr_idesc;
                if (!defined $bm_idesc) {
                    $dr_idesc = shift @{ $self->{REUSE_BITMAP}->[0] };
                } elsif (!$Show_all_operators) {
                    $dr_idesc = $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                        + $bm_idesc;
                } else {
                    $dr_idesc = $self->{BITMAP_START}[$self->{NUM_BITMAPS}];
                    # Skip operator descriptors
                    while ($bm_idesc-- > 0) {
                        $dr_idesc++;
                        $dr_idesc++ while ($desc[$dr_idesc] >= 200000);
                    }
                }
                push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[0] },
                     $dr_idesc, $idesc;
                if ($Show_all_operators) {
                    push @desc_exp, $id;
                    foreach my $isub (1..$nsubsets) {
                        push @{$subset_data[$isub]}, '';
                    }
                }
                $desc[$idesc] = $desc[$dr_idesc];
                redo D_LOOP;
            } elsif ($flow eq 'signify_character') {
                push @desc_exp, $id;
                $pos = $self->_extract_compressed_value($id, $idesc, $pos, $bitstream,
                                                $nsubsets, \@subset_data);
                next D_LOOP;
            } elsif ($flow eq 'no_value') {
                # Some operator descriptors ought to be included
                # in expanded descriptors even though they have no
                # corresponding data value, because they contain
                # valuable information to be displayed in
                # dumpsection4 (e.g. 222000 'Quality information follows')
                push @desc_exp, $id;
                foreach my $isub (1..$nsubsets) {
                    push @{$subset_data[$isub]}, '';
                }
                next D_LOOP;
            }

            if ($Show_all_operators) {
                push @desc_exp, $id;
                foreach my $isub (1..$nsubsets) {
                    push @{$subset_data[$isub]}, '';
                }
            } else {
                # Remove operator descriptor from @desc
                splice @desc, $idesc--, 1;
            }

            next D_LOOP if $flow eq 'next';
            last D_LOOP if $flow eq 'last';
            if ($flow eq 'skip') {
                $idesc++;
                next D_LOOP;
            }
        }

        if ($self->{CHANGE_REFERENCE_VALUE}) {
            # The data descriptor is to be associated with a new
            # reference value, which is fetched from data stream
            _croak "Change reference operator 203Y is not followed by element"
                . " descriptor, but $id" if $f > 0;
            my $num_bits = $self->{CHANGE_REFERENCE_VALUE};
            my $new_refval = bitstream2dec($bitstream, $pos, $num_bits);
            $pos += $num_bits + 6;
            # Negative value if most significant bit is set (one's complement)
            $new_refval = $new_refval & (1<<$num_bits-1)
                ? -($new_refval & ((1<<$num_bits-1)-1))
                    : $new_refval;
            $self->_spew(4, "$id * Change reference value: ".
                         ($new_refval > 0 ? "+" : "")."$new_refval") if $Spew;
            $self->{NEW_REFVAL_OF}{$id} = $new_refval;
            # Identify new reference values by setting f=9
            push @desc_exp, $id + 900000;
            foreach my $isub (1..$nsubsets) {
                push @{$subset_data[$isub]}, $new_refval;
            }
            next D_LOOP;
        }

        # If operator 204$y 'Add associated field is in effect',
        # each data value is preceded by $y bits which should be
        # decoded separately. We choose to provide a descriptor
        # 999999 in this case (like the ECMWF BUFRDC software)
        if ($self->{ADD_ASSOCIATED_FIELD} and $id ne '031021') {
            # First extract associated field
            push @desc_exp, 999999;
            $pos = $self->_extract_compressed_value(999999, $idesc, $pos, $bitstream,
                                                    $nsubsets, \@subset_data);
        }

        # We now have a "real" data descriptor, so add it to the descriptor list
        push @desc_exp, $id;

        $pos = $self->_extract_compressed_value($id, $idesc, $pos, $bitstream,
                                                $nsubsets, \@subset_data, \@desc);
        if ($repeat_X) {
            # Delayed repetition factor (030011/030012) is in
            # effect, so descriptors and data are to be repeated
            push @repeat_desc, $id;
            foreach my $isub (1..$nsubsets) {
                push @{$repeat_data[$isub]}, $subset_data[$isub]->[-1];
            }
            if (--$repeat_X == 0) {
                # Store $repeat_factor repetitions of data and descriptors
                # (one repetition has already been included)
                while (--$repeat_factor) {
                    push @desc_exp, @repeat_desc;
                    foreach my $isub (1..$nsubsets) {
                        push @{$subset_data[$isub]}, @{$repeat_data[$isub]};
                    }
                    $idesc += $repeat_XX;
                }
                @repeat_desc = ();
                @repeat_data = ();
                $repeat_XX = 0;
            }
        }
    }

    # Check that length of section 4 corresponds to what expected from section 3
    $self->_check_section4_length($pos,$maxpos);

    $self->{DATA} = \@subset_data;
    $self->{DESC} = \@desc_exp;
    return;
}

## Extract the data values for descriptor $id (with index $idesc in
## the final expanded descriptor array) for each subset, into
## $subset_data_ref->[$isub], $isub = 1...$nsubsets (number of
## subsets). Extraction starts at position $pos in $bitstream.
sub _extract_compressed_value {
    my $self = shift;
    my ($id, $idesc, $pos, $bitstream, $nsubsets, $subset_data_ref, $desc_ref) = @_;
    my $B_table = $self->{B_TABLE};

    # For quality information, if this relates to a bit map we
    # need to store index of the data ($data_idesc) for which
    # the quality information applies, as well as the new
    # index ($idesc) in the descriptor array for the bit
    # mapped values
    if (substr($id,0,3) eq '033'
        && defined $self->{BITMAP_OPERATORS}
        && $self->{BITMAP_OPERATORS}->[-1] eq '222000') {
        if (defined $self->{REUSE_BITMAP}) {
            my $data_idesc = shift @{ $self->{REUSE_BITMAP}->[0] };
            _croak "$id: Not enough quality values provided"
                if not defined $data_idesc;
            push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[0] },
                 $data_idesc, $idesc;
        } else {
            my $data_idesc = shift @{ $self->{CURRENT_BITMAP} };
            _croak "$id: Not enough quality values provided"
                if not defined $data_idesc;
            push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[0] },
                 $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                     + $data_idesc, $idesc;
        }
    }

    # Find the relevant entry in BUFR table B
    my ($name,$unit,$scale,$refval,$width);
    if ($id == 999999) {
        $name = 'ASSOCIATED FIELD';
        $unit = 'NUMERIC';
        $scale = 0;
        $refval = 0;
        $width = $self->{ADD_ASSOCIATED_FIELD};
    } elsif ($id =~ /^205(\d\d\d)/) { # Signify character
        $name = 'CHARACTER INFORMATION';
        $unit = 'CCITTIA5';
        $scale = 0;
        $refval = 0;
        $width = 8*$1;
    } else {
        _croak "Data descriptor $id is not present in BUFR table B"
            if not exists $B_table->{$id};
        ($name,$unit,$scale,$refval,$width) = split /\0/, $B_table->{$id};

        # Override Table B values if Data Description Operators are in effect
        if ($self->{NUM_CHANGE_OPERATORS} > 0) {
            if ($unit ne 'CCITTIA5' && $unit !~ /^(CODE|FLAG)/) {
                if (defined $self->{CHANGE_SRW}) {
                    $scale += $self->{CHANGE_SRW};
                    $width += int((10*$self->{CHANGE_SRW}+2)/3);
                    $refval *= 10*$self->{CHANGE_SRW};
                } else {
                    $scale += $self->{CHANGE_SCALE} if defined $self->{CHANGE_SCALE};
                    $width += $self->{CHANGE_WIDTH} if defined $self->{CHANGE_WIDTH};
                }
            } elsif ($unit eq 'CCITTIA5' && defined $self->{CHANGE_CCITTIA5_WIDTH}) {
                $width = $self->{CHANGE_CCITTIA5_WIDTH}
            }
            $refval = $self->{NEW_REFVAL_OF}{$id} if defined $self->{NEW_REFVAL_OF}{$id};
            # Difference statistical values use different width and reference value
            if ($self->{DIFFERENCE_STATISTICAL_VALUE}) {
                $width += 1;
                $refval = -2**$width;
                undef $self->{DIFFERENCE_STATISTICAL_VALUE};
                $self->{NUM_CHANGE_OPERATORS}--;
            }
        }
    }
    $self->_spew(3, "%6s  %-20s   %s", $id, $unit, $name) if $Spew;
    _croak "$id Data width <= 0" if $width <= 0;

    if ($unit eq 'CCITTIA5') {
        # Extract ASCII string ('minimum value')
        _croak "Width for unit CCITTIA5 must be integer bytes\n"
            . "is $width bits for descriptor $id" if $width % 8;
        my $minval = bitstream2ascii($bitstream, $pos, $width/8);
        if ($Spew) {
            if ($minval eq "\0" x ($width/8)) {
                $self->_spew(5, " Local reference value has all bits zero");
            } else {
                $self->_spew(5, " Local reference value: %s", $minval);
            }
        }
        $pos += $width;
        # Extract number of bytes for next subsets
        my $deltabytes = bitstream2dec($bitstream, $pos, 6);
        $self->_spew(5, " Increment width (bytes): %d", $deltabytes) if $Spew;
        $pos += 6;
        if ($deltabytes && defined $minval) {
            # Extract compressed data for all subsets. According
            # to 94.6.3 (2) (i) in FM 94 BUFR, the first value for
            # character data shall be set to all bits zero
            my $nbytes = $width/8;
            _complain("Local reference value for compressed CCITTIA5 data "
                      . "hasn't all bits set to zero, but is '$minval'")
                if $Strict_checking and $minval ne "\0" x $nbytes;
            my $incr_values;
            foreach my $isub (1..$nsubsets) {
                my $string = bitstream2ascii($bitstream, $pos, $deltabytes);
                if ($Spew) {
                    $incr_values .= defined $string ? "$string," : ',';
                }
                # Trim string, also removing nulls
                $string = _trim($string, $id);
                push @{$subset_data_ref->[$isub]}, $string;
                $pos += 8*$deltabytes;
            }
            if ($Spew) {
                chop $incr_values;
                $self->_spew(5, " Increment values: %s", $incr_values);
            }
        } else {
            # If min value is defined => All subsets set to min value
            # If min value is undefined => Data in all subsets are undefined
            my $value = defined $minval ? $minval : undef;
            # Trim string, also removing nulls
            $value = _trim($value, $id);
            foreach my $isub (1..$nsubsets) {
                push @{$subset_data_ref->[$isub]}, $value;
            }
            $pos += $nsubsets*8*$deltabytes;
        }
        $self->_spew(3, "  %s", join ',',
             map { defined($subset_data_ref->[$_][-1]) ?
                 $subset_data_ref->[$_][-1] : 'missing'} 1..$nsubsets) if $Spew;
    } else {
        # Extract minimum value
        my $minval = bitstream2dec($bitstream, $pos, $width);
        $minval += $refval if defined $minval;
        $pos += $width;
        $self->_spew(5, " Local reference value: %d", $minval) if $Spew && defined $minval;

        # Extract number of bits for next subsets
        my $deltabits = bitstream2dec($bitstream, $pos, 6);
        $pos += 6;
        $self->_spew(5, " Increment width (bits): %d", $deltabits) if $Spew;

        if ($deltabits && defined $minval) {
            # Extract compressed data for all subsets
            my $incr_values;
            foreach my $isub (1..$nsubsets) {
                my $value = bitstream2dec($bitstream, $pos, $deltabits);
                _complain("value " . ($value + $minval) . " in subset $isub for "
                          . "$id too big to be encoded without compression")
                    if ($Strict_checking && defined $value &&
                        ($value + $minval) > 2**$width);
                $incr_values .= defined $value ? "$value," : ',' if $Spew;
                if (defined $value) {
                    # Compute and format decoded value
                    ($scale) = $scale =~ /(-?\d+)/; # untaint
                    $value = $scale <= 0 ? ($value + $minval)/10**$scale
                        : sprintf "%.${scale}f", ($value + $minval)/10**$scale;
                }
                # All bits set to 1 for associated field is NOT
                # interpreted as missing value
                if ($id == 999999 and ! defined $value) {
                    $value = 2**$width - 1;
                }
                push @{$subset_data_ref->[$isub]}, $value;
                $pos += $deltabits;
            }
            if ($Spew) {
                chop $incr_values;
                $self->_spew(5, " Increment values: %s", $incr_values);
            }
        } else {
            # If minimum value is defined => All subsets set to minimum value
            # If minimum value is undefined => Data in all subsets are undefined
            my $value;
            if (defined $minval) {
                # Compute and format decoded value
                ($scale) = $scale =~ /(-?\d+)/; # untaint
                $value = $scale <= 0 ? $minval/10**$scale
                    : sprintf "%.${scale}f", $minval/10**$scale;
            }
            # Exception: all bits set to 1 for associated field is NOT
            # interpreted as missing value
            if ($id == 999999 and ! defined $value) {
                $value = 2**$width - 1;
            }
            foreach my $isub (1..$nsubsets) {
                push @{$subset_data_ref->[$isub]}, $value;
            }
            $pos += $nsubsets*$deltabits if defined $deltabits;
        }

        # Bit maps need special treatment. We are only able to
        # handle those where all subsets have exactly the same
        # bit map with the present method.
        if ($id eq '031031' and $self->{BUILD_BITMAP}) {
            _croak "$id: Unable to handle bit maps which differ between subsets"
                . " in compressed data" if $deltabits;
            # Store the index of expanded descriptors if data is
            # marked as present in data present indicator: 0 is
            # 'present', 1 (undef value) is 'not present'
            if (defined $minval) {
                push @{$self->{CURRENT_BITMAP}}, $self->{BITMAP_INDEX};
            }
            $self->{BITMAP_INDEX}++;
            if ($self->{BACKWARD_DATA_REFERENCE} == $self->{NUM_BITMAPS}) {
                my $numb = $self->{NUM_BITMAPS};
                if (!defined $self->{BITMAP_START}[$numb]) {
                    # Look up the element descriptor immediately
                    # preceding the bitmap operator
                    my $i = $idesc;
                    $i-- while ($desc_ref->[$i] ne $self->{BITMAP_OPERATORS}->[-1]
                                && $i >=0);
                    $i-- while ($desc_ref->[$i] > 100000 && $i >=0);
                    _croak "No element descriptor preceding bitmap" if $i < 0;
                    $self->{BITMAP_START}[$numb] = $i;
                } else {
                    if ($Show_all_operators) {
                        my $i = $self->{BITMAP_START}[$numb] - 1;
                        $i-- while ($desc_ref->[$i] > 100000 && $i >=0);
                        $self->{BITMAP_START}[$numb] = $i;
                    } else {
                        $self->{BITMAP_START}[$numb]--;
                    }
                    _croak "Bitmap too big"
                        if $self->{BITMAP_START}[$numb] < 0;
                }
            }
        } elsif ($self->{BUILD_BITMAP} and $self->{BITMAP_INDEX} > 0) {
            # We have finished building the bit map
            $self->{BUILD_BITMAP} = 0;
            $self->{BITMAP_INDEX} = 0;
            if ($self->{BACKWARD_DATA_REFERENCE} != $self->{NUM_BITMAPS}) {
                $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                    = $self->{BITMAP_START}[$self->{BACKWARD_DATA_REFERENCE}];
            }
        }
        $self->_spew(3, "  %s", join ' ',
             map { defined($subset_data_ref->[$_][-1]) ?
                 $subset_data_ref->[$_][-1] : 'missing'} 1..$nsubsets) if $Spew;
    }
    return $pos;
}

## Takes a text $decoded_message as argument and returns BUFR messages
## which would give the same output as $decoded_message when running
## dumpsection0(), dumpsection1(), dumpsection3() and dumpsection4() in
## turn on each of the reencoded BUFR messages
sub reencode_message {
    my $self = shift;
    my $decoded_message = shift;
    my $width = shift || 15;    # Optional argument
    # Data values usually start at column 31, but if a $width
    # different from 15 was used in dumpsection4 you should use the
    # same value here

    my @lines = split /\n/, $decoded_message;
    my $bufr_messages = '';
    my $i = 0;

  MESSAGE: while ($i < @lines) {
        # Some tidying after decoding of previous message might be
        # necessary
        $self->{NUM_CHANGE_OPERATORS} = 0;
        undef $self->{CHANGE_WIDTH};
        undef $self->{CHANGE_CCITTIA5_WIDTH};
        undef $self->{CHANGE_SCALE};
        undef $self->{CHANGE_REFERENCE_VALUE};
        undef $self->{NEW_REFVAL_OF};
        undef $self->{CHANGE_SRW};
        undef $self->{ADD_ASSOCIATED_FIELD};
        undef $self->{BITMAPS};
        undef $self->{BITMAP_OPERATORS};
        undef $self->{REUSE_BITMAP};
        $self->{NUM_BITMAPS} = 0;
        # $self->{LOCAL_USE} is always set for BUFR edition < 4 in _encode_sec1
        undef $self->{LOCAL_USE};

        # Extract section 0 info
        $i++ while $lines[$i] !~ /^Section 0/ and $i < @lines-1;
        last MESSAGE if $i >= @lines-1; # Not containing any decoded BUFR message
        $i++; # Skip length of BUFR message
        ($self->{BUFR_EDITION}) = $lines[++$i]
            =~ /BUFR edition:\s+(\d+)/;
        _croak "BUFR edition number not provided or is not a number"
            unless defined $self->{BUFR_EDITION};

        # Extract section 1 info
        $i++ while $lines[$i] !~ /^Section 1/;
        _croak "reencode_message: Don't find decoded section 1" if $i >= @lines;
        $i++; # Skip length of section 1
        if ($self->{BUFR_EDITION} < 4 ) {
            ($self->{MASTER_TABLE}) = $lines[++$i]
                =~ /BUFR master table:\s+(\d+)/;
            ($self->{SUBCENTRE}) = $lines[++$i]
                =~ /Originating subcentre:\s+(\d+)/;
            ($self->{CENTRE}) = $lines[++$i]
                =~ /Originating centre:\s+(\d+)/;
            ($self->{UPDATE_NUMBER}) = $lines[++$i]
                =~ /Update sequence number:\s+(\d+)/;
            ($self->{OPTIONAL_SECTION}) = $lines[++$i]
                =~ /Optional section present:\s+(\d+)/;
            ($self->{DATA_CATEGORY}) = $lines[++$i]
                =~ /Data category \(table A\):\s+(\d+)/;
            ($self->{DATA_SUBCATEGORY}) = $lines[++$i]
                =~ /Data subcategory:\s+(\d+)/;
            ($self->{MASTER_TABLE_VERSION}) = $lines[++$i]
                =~ /Master table version number:\s+(\d+)/;
            ($self->{LOCAL_TABLE_VERSION}) = $lines[++$i]
                =~ /Local table version number:\s+(\d+)/;
            ($self->{YEAR_OF_CENTURY}) = $lines[++$i]
                =~ /Year of century:\s+(\d+)/;
            ($self->{MONTH}) = $lines[++$i]
                =~ /Month:\s+(\d+)/;
            ($self->{DAY}) = $lines[++$i]
                =~ /Day:\s+(\d+)/;
            ($self->{HOUR}) = $lines[++$i]
                =~ /Hour:\s+(\d+)/;
            ($self->{MINUTE}) = $lines[++$i]
                =~ /Minute:\s+(\d+)/;
            _croak "reencode_message: Something seriously wrong in decoded section 1"
                unless defined $self->{MINUTE};
        } elsif ($self->{BUFR_EDITION} == 4) {
            ($self->{MASTER_TABLE}) = $lines[++$i]
                =~ /BUFR master table:\s+(\d+)/;
            ($self->{CENTRE}) = $lines[++$i]
                =~ /Originating centre:\s+(\d+)/;
            ($self->{SUBCENTRE}) = $lines[++$i]
                =~ /Originating subcentre:\s+(\d+)/;
            ($self->{UPDATE_NUMBER}) = $lines[++$i]
                =~ /Update sequence number:\s+(\d+)/;
            ($self->{OPTIONAL_SECTION}) = $lines[++$i]
                =~ /Optional section present:\s+(\d+)/;
            ($self->{DATA_CATEGORY}) = $lines[++$i]
                =~ /Data category \(table A\):\s+(\d+)/;
            ($self->{INT_DATA_SUBCATEGORY}) = $lines[++$i]
                =~ /International data subcategory:\s+(\d+)/;
            ($self->{LOC_DATA_SUBCATEGORY}) = $lines[++$i]
                =~ /Local data subcategory:\s+(\d+)/;
            ($self->{MASTER_TABLE_VERSION}) = $lines[++$i]
                =~ /Master table version number:\s+(\d+)/;
            ($self->{LOCAL_TABLE_VERSION}) = $lines[++$i]
                =~ /Local table version number:\s+(\d+)/;
            ($self->{YEAR}) = $lines[++$i]
                =~ /Year:\s+(\d+)/;
            ($self->{MONTH}) = $lines[++$i]
                =~ /Month:\s+(\d+)/;
            ($self->{DAY}) = $lines[++$i]
                =~ /Day:\s+(\d+)/;
            ($self->{HOUR}) = $lines[++$i]
                =~ /Hour:\s+(\d+)/;
            ($self->{MINUTE}) = $lines[++$i]
                =~ /Minute:\s+(\d+)/;
            ($self->{SECOND}) = $lines[++$i]
                =~ /Second:\s+(\d+)/;
            _croak "reencode_message: Something seriously wrong in decoded section 1"
                unless defined $self->{SECOND};
        }

        # Extract section 3 info
        $i++ while $lines[$i] !~ /^Section 3/;
        _croak "reencode_message: Don't find decoded section 3" if $i >= @lines;
        $i++; # Skip length of section 3

        ($self->{NUM_SUBSETS}) = $lines[++$i]
            =~ /Number of data subsets:\s+(\d+)/;
        _croak "Don't support reencoding of 0 subset message"
            if $self->{NUM_SUBSETS} == 0;
        ($self->{OBSERVED_DATA}) = $lines[++$i]
            =~ /Observed data:\s+(\d+)/;
        ($self->{COMPRESSED_DATA}) = $lines[++$i]
            =~ /Compressed data:\s+(\d+)/;
        ($self->{DESCRIPTORS_UNEXPANDED}) = $lines[++$i]
            =~ /Data descriptors unexpanded:\s+(\d+.*)/;
        _croak "reencode_message: Something seriously wrong in decoded section 3"
            unless defined $self->{DESCRIPTORS_UNEXPANDED};

        # Extract data values to use in section 4
        my ($data_refs, $desc_refs);
        my $subset = 0;
      SUBSET: while ($i < @lines-1) {
            $_ = $lines[++$i];
            next SUBSET if /^$/ or /^Subset/;
            last SUBSET if /^Message/;
            $_ = substr $_, 0, $width + 16;
            s/^\s+//;
            next SUBSET if not /^\d/;
            my ($n, $desc, $value) = split /\s+/, $_, 3;
            $subset++ if $n == 1;
            if (defined $value) {
                $value =~ s/\s+$//;
                $value = undef if $value eq '' or $value eq 'missing';
            } else {
                # Some descriptors are not numbered (like 222000)
                $desc = $n;
                $value = '';
            }
            push @{$data_refs->[$subset]}, $value;
            push @{$desc_refs->[$subset]}, $desc;
        }

        # If optional section is present, pretend it is not, because we
        # are not able to encode this section
        if ($self->{OPTIONAL_SECTION}) {
            $self->{OPTIONAL_SECTION} = 0;
            carp "Warning: 'Optional section present' changed from 1 to 0'\n";
        }

        $bufr_messages .= $self->encode_message($data_refs, $desc_refs);
    }

    return $bufr_messages;
}


## Encode a new BUFR message. All relevant metadata
## ($self->{BUFR_EDITION} etc) must have been initialized already or
## else the _encode_sec routines will croak.
sub encode_message {
    my $self = shift;
    my ($data_refs, $desc_refs) = @_;

    _croak "encode_message: No data/descriptors provided" unless $desc_refs;

    $self->{MESSAGE_NUMBER}++;
    $self->_spew(2, "Encoding message number %d", $self->{MESSAGE_NUMBER}) if $Spew;

    $self->load_BDtables();

    $self->_spew(2, "Encoding section 1-3") if $Spew;
    my $sec1_stream = $self->_encode_sec1();
    my $sec2_stream = $self->_encode_sec2();
    my $sec3_stream = $self->_encode_sec3();
    $self->_spew(2, "Encoding section 4") if $Spew;
    my $sec4_stream = $self->_encode_sec4($data_refs, $desc_refs);

    # Compute length of whole message and encode section 0
    my $msg_len = 8 + length($sec1_stream) + length($sec2_stream)
        + length($sec3_stream) + length($sec4_stream) + 4;
    my $msg_len_binary = pack("N", $msg_len);
    my $bufr_edition_binary = pack('n', $self->{BUFR_EDITION});
    my $sec0_stream = 'BUFR' . substr($msg_len_binary,1,3)
                             . substr($bufr_edition_binary,1,1);

    my $new_message = $sec0_stream . $sec1_stream . $sec2_stream
        . $sec3_stream  . $sec4_stream  . '7777';
    return $new_message;
}

## Encode and return section 1
sub _encode_sec1 {
    my $self = shift;

    my $bufr_edition = $self->{BUFR_EDITION} or
        _croak "_encode_sec1: BUFR edition not defined";

    my @keys = qw( MASTER_TABLE  CENTRE  SUBCENTRE  UPDATE_NUMBER
                   OPTIONAL_SECTION  DATA_CATEGORY  MASTER_TABLE_VERSION
                   LOCAL_TABLE_VERSION  MONTH  DAY  HOUR  MINUTE );
    if ($bufr_edition < 4) {
        push @keys, qw( DATA_SUBCATEGORY  YEAR_OF_CENTURY );
    } elsif ($bufr_edition == 4) {
        push @keys, qw( INT_DATA_SUBCATEGORY  LOC_DATA_SUBCATEGORY  YEAR  SECOND );
    }

    # Check that the required variables for section 1 are provided
    foreach my $key (@keys) {
        _croak "_encode_sec1: $key not given"
            unless defined $self->{$key};
    }

    $self->_validate_datetime() if ($Strict_checking);

    my $sec1_stream;
    # Byte 4-
    if ($bufr_edition < 4) {
        $self->{LOCAL_USE} = "\0" if !defined $self->{LOCAL_USE};
        $sec1_stream = pack 'C14a*',
            $self->{MASTER_TABLE},
            $self->{SUBCENTRE},
            $self->{CENTRE},
            $self->{UPDATE_NUMBER},
            $self->{OPTIONAL_SECTION} ? 128 : 0,
            $self->{DATA_CATEGORY},
            $self->{DATA_SUBCATEGORY},
            $self->{MASTER_TABLE_VERSION},
            $self->{LOCAL_TABLE_VERSION},
            $self->{YEAR_OF_CENTURY},
            $self->{MONTH},
            $self->{DAY},
            $self->{HOUR},
            $self->{MINUTE},
            $self->{LOCAL_USE};
    } elsif ($bufr_edition == 4) {
        $sec1_stream = pack 'CnnC7nC5',
            $self->{MASTER_TABLE},
            $self->{CENTRE},
            $self->{SUBCENTRE},
            $self->{UPDATE_NUMBER},
            $self->{OPTIONAL_SECTION} ? 128 : 0,
            $self->{DATA_CATEGORY},
            $self->{INT_DATA_SUBCATEGORY},
            $self->{LOC_DATA_SUBCATEGORY},
            $self->{MASTER_TABLE_VERSION},
            $self->{LOCAL_TABLE_VERSION},
            $self->{YEAR},
            $self->{MONTH},
            $self->{DAY},
            $self->{HOUR},
            $self->{MINUTE},
            $self->{SECOND};
        $sec1_stream .= pack 'a*', $self->{LOCAL_USE}
            if defined $self->{LOCAL_USE};
    }

    my $sec1_len = 3 + length $sec1_stream;
    if ($bufr_edition < 4) {
        # Each section should be an even number of octets
        if ($sec1_len % 2) {
            $sec1_stream .= "\0";
            $sec1_len++;
        }
    }

    # Byte 1-3
    my $sec1_len_binary = substr pack("N", $sec1_len), 1, 3;

    return $sec1_len_binary . $sec1_stream;
}

## Encode and return section 2 (empty string if no optional section)
sub _encode_sec2 {
    my $self = shift;
    if ($self->{OPTIONAL_SECTION}) {
        _croak "_encode_sec2: No optional section provided"
            unless defined  $self->{SEC2_STREAM};
        return $self->{SEC2_STREAM};
    } else {
        return '';
    }
}

## Encode and return section 3
sub _encode_sec3 {
    my $self = shift;

    # Check that the required variables for section 3 are provided
    foreach my $key (qw(NUM_SUBSETS OBSERVED_DATA COMPRESSED_DATA
                        DESCRIPTORS_UNEXPANDED)) {
        _croak "_encode_sec3: $key not given"
            unless defined $self->{$key};
    }

    my @desc = split / /, $self->{DESCRIPTORS_UNEXPANDED};

    # Byte 5-6
    my $nsubsets_binary = pack "n", $self->{NUM_SUBSETS};

    # Byte 7
    my $flag = pack 'C', $self->{OBSERVED_DATA}*128 +
                         $self->{COMPRESSED_DATA}*64;

    # Byte 8-
    my $desc_binary = "\0\0" x @desc;
    my $pos = 0;
    foreach my $desc (@desc) {
        my $f = substr($desc,0,1);
        my $x = substr($desc,1,2)+0;
        my $y = substr($desc,3,3)+0;
        dec2bitstream($f, $desc_binary, $pos, 2);
        $pos += 2;
        dec2bitstream($x, $desc_binary, $pos, 6);
        $pos += 6;
        dec2bitstream($y, $desc_binary, $pos, 8);
        $pos += 8;
    }

    my $sec3_len = 7 + length $desc_binary;
    if ($self->{BUFR_EDITION} < 4) {
        # Each section should be an even number of octets
        if ($sec3_len % 2) {
            $desc_binary .= "\0";
            $sec3_len++;
        }
    }

    # Byte 1-4
    my $sec3_len_binary = pack("N", $sec3_len);
    my $sec3_start = substr($sec3_len_binary, 1, 3) . "\0";

    return $sec3_start . $nsubsets_binary . $flag . $desc_binary;
}

## Encode and return section 4
sub _encode_sec4 {
    my $self = shift;
    my ($data_refs, $desc_refs) = @_;

    # Check that dimension of argument arrays agrees with number of
    # subsets in section 3
    my $nsubsets = $self->{NUM_SUBSETS};
    _croak "Wrong number of subsets ($nsubsets) in section 3?\n"
        . "Disagrees with dimension of descriptor array used as argument "
            . "to encode_message()"
                unless @$desc_refs == $nsubsets + 1;

    my ($bitstream, $byte_len) = $self->{COMPRESSED_DATA}
        ? $self->_encode_compressed_bitstream($data_refs, $desc_refs)
            : $self->_encode_bitstream($data_refs, $desc_refs);

    my $sec4_len = $byte_len + 4;
    my $sec4_len_binary = pack("N", $sec4_len);
    my $sec4_stream = substr($sec4_len_binary, 1, 3) . "\0" . $bitstream;

    return $sec4_stream;
}

## Encode a nil message, i.e. all values set to missing except delayed
## replication factors and the (descriptor, value) pairs in the hash
## ref $stationid_ref. Delayed replication factors will all be set to
## 1 unless $delayed_repl_ref is provided, in which case the
## descriptors 031001 and 031002 will get the values contained in
## @$delayed_repl_ref. Note that data in section 1 and 3 must have
## been set before calling this method.
sub encode_nil_message {
    my $self = shift;
    my ($stationid_ref, $delayed_repl_ref) = @_;

    _croak "encode_nil_message: No station descriptors provided"
        unless $stationid_ref;

    my $bufr_edition = $self->{BUFR_EDITION} or
        _croak "encode_nil_message: BUFR edition not defined";

    # Since a nil message necessarily is a one subset message, some
    # metadata might need to be adjusted (saving the user for having
    # to remember this)
    $self->set_number_of_subsets(1);
    $self->set_compressed_data(0);

    $self->load_BDtables();

    $self->_spew(2, "Encoding NIL message") if $Spew;
    my $sec1_stream = $self->_encode_sec1();
    my $sec3_stream = $self->_encode_sec3();
    my $sec4_stream = $self->_encode_nil_sec4($stationid_ref,
                                              $delayed_repl_ref);

    # Compute length of whole message and encode section 0
    my $msg_len = 8 + length($sec1_stream) + length($sec3_stream)
        + length($sec4_stream) + 4;
    my $msg_len_binary = pack("N", $msg_len);
    my $bufr_edition_binary = pack('n', $bufr_edition);
    my $sec0_stream = 'BUFR' . substr($msg_len_binary,1,3)
                             . substr($bufr_edition_binary,1,1);

    my $new_message = $sec0_stream . $sec1_stream . $sec3_stream . $sec4_stream
        . '7777';
    return $new_message;
}

## Encode and return section 4 with all values set to missing except
## delayed replication factors and the (descriptor, value) pairs in
## the hash ref $stationid_ref. Delayed replication factors will all
## be set to 1 unless $delayed_repl_ref is provided, in which case the
## descriptors 031001 and 031002 will get the values contained in
## @$delayed_repl_ref (in that order).
sub _encode_nil_sec4 {
    my $self = shift;
    $self->{CODING} = 'ENCODE';
    my ($stationid_ref, $delayed_repl_ref) = @_;
    my @delayed_repl = defined $delayed_repl_ref ? @$delayed_repl_ref : ();

    # Get the expanded list of descriptors (i.e. expanded with table D)
    if (not $self->{DESCRIPTORS_EXPANDED}) {
        _croak "_encode_nil_sec4: DESCRIPTORS_UNEXPANDED not given"
            unless $self->{DESCRIPTORS_UNEXPANDED};
        my @unexpanded = split / /, $self->{DESCRIPTORS_UNEXPANDED};
        _croak "_encode_nil_sec4: D_TABLE not given"
            unless $self->{D_TABLE};
        my $alias = "$self->{TABLE_VERSION} " . $self->{DESCRIPTORS_UNEXPANDED};
        if (exists $Descriptors_already_expanded{$alias}) {
            $self->{DESCRIPTORS_EXPANDED} = $Descriptors_already_expanded{$alias};
        } else {
            $Descriptors_already_expanded{$alias} = $self->{DESCRIPTORS_EXPANDED}
                = join " ", _expand_descriptors($self->{D_TABLE}, @unexpanded);
        }
    }

    # The rest is very similar to sub _decode_bitstream, except that we
    # now are encoding, not decoding a bitstream, with most values set
    # to missing value, and we do not need to fully expand the
    # descriptors.
    my $B_table = $self->{B_TABLE};
    my @operators;
    my $bitstream = chr(255) x 65536; # one bits only
    my $pos = 0;

    my @desc = split /\s/, $self->{DESCRIPTORS_EXPANDED};
  D_LOOP: for (my $idesc = 0; $idesc < @desc; $idesc++) {

        my $id = $desc[$idesc];
        my $f = substr($id,0,1);
        my $x = substr($id,1,2)+0;
        my $y = substr($id,3,3)+0;

        if ($f == 1) {
            # Delayed replication
            if ($x == 0) {
                _complain("Nonsensical replication of zero descriptors ($id)");
                $idesc++;
                next D_LOOP;
            }
            _croak "$id _expand_descriptors() did not do its job"
                if $y > 0;

            $_ = $desc[$idesc+1];
            _croak "$id Erroneous replication factor"
                unless /^0310(00|01|02|11|12)/ && exists $B_table->{$_};
            my $factor = 1;
            if (@delayed_repl && /^03100(1|2)/) {
                $factor = shift @delayed_repl;
                _croak "Delayed replication factor must be positive integer in "
                    . "encode_nil_message, is '$factor'"
                        if ($factor !~ /^\d+$/ || $factor == 0);
            }
            my ($name,$unit,$scale,$refval,$width) = split /\0/, $B_table->{$_};
            if ($Spew) {
                $self->_spew(3, "%6s  %-20s   %s", $id, $unit, $name);
                $self->_spew(3, "  %s", $factor);
            }
            dec2bitstream($factor, $bitstream, $pos, $width);
            $pos += $width;
            # Include the delayed replication in descriptor list
            splice @desc, $idesc++, 0, $_;

            my @r = ();
            push @r, @desc[($idesc+2)..($idesc+$x+1)] while $factor--;
            $self->_spew(4, "Delayed replication ($id $_ -> @r)") if $Spew;
            splice @desc, $idesc, 2+$x, @r;

            if ($idesc < @desc) {
                redo D_LOOP;
            } else {
                last D_LOOP; # Might happen if delayed factor is 0
            }

        } elsif ($f == 2) {
            my $next_id = $desc[$idesc+1];
            my $flow;
            my $bm_idesc;
            ($pos, $flow, $bm_idesc, @operators)
                = $self->_apply_operator_descriptor($id, $x, $y, $pos, 0,
                                                    $next_id, @operators);
            next D_LOOP if $flow eq 'next';
        }

        # We now have a "real" data descriptor

        # Find the relevant entry in BUFR table B
        _croak "Data descriptor $id is not present in BUFR table B"
            unless exists $B_table->{$id};
        my ($name,$unit,$scale,$refval,$width) = split /\0/, $B_table->{$id};
        $self->_spew(3, "%6s  %-20s   %s", $id, $unit, $name) if $Spew;

        # Override Table B values if Data Description Operators are in effect
        if ($self->{NUM_CHANGE_OPERATORS} > 0) {
            if ($unit ne 'CCITTIA5' && $unit !~ /^(CODE|FLAG)/) {
                if (defined $self->{CHANGE_SRW}) {
                    $scale += $self->{CHANGE_SRW};
                    $width += int((10*$self->{CHANGE_SRW}+2)/3);
                    $refval *= 10*$self->{CHANGE_SRW};
                } else {
                    $scale += $self->{CHANGE_SCALE} if defined $self->{CHANGE_SCALE};
                    $width += $self->{CHANGE_WIDTH} if defined $self->{CHANGE_WIDTH};
                }
            } elsif ($unit eq 'CCITTIA5' && defined $self->{CHANGE_CCITTIA5_WIDTH}) {
                $width = $self->{CHANGE_CCITTIA5_WIDTH}
            }
            $refval = $self->{NEW_REFVAL_OF}{$id} if defined $self->{NEW_REFVAL_OF}{$id};
        }
        _croak "$id Data width <= 0" if $width <= 0;

        if ($stationid_ref->{$id}) {
            my $value = $stationid_ref->{$id};
            $self->_spew(3, "  %s", $value) if $Spew;
            if ($unit eq 'CCITTIA5') {
                # Encode ASCII string in $width bits (left justified,
                # padded with spaces)
                my $num_bytes = int($width/8);
                _croak "Ascii string too long to fit in $width bits: $value"
                    if length($value) > $num_bytes;
                $value .= ' ' x ($num_bytes - length($value));
                ascii2bitstream($value, $bitstream, $pos, $num_bytes);
            } else {
                # Encode value as integer in $width bits
                $value = int($value * 10**$scale - $refval + 0.5);
                _croak "Data value no $id is negative: $value"
                    if $value < 0;
                dec2bitstream($value, $bitstream, $pos, $width);
            }
        } else {
            # Missing value is encoded as 1 bits
        }
        $pos += $width;
    }

    # Pad with 0 bits if necessary to get an even or integer number of
    # octets, depending on bufr edition
    my $padnum = $self->{BUFR_EDITION} < 4 ? (16-($pos%16)) % 16 : (8-($pos%8)) % 8;
    if ($padnum > 0) {
        null2bitstream($bitstream, $pos, $padnum);
    }
    my $len = ($pos + $padnum)/8;
    $bitstream = substr $bitstream, 0, $len;

    # Encode section 4
    my $sec4_len_binary = pack("N", $len + 4);
    my $sec4_stream = substr($sec4_len_binary, 1, 3) . "\0" . $bitstream;

    return $sec4_stream;
}

## Encode bitstream using the data values in $data_refs, first
## expanding section 3 fully (and comparing with $desc_refs to check
## for consistency). This sub is very similar to sub _decode_bitstream
sub _encode_bitstream {
    my $self = shift;
    $self->{CODING} = 'ENCODE';
    my ($data_refs, $desc_refs) = @_;

    # Expand section 3 except for delayed replication and operator descriptors
    my @unexpanded = split / /, $self->{DESCRIPTORS_UNEXPANDED};
    my $alias = "$self->{TABLE_VERSION} " . $self->{DESCRIPTORS_UNEXPANDED};
    if (exists $Descriptors_already_expanded{$alias}) {
        $self->{DESCRIPTORS_EXPANDED} = $Descriptors_already_expanded{$alias};
    } else {
        $Descriptors_already_expanded{$alias} = $self->{DESCRIPTORS_EXPANDED}
            = join " ", _expand_descriptors($self->{D_TABLE}, @unexpanded);
    }

    my $nsubsets = $self->{NUM_SUBSETS};
    my $B_table = $self->{B_TABLE};
    my $maxlen = 1024;
    my $bitstream = chr(255) x $maxlen; # one bits only
    my $pos = 0;
    my @operators;

  S_LOOP: foreach my $isub (1..$nsubsets) {
        $self->_spew(2, "Encoding subset number %d", $isub) if $Spew;

        # Bit maps might vary from subset to subset, so must be rebuilt
        undef $self->{BITMAP_OPERATORS};
        undef $self->{BITMAP_START};
        undef $self->{REUSE_BITMAP};
        $self->{NUM_BITMAPS} = 0;
        $self->{BACKWARD_DATA_REFERENCE} = 1;
        $self->{NUM_CHANGE_OPERATORS} = 0;

        # The data values to use for this subset
        my $data_ref = $data_refs->[$isub];
        # The descriptors from expanding section 3
        my @desc = split /\s/, $self->{DESCRIPTORS_EXPANDED};
        # The descriptors to compare with for this subset
        my $desc_ref = $desc_refs->[$isub];

        # Note: @desc as well as $idesc may be changed during this loop,
        # so we cannot use a foreach loop instead
      D_LOOP: for (my $idesc = 0; $idesc < @desc; $idesc++) {
            my $id = $desc[$idesc]
                || _croak("No descriptor no. $idesc defined. Consider using --strict_checking 2"
                          . " or --verbose 4 to explore what went wrong in the encoding");
            my $f = substr($id,0,1);
            my $x = substr($id,1,2)+0;
            my $y = substr($id,3,3)+0;

            if ($f == 1) {
                # Delayed replication
                if ($x == 0) {
                    _complain("Nonsensical replication of zero descriptors ($id)");
                    $idesc++;
                    next D_LOOP;
                }
                _croak "$id _expand_descriptors() did not do its job"
                    if $y > 0;

                my $next_id = $desc[$idesc+1];
                _croak "$id Erroneous replication factor"
                    unless $next_id =~ /^0310(00|01|02|11|12)/ && exists $B_table->{$next_id};
                _croak "Descriptor no $idesc is $desc_ref->[$idesc], expected $next_id"
                    if $desc_ref->[$idesc] != $next_id;
                my $factor = $data_ref->[$idesc];
                my ($name,$unit,$scale,$refval,$width) = split /\0/, $B_table->{$next_id};
                if ($Spew) {
                    $self->_spew(3, "%6s  %-20s  %s", $next_id, $unit, $name);
                    $self->_spew(3, "  %s", $factor);
                }
                ($bitstream, $pos, $maxlen)
                    = $self->_encode_value($factor,$isub,$unit,$scale,$refval,
                                           $width,$next_id,$bitstream,$pos,$maxlen);
                # Include the delayed replication/repetition in descriptor list
                splice @desc, $idesc++, 0, $next_id;

                my @r = ();
                push @r, @desc[($idesc+2)..($idesc+$x+1)] while $factor--;
                splice @desc, $idesc, 2+$x, @r;

                if ($next_id eq '031011' || $next_id eq '031012') {
                    # For delayed repetition we should include data just
                    # once, so skip to the last set in data array
                    $idesc += $x * ($data_ref->[$idesc-1] - 1);
                    # We ought to check that the data sets we skipped are
                    # indeed equal to the last set!
                    $self->_spew(4, "Delayed repetition ($id $next_id -> @r)") if $Spew;
                } else {
                    $self->_spew(4, "Delayed replication ($id $next_id -> @r)") if $Spew;
                }
                if ($idesc < @desc) {
                    redo D_LOOP;
                } else {
                    last D_LOOP; # Might happen if delayed factor is 0
                }

            } elsif ($f == 2) {
                my $flow;
                my $bm_idesc;
                ($pos, $flow, $bm_idesc, @operators)
                    = $self->_apply_operator_descriptor($id, $x, $y, $pos, $isub,
                                                        $desc[$idesc+1], @operators);
                if ($flow eq 'redo_bitmap') {
                    # Data value is associated with the descriptor
                    # defined by bit map. Remember original and new
                    # index in descriptor array for the bit mapped
                    # values ('dr' = data reference)
                    my $dr_idesc;
                    if (!defined $bm_idesc) {
                        $dr_idesc = shift @{ $self->{REUSE_BITMAP}->[$isub]};
                    } elsif (!$Show_all_operators) {
                        $dr_idesc = $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                            + $bm_idesc;
                    } else {
                        $dr_idesc = $self->{BITMAP_START}[$self->{NUM_BITMAPS}];
                        # Skip operator descriptors
                        while ($bm_idesc-- > 0) {
                            $dr_idesc++;
                            $dr_idesc++ while ($desc[$dr_idesc] >= 200000);
                        }
                    }
                    push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[$isub] },
                         $dr_idesc, $idesc;
                    $desc[$idesc] = $desc[$dr_idesc];
                    redo D_LOOP;
                } elsif ($flow eq 'signify_character') {
                    _croak "Descriptor no $idesc is $desc_ref->[$idesc], expected $id"
                        if $desc_ref->[$idesc] != $id;
                    # Get ASCII string
                    my $value = $data_ref->[$idesc];
                    my $name = 'SIGNIFY CHARACTER';
                    my $unit = 'CCITTIA5';
                    my ($scale, $refval, $width) = (0, 0, 8*$y);
                    ($bitstream, $pos, $maxlen)
                        = $self->_encode_value($value,$isub,$unit,$scale,$refval,$width,"205$y",$bitstream,$pos,$maxlen);
                    next D_LOOP;
                } elsif ($flow eq 'no_value') {
                    next D_LOOP;
                }

                # Remove operator descriptor from @desc
                splice @desc, $idesc--, 1;

                next D_LOOP if $flow eq 'next';
                last D_LOOP if $flow eq 'last';
            }

            if ($self->{CHANGE_REFERENCE_VALUE}) {
                # The data descriptor is to be associated with a new
                # reference value, which is fetched from data stream,
                # possibly with f=9 instead of f=0 for descriptor
                $id -= 900000 if $id =~ /^9/;
                _croak "Change reference operator 203Y is not followed by element"
                    . " descriptor, but $id" if $f > 0;
                my $new_refval = $data_ref->[$idesc];
                $self->{NEW_REFVAL_OF}{$id}{$isub} = $new_refval;
                ($bitstream, $pos, $maxlen)
                    = $self->_encode_reference_value($new_refval,$id,$bitstream,$pos,$maxlen);
                next D_LOOP;
            }

            # If operator 204$y 'Add associated field' is in effect,
            # each data value is preceded by $y bits which should be
            # encoded separately. We choose to provide a descriptor
            # 999999 in this case (like the ECMWF BUFRDC software)
            if ($self->{ADD_ASSOCIATED_FIELD} and $id ne '031021') {
                # First encode associated field
                _croak "Descriptor no $idesc is $desc_ref->[$idesc], expected 999999"
                    if $desc_ref->[$idesc] != 999999;
                my $value = $data_ref->[$idesc];
                my $name = 'ASSOCIATED FIELD';
                my $unit = 'NUMERIC';
                my ($scale, $refval) = (0, 0);
                my $width = $self->{ADD_ASSOCIATED_FIELD};
                $self->_spew(4, "Added associated field: %s", $value) if $Spew;
                ($bitstream, $pos, $maxlen)
                    = $self->_encode_value($value,$isub,$unit,$scale,$refval,$width,999999,$bitstream,$pos,$maxlen);
                # Insert the artificial 999999 descriptor for the
                # associated value and increment $idesc to prepare for
                # handling the 'real' value below
                splice @desc, $idesc++, 0, 999999;
            }



            # For quality information, if this relates to a bit map we
            # need to store index of the data ($data_idesc) for which
            # the quality information applies, as well as the new
            # index ($idesc) in the descriptor array for the bit
            # mapped values
            if (substr($id,0,3) eq '033'
                && defined $self->{BITMAP_OPERATORS}
                && $self->{BITMAP_OPERATORS}->[-1] eq '222000') {
                if (defined $self->{REUSE_BITMAP}) {
                    my $data_idesc = shift @{ $self->{REUSE_BITMAP}->[$isub] };
                    _croak "$id: Not enough quality values provided"
                        if not defined $data_idesc;
                    push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[$isub] },
                         $data_idesc, $idesc;
                } else {
                    my $data_idesc = shift @{ $self->{CURRENT_BITMAP} };
                    _croak "$id: Not enough quality values provided"
                        if not defined $data_idesc;
                    push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[$isub] },
                         $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                             + $data_idesc, $idesc;
                }
            }

            my $value = $data_ref->[$idesc];

            if ($id eq '031031' and $self->{BUILD_BITMAP}) {
                # Store the index of expanded descriptors if data is
                # marked as present in data present indicator: 0 is
                # 'present', 1 (undef value) is 'not present'. E.g.
                # bitmap = 1100110 => (2,3,6) is stored in $self->{CURRENT_BITMAP}
                if (defined $value and $value == 0) {
                    push @{$self->{CURRENT_BITMAP}}, $self->{BITMAP_INDEX};
                }
                $self->{BITMAP_INDEX}++;
                if ($self->{BACKWARD_DATA_REFERENCE} == $self->{NUM_BITMAPS}) {
                    my $numb = $self->{NUM_BITMAPS};
                    if (!defined $self->{BITMAP_START}[$numb]) {
                        # Look up the element descriptor immediately
                        # preceding the bitmap operator
                        my $i = $idesc;
                        $i-- while ($desc[$i] ne $self->{BITMAP_OPERATORS}->[-1]
                                    && $i >=0);
                        $i-- while ($desc[$i] > 100000 && $i >=0);
                        _croak "No element descriptor preceding bitmap" if $i < 0;
                        $self->{BITMAP_START}[$numb] = $i;
                    } else {
                        $self->{BITMAP_START}[$numb]--;
                        _croak "Bitmap too big"
                            if $self->{BITMAP_START}[$numb] < 0;
                    }
                }
            } elsif ($self->{BUILD_BITMAP} and $self->{BITMAP_INDEX} > 0) {
                # We have finished building the bit map
                $self->{BUILD_BITMAP} = 0;
                $self->{BITMAP_INDEX} = 0;
                if ($self->{BACKWARD_DATA_REFERENCE} != $self->{NUM_BITMAPS}) {
                    $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                        = $self->{BITMAP_START}[$self->{BACKWARD_DATA_REFERENCE}];
                }
            }

            _croak "Not enough descriptors provided (expected no $idesc to be $id)"
                unless exists $desc_ref->[$idesc];
            _croak "Descriptor no $idesc is $desc_ref->[$idesc], expected $id"
                    if $desc_ref->[$idesc] != $id;

            # Find the relevant entry in BUFR table B
            _croak "Error: Data descriptor $id is not present in BUFR table B"
                unless exists $B_table->{$id};
            my ($name,$unit,$scale,$refval,$width) = split /\0/, $B_table->{$id};
            $refval = $self->{NEW_REFVAL_OF}{$id}{$isub} if defined $self->{NEW_REFVAL_OF}{$id}
                && defined $self->{NEW_REFVAL_OF}{$id}{$isub};
            if ($Spew) {
                $self->_spew(3, "%6s  %-20s  %s", $id, $unit, $name);
                $self->_spew(3, "  %s", defined $value ? $value : 'missing');
            }
########### call to_encode_value inlined for speed
    # Override Table B values if Data Description Operators are in
    # effect (except for associated fields)
    if ($self->{NUM_CHANGE_OPERATORS} > 0 && $id != 999999) {
        if ($unit ne 'CCITTIA5' && $unit !~ /^(CODE|FLAG)/) {
            if (defined $self->{CHANGE_SRW}) {
                $scale += $self->{CHANGE_SRW};
                $width += int((10*$self->{CHANGE_SRW}+2)/3);
                $refval *= 10*$self->{CHANGE_SRW};
            } else {
                $scale += $self->{CHANGE_SCALE} if defined $self->{CHANGE_SCALE};
                $width += $self->{CHANGE_WIDTH} if defined $self->{CHANGE_WIDTH};
            }
        } elsif ($unit eq 'CCITTIA5' && defined $self->{CHANGE_CCITTIA5_WIDTH}) {
            $width = $self->{CHANGE_CCITTIA5_WIDTH}
        }
        _croak "$id Data width is $width which is <= 0" if $width <= 0;
        $refval = $self->{NEW_REFVAL_OF}{$id}{$isub} if defined $self->{NEW_REFVAL_OF}{$id}
        && defined $self->{NEW_REFVAL_OF}{$id}{$isub};
        # Difference statistical values use different width and reference value
        if ($self->{DIFFERENCE_STATISTICAL_VALUE}) {
            $width += 1;
            $refval = -2**$width;
            undef $self->{DIFFERENCE_STATISTICAL_VALUE};
            $self->{NUM_CHANGE_OPERATORS}--;
        }
    }

    # Ensure that bitstream is big enough to encode $value
    while ($pos + $width > $maxlen*8) {
        $bitstream .= chr(255) x $maxlen;
        $maxlen *= 2;
    }

    if (not defined($value)) {
        # Missing value is encoded as 1 bits
        $pos += $width;
    } elsif ($unit eq 'CCITTIA5') {
        # Encode ASCII string in $width bits (left justified,
        # padded with spaces)
        my $num_bytes = int ($width/8);
        _croak "Ascii string too long to fit in $width bits: $value"
            if length($value) > $num_bytes;
        $value .= ' ' x ($num_bytes - length($value));
        ascii2bitstream($value, $bitstream, $pos, $num_bytes);
        $pos += $width;
    } else {
        # Encode value as integer in $width bits
        _croak "Value '$value' is not a number for descriptor $id"
            unless looks_like_number($value);
        $value = int($value * 10**$scale - $refval + 0.5);
        _croak "Encoded data value for $id is negative: $value" if $value < 0;
        my $max_value = 2**$width - 1;
        _croak "Encoded data value for $id is too big to fit in $width bits: $value"
            if $value > $max_value;
        # Check for illegal flag value
        if ($Strict_checking && $unit =~ /^FLAG[ ]?TABLE/ && $width > 1
            && $value < $max_value && $value % 2) {
            _complain("$id - $value: rightmost bit $width is set indicating missing value"
                      . " but then value should be $max_value");
        }
        dec2bitstream($value, $bitstream, $pos, $width);
        $pos += $width;
    }
########### end inlining of_encode_value
        } # End D_LOOP
    } # END S_LOOP




    # Pad with 0 bits if necessary to get an even or integer number of
    # octets, depending on bufr edition
    my $padnum = $self->{BUFR_EDITION} < 4 ? (16-($pos%16)) % 16 : (8-($pos%8)) % 8;
    if ($padnum > 0) {
        null2bitstream($bitstream, $pos, $padnum);
    }
    my $len = ($pos + $padnum)/8;
    $bitstream = substr $bitstream, 0, $len;

    return ($bitstream, $len);
}

sub _encode_reference_value {
    my $self = shift;
    my ($refval,$id,$bitstream,$pos,$maxlen) = @_;

    my $width = $self->{CHANGE_REFERENCE_VALUE};

    # Ensure that bitstream is big enough to encode $value
    while ($pos + $width > $maxlen*8) {
        $bitstream .= chr(255) x $maxlen;
        $maxlen *= 2;
    }

    $self->_spew(4, "Encoding new reference value %d for %6s in %d bits",
                 $refval, $id, $width) if $Spew;
    if ($refval >= 0) {
        _croak "Encoded reference value for $id is too big to fit "
            . "in $width bits: $refval"
                if $refval > 2**$width - 1;
        dec2bitstream($refval, $bitstream, $pos, $width);
    } else {
        # Negative reference values should be encoded by setting first
        # bit to 1 and then encoding absolute value
        _croak "Encoded reference value for $id is too big to fit "
            . "in $width bits: $refval"
                if -$refval > 2**($width-1) - 1;
        dec2bitstream(-$refval, $bitstream, $pos+1, $width-1);
    }
    $pos += $width;

    return ($bitstream, $pos, $maxlen);
}

sub _encode_value {
    my $self = shift;
    my ($value,$isub,$unit,$scale,$refval,$width,$id,$bitstream,$pos,$maxlen) = @_;

    # Override Table B values if Data Description Operators are in
    # effect (except for associated fields)
    if ($self->{NUM_CHANGE_OPERATORS} > 0 && $id != 999999) {
        if ($unit ne 'CCITTIA5' && $unit !~ /^(CODE|FLAG)/) {
            if (defined $self->{CHANGE_SRW}) {
                $scale += $self->{CHANGE_SRW};
                $width += int((10*$self->{CHANGE_SRW}+2)/3);
                $refval *= 10*$self->{CHANGE_SRW};
            } else {
                $scale += $self->{CHANGE_SCALE} if defined $self->{CHANGE_SCALE};
                $width += $self->{CHANGE_WIDTH} if defined $self->{CHANGE_WIDTH};
            }
        } elsif ($unit eq 'CCITTIA5' && defined $self->{CHANGE_CCITTIA5_WIDTH}) {
            $width = $self->{CHANGE_CCITTIA5_WIDTH}
        }
        _croak "$id Data width is $width which is <= 0" if $width <= 0;
        $refval = $self->{NEW_REFVAL_OF}{$id}{$isub} if defined $self->{NEW_REFVAL_OF}{$id}
        && defined $self->{NEW_REFVAL_OF}{$id}{$isub};
        # Difference statistical values use different width and reference value
        if ($self->{DIFFERENCE_STATISTICAL_VALUE}) {
            $width += 1;
            $refval = -2**$width;
            undef $self->{DIFFERENCE_STATISTICAL_VALUE};
            $self->{NUM_CHANGE_OPERATORS}--;
        }
    }

    # Ensure that bitstream is big enough to encode $value
    while ($pos + $width > $maxlen*8) {
        $bitstream .= chr(255) x $maxlen;
        $maxlen *= 2;
    }

    if (not defined($value)) {
        # Missing value is encoded as 1 bits
        $pos += $width;
    } elsif ($unit eq 'CCITTIA5') {
        # Encode ASCII string in $width bits (left justified,
        # padded with spaces)
        my $num_bytes = int ($width/8);
        _croak "Ascii string too long to fit in $width bits: $value"
            if length($value) > $num_bytes;
        $value .= ' ' x ($num_bytes - length($value));
        ascii2bitstream($value, $bitstream, $pos, $num_bytes);
        $pos += $width;
    } else {
        # Encode value as integer in $width bits
        _croak "Value '$value' is not a number for descriptor $id"
            unless looks_like_number($value);
        $value = int($value * 10**$scale - $refval + 0.5);
        _croak "Encoded data value for $id is negative: $value" if $value < 0;
        my $max_value = 2**$width - 1;
        _croak "Encoded data value for $id is too big to fit in $width bits: $value"
            if $value > $max_value;
        # Check for illegal flag value
        if ($Strict_checking && $unit =~ /^FLAG[ ]?TABLE/ && $width > 1
            && $value < $max_value && $value % 2) {
            _complain("$id - $value: rightmost bit $width is set indicating missing value"
                      . " but then value should be $max_value");
        }
        dec2bitstream($value, $bitstream, $pos, $width);
        $pos += $width;
    }

    return ($bitstream, $pos, $maxlen);
}

# Encode reference value using BUFR compression, assuming all subsets
# have same reference value
sub _encode_compressed_reference_value {
    my $self = shift;
    my ($refval,$id,$nsubsets,$bitstream,$pos,$maxlen) = @_;

    my $width = $self->{CHANGE_REFERENCE_VALUE};

    # Ensure that bitstream is big enough to encode $value
    while ($pos + ($nsubsets+1)*$width + 6 > $maxlen*8) {
        $bitstream .= chr(255) x $maxlen;
        $maxlen *= 2;
    }

    $self->_spew(4, "Encoding new reference value %d for %6s in %d bits",
                 $refval, $id, $width) if $Spew;
    # Encode value as integer in $width bits
    if ($refval >= 0) {
        _croak "Encoded reference value for $id is too big to fit "
            . "in $width bits: $refval" if $refval > 2**$width - 1;
        dec2bitstream($refval, $bitstream, $pos, $width);
    } else {
        # Negative reference values should be encoded by setting first
        # bit to 1 and then encoding absolute value
        _croak "Encoded reference value for $id is too big to fit "
            . "in $width bits: $refval" if -$refval > 2**($width-1) - 1;
        dec2bitstream(-$refval, $bitstream, $pos+1, $width-1);
    }
    $pos += $width;

    # Increment width set to 0
    dec2bitstream(0, $bitstream, $pos, 6);
    $pos += 6;

    return ($bitstream, $pos, $maxlen);
}

sub _encode_compressed_value {
    my $self = shift;
    my ($bitstream,$pos,$maxlen,$unit,$scale,$refval,$width,$id,$data_refs,$idesc,$nsubsets) = @_;

    # Override Table B values if Data Description Operators are in
    # effect (except for associated fields)
    if ($self->{NUM_CHANGE_OPERATORS} > 0 && $id != 999999) {
        if ($unit ne 'CCITTIA5' && $unit !~ /^(CODE|FLAG)/) {
            if (defined $self->{CHANGE_SRW}) {
                $scale += $self->{CHANGE_SRW};
                $width += int((10*$self->{CHANGE_SRW}+2)/3);
                $refval *= 10*$self->{CHANGE_SRW};
            } else {
                $scale += $self->{CHANGE_SCALE} if defined $self->{CHANGE_SCALE};
                $width += $self->{CHANGE_WIDTH} if defined $self->{CHANGE_WIDTH};
            }
        } elsif ($unit eq 'CCITTIA5' && defined $self->{CHANGE_CCITTIA5_WIDTH}) {
            $width = $self->{CHANGE_CCITTIA5_WIDTH}
        }
        _croak "$id Data width <= 0" if $width <= 0;
        $refval = $self->{NEW_REFVAL_OF}{$id} if defined $self->{NEW_REFVAL_OF}{$id};
        # Difference statistical values use different width and reference value
        if ($self->{DIFFERENCE_STATISTICAL_VALUE}) {
            $width += 1;
            $refval = -2**$width;
            undef $self->{DIFFERENCE_STATISTICAL_VALUE};
            $self->{NUM_CHANGE_OPERATORS}--;
        }
    }

    # Ensure that bitstream is big enough to encode $value
    while ($pos + ($nsubsets+1)*$width + 6 > $maxlen*8) {
        $bitstream .= chr(255) x $maxlen;
        $maxlen *= 2;
    }

    # Get all values for this descriptor
    my @values;
    my $first_value = $data_refs->[1][$idesc];
    my $all_equal = 1;        # Set to 0 if at least 2 elements differ
    foreach my $value (map { $data_refs->[$_][$idesc] } 2..$nsubsets) {
        if (defined $value && $unit ne 'CCITTIA5' && !looks_like_number($value)) {
            _croak "Value '$value' is not a number for descriptor $id"
        }
        # This used to be a sub (_check_equality), but inlined for speed
        if ($all_equal) {
            if (defined $value && defined $first_value) {
                if ($unit eq 'CCITTIA5') {
                    $all_equal = 0 if $value ne $first_value;
                } else {
                    $all_equal = 0 if $value != $first_value;
                }
            } elsif (defined $value || defined $first_value) {
                $all_equal = 0;
            }
        }
        if (not defined $value) {
            push @values, undef;
        } elsif ($unit eq 'CCITTIA5') {
            push @values, $value;
        } else {
            push @values, int($value * 10**$scale - $refval + 0.5);
        }
        # Check for illegal flag value
        if ($Strict_checking and $unit =~ /^FLAG[ ]?TABLE/ and $width > 1) {
            if (defined $value and $value ne 'missing' and $value % 2) {
                my $max_value = 2**$width - 1;
                _complain("$id - value $value in subset $_:\n"
                          . "rightmost bit $width is set indicating missing value"
                          . " but then value should be $max_value");
            }
        }
    }

    if ($all_equal) {
        # Same value in all subsets. No need to calculate or store increments
        if (defined $first_value) {
            if ($unit eq 'CCITTIA5') {
                # Encode ASCII string in $width bits (left justified,
                # padded with spaces)
                my $num_bytes = int ($width/8);
                _croak "Ascii string too long to fit in $width bits: $first_value"
                    if length($first_value) > $num_bytes;
                $first_value .= ' ' x ($num_bytes - length($first_value));
                ascii2bitstream($first_value, $bitstream, $pos, $num_bytes);
            } else {
                # Encode value as integer in $width bits
                _croak "First value '$first_value' is not a number for descriptor $id"
                    unless looks_like_number($first_value);
                $first_value = int($first_value * 10**$scale - $refval + 0.5);
                _croak "Encoded data value for $id is negative: $first_value"
                    if $first_value < 0;
                _croak "Encoded data value for $id is too big to fit "
                    . "in $width bits: $first_value"
                        if $first_value > 2**$width - 1;
                dec2bitstream($first_value, $bitstream, $pos, $width);
            }
        } else {
            # Missing value is encoded as 1 bits, but bitstream is
            # padded with 1 bits already
        }
        $pos += $width;
        # Increment width set to 0
        dec2bitstream(0, $bitstream, $pos, 6);
        $pos += 6;
    } else {
        if ($unit eq 'CCITTIA5') {
            unshift @values, $first_value;
            # Local reference value set to 0 bits
            null2bitstream($bitstream, $pos, $width);
            $pos += $width;
            # Do not store more characters than needed: remove leading
            # and trailing spaces, then right pad with spaces so that
            # all strings has same length as largest string
            my $largest_length = _trimpad(\@values);
            dec2bitstream($largest_length, $bitstream, $pos, 6);
            $pos += 6;
            # Store the character values
            foreach my $value (@values) {
                if (defined $value) {
                    # Encode ASCII string in $largest_length bytes
                    ascii2bitstream($value, $bitstream, $pos, $largest_length);
                } else {
                    # Missing value is encoded as 1 bits, but
                    # bitstream is padded with 1 bits already
                }
                $pos += $largest_length * 8;
            }
        } else {
            _croak "First value '$first_value' is not a number for descriptor $id"
                if defined($first_value) && !looks_like_number($first_value);
            unshift @values, defined $first_value
                ? int($first_value * 10**$scale - $refval + 0.5)
                    : undef;
            # Numeric data. First find minimum value
            my ($min_value, $isub) = _minimum(\@values);
            _croak "Encoded data value for $id and subset $isub is negative: $min_value"
                if $min_value < 0;
            my @inc_values =
                map { defined $_ ? $_ - $min_value : undef } @values;
            # Find how many bits are required to hold the increment
            # values (or rather: the highest increment value pluss one
            # (except for associated values), to be able to store
            # missing values also)
            my $max_inc = _maximum(\@inc_values);
            my $deltabits = ($id eq '999999')
                ?_get_number_of_bits_to_store($max_inc)
                    : _get_number_of_bits_to_store($max_inc + 1);
            # Store local reference value
            $self->_spew(5, " Local reference value: %d", $min_value) if $Spew;
            dec2bitstream($min_value, $bitstream, $pos, $width);
            $pos += $width;
            # Store increment width
            $self->_spew(5, " Increment width (bits): %d", $deltabits) if $Spew;
            dec2bitstream($deltabits, $bitstream, $pos, 6);
            $pos += 6;
            # Store values
            $self->_spew(5, " Increment values: %s",
                         join(',', map { defined $inc_values[$_]
                         ? $inc_values[$_] : ''} 0..$#inc_values))
                         if $Spew;
            foreach my $value (@inc_values) {
                if (defined $value) {
                    _complain("value " . ($value + $min_value) . " for $id too big"
                              . " to be encoded without compression")
                        if ($Strict_checking && ($value + $min_value) > 2**$width -1);
                    dec2bitstream($value, $bitstream, $pos, $deltabits);
                } else {
                    # Missing value is encoded as 1 bits, but
                    # bitstream is padded with 1 bits already
                }
                $pos += $deltabits;
            }
        }
    }

    return ($bitstream, $pos, $maxlen);
}

## Encode bitstream using the data values in $data_refs, first
## expanding section 3 fully (and comparing with $desc_refs to check
## for consistency). This sub is very similar to sub
## _decompress_bitstream
sub _encode_compressed_bitstream {
    my $self = shift;
    $self->{CODING} = 'ENCODE';
    my ($data_refs, $desc_refs) = @_;

    # Expand section 3 except for delayed replication and operator
    # descriptors. This expansion is the same for all subsets, since
    # delayed replication has to be the same (this needs to be
    # checked) for compression to be possible
    my @unexpanded = split / /, $self->{DESCRIPTORS_UNEXPANDED};
    my $alias = "$self->{TABLE_VERSION} " . $self->{DESCRIPTORS_UNEXPANDED};
    if (exists $Descriptors_already_expanded{$alias}) {
        $self->{DESCRIPTORS_EXPANDED} = $Descriptors_already_expanded{$alias};
    } else {
        $Descriptors_already_expanded{$alias} = $self->{DESCRIPTORS_EXPANDED}
            = join " ", _expand_descriptors($self->{D_TABLE}, @unexpanded);
    }
    my @desc = split /\s/, $self->{DESCRIPTORS_EXPANDED};

    my $nsubsets = $self->{NUM_SUBSETS};
    my $B_table = $self->{B_TABLE};
    my $maxlen = 1024;
    my $bitstream = chr(255) x $maxlen; # one bits only
    my $pos = 0;
    my @operators;

    my $desc_ref = $desc_refs->[1];

    # All subsets should have same set of expanded descriptors. This
    # is checked later, but we also need to check that the number of
    # descriptors in each subset is the same for all subsets
    my $num_desc = @{$desc_ref};
    foreach my $isub (2..$nsubsets) {
        my $num_d = @{$desc_refs->[$isub]};
        _croak "Compression impossible: Subset 1 contains $num_desc descriptors,"
            . " while subset $isub contains $num_d descriptors"
                if $num_d != $num_desc;
    }


  D_LOOP: for (my $idesc = 0; $idesc < @desc; $idesc++) {
        my $id = $desc[$idesc];
        my $f = substr($id,0,1);
        my $x = substr($id,1,2)+0;
        my $y = substr($id,3,3)+0;

        if ($f == 1) {
            # Delayed replication
            if ($x == 0) {
                _complain("Nonsensical replication of zero descriptors ($id)");
                $idesc++;
                next D_LOOP;
            }
            _croak "$id _expand_descriptors() did not do its job"
                if $y > 0;

            my $next_id = $desc[$idesc+1];
            _croak "$id Erroneous replication factor"
                unless $next_id =~ /^0310(00|01|02|11|12)/ && exists $B_table->{$next_id};
            _croak "Descriptor no $idesc is $desc_ref->[$idesc], expected $next_id"
                if $desc_ref->[$idesc] != $next_id;
            my $factor = $data_refs->[1][$idesc];
            my ($name,$unit,$scale,$refval,$width) = split /\0/, $B_table->{$next_id};
            if ($Spew) {
                $self->_spew(3, "%6s  %-20s  %s", $next_id, $unit, $name);
                $self->_spew(3, "  %s", $factor);
            }
            ($bitstream, $pos, $maxlen)
                = $self->_encode_compressed_value($bitstream,$pos,$maxlen,
                                                  $unit,$scale,$refval,$width,
                                                  $next_id,$data_refs,$idesc,$nsubsets);
            # Include the delayed replication/repetition in descriptor list
            splice @desc, $idesc++, 0, $next_id;

            my @r = ();
            push @r, @desc[($idesc+2)..($idesc+$x+1)] while $factor--;
            splice @desc, $idesc, 2+$x, @r;

            if ($next_id eq '031011' || $next_id eq '031012') {
                # For delayed repetition we should include data just
                # once, so skip to the last set in data array
                $idesc += $x * ($data_refs->[1][$idesc-1] - 1);
                # We ought to check that the data sets we skipped are
                # indeed equal to the last set!
                $self->_spew(4, "Delayed repetition ($id $next_id -> @r)") if $Spew;
            } else {
                $self->_spew(4, "Delayed replication ($id $next_id -> @r)") if $Spew;
            }
            if ($idesc < @desc) {
                redo D_LOOP;
            } else {
                last D_LOOP; # Might happen if delayed factor is 0
            }

        } elsif ($f == 2) {
            my $flow;
            my $bm_idesc;
            ($pos, $flow, $bm_idesc, @operators)
                = $self->_apply_operator_descriptor($id, $x, $y, $pos, 0,
                                                    $desc[$idesc+1], @operators);
            if ($flow eq 'redo_bitmap') {
                # Data value is associated with the descriptor
                # defined by bit map. Remember original and new
                # index in descriptor array for the bit mapped
                # values ('dr' = data reference)
                my $dr_idesc;
                if (!defined $bm_idesc) {
                    $dr_idesc = shift @{ $self->{REUSE_BITMAP}->[0] };
                } elsif (!$Show_all_operators) {
                    $dr_idesc = $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                        + $bm_idesc;
                } else {
                    $dr_idesc = $self->{BITMAP_START}[$self->{NUM_BITMAPS}];
                    # Skip operator descriptors
                    while ($bm_idesc-- > 0) {
                        $dr_idesc++;
                        $dr_idesc++ while ($desc[$dr_idesc] >= 200000);
                    }
                }
                push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[0] },
                     $dr_idesc, $idesc;
                $desc[$idesc] = $desc[$dr_idesc];
                redo D_LOOP;
            } elsif ($flow eq 'signify_character') {
                _croak "Descriptor no $idesc is $desc_ref->[$idesc], expected $id"
                    if $desc_ref->[$idesc] != $id;
                # Get ASCII string
                my @values = map { $data_refs->[$_][$idesc] } 1..$nsubsets;
                my $name = 'SIGNIFY CHARACTER';
                my $unit = 'CCITTIA5';
                my ($scale, $refval, $width) = (0, 0, 8*$y);
                ($bitstream, $pos, $maxlen)
                    = $self->_encode_compressed_value($bitstream,$pos,$maxlen,
                                                      $unit,$scale,$refval,$width,
                                                      "205$y",$data_refs,$idesc,$nsubsets);
                next D_LOOP;
            } elsif ($flow eq 'no_value') {
                next D_LOOP;
            }

            # Remove operator descriptor from @desc
            splice @desc, $idesc--, 1;

            next D_LOOP if $flow eq 'next';
            last D_LOOP if $flow eq 'last';
        }

        if ($self->{CHANGE_REFERENCE_VALUE}) {
            # The data descriptor is to be associated with a new
            # reference value, which is fetched from data stream,
            # possibly with f=9 instead of f=0 for descriptor
            $id -= 900000 if $id =~ /^9/;
            _croak "Change reference operator 203Y is not followed by element"
                . " descriptor, but $id" if $f > 0;
            my @new_ref_values = map { $data_refs->[$_][$idesc] } 1..$nsubsets;
            my $new_refval = $new_ref_values[0];
            # Check that they are all the same
            foreach my $val (@new_ref_values[1..$#new_ref_values]) {
                _croak "Change reference value differ between subsets"
                    . " which cannot be combined with BUFR compression"
                        if $val != $new_refval;
            }
            $self->{NEW_REFVAL_OF}{$id} = $new_refval;
            ($bitstream, $pos, $maxlen)
                = $self->_encode_compressed_reference_value($new_refval,$id,$nsubsets,$bitstream,$pos,$maxlen);
            next D_LOOP;
        }

        # If operator 204$y 'Add associated field' is in effect,
        # each data value is preceded by $y bits which should be
        # encoded separately. We choose to provide a descriptor
        # 999999 in this case (like the ECMWF BUFRDC software)
        if ($self->{ADD_ASSOCIATED_FIELD} and $id ne '031021') {
            # First encode associated field
            _croak "Descriptor no $idesc is $desc_ref->[$idesc], expected 999999"
                if $desc_ref->[$idesc] != 999999;
            my @values = map { $data_refs->[$_][$idesc] } 1..$nsubsets;
            my $name = 'ASSOCIATED FIELD';
            my $unit = 'NUMERIC';
            my ($scale, $refval) = (0, 0);
            my $width = $self->{ADD_ASSOCIATED_FIELD};
            if ($Spew) {
                $self->_spew(3, "%6s  %-20s  %s", $id, $unit, $name);
                $self->_spew(3, "  %s", 999999);
            }
            ($bitstream, $pos, $maxlen)
                = $self->_encode_compressed_value($bitstream,$pos,$maxlen,
                                                  $unit,$scale,$refval,$width,
                                                  999999,$data_refs,$idesc,$nsubsets);
            # Insert the artificial 999999 descriptor for the
            # associated value and increment $idesc to prepare for
            # handling the 'real' value below
            splice @desc, $idesc++, 0, 999999;
        }



        # For quality information, if this relates to a bit map we
        # need to store index of the data ($data_idesc) for which
        # the quality information applies, as well as the new
        # index ($idesc) in the descriptor array for the bit
        # mapped values
        if (substr($id,0,3) eq '033'
            && defined $self->{BITMAP_OPERATORS}
            && $self->{BITMAP_OPERATORS}->[-1] eq '222000') {
            if (defined $self->{REUSE_BITMAP}) {
                my $data_idesc = shift @{ $self->{REUSE_BITMAP}->[0] };
                _croak "$id: Not enough quality values provided"
                    if not defined $data_idesc;
                push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[0] },
                     $data_idesc, $idesc;
            } else {
                my $data_idesc = shift @{ $self->{CURRENT_BITMAP} };
                _croak "$id: Not enough quality values provided"
                    if not defined $data_idesc;
                push @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}]->[0] },
                     $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                         + $data_idesc, $idesc;
            }
        }

        if ($id eq '031031' and $self->{BUILD_BITMAP}) {
            # Store the index of expanded descriptors if data is
            # marked as present in data present indicator: 0 is
            # 'present', 1 (undef value) is 'not present'. E.g.
            # bitmap = 1100110 => (2,3,6) is stored in $self->{CURRENT_BITMAP}

            # NB: bit map might vary betwen subsets!!!!????
            if ($data_refs->[1][$idesc] == 0) {
                push @{$self->{CURRENT_BITMAP}}, $self->{BITMAP_INDEX};
            }
            $self->{BITMAP_INDEX}++;
            if ($self->{BACKWARD_DATA_REFERENCE} == $self->{NUM_BITMAPS}) {
                my $numb = $self->{NUM_BITMAPS};
                if (!defined $self->{BITMAP_START}[$numb]) {
                    # Look up the element descriptor immediately
                    # preceding the bitmap operator
                    my $i = $idesc;
                    $i-- while ($desc[$i] ne $self->{BITMAP_OPERATORS}->[-1]
                                && $i >=0);
                    $i-- while ($desc[$i] > 100000 && $i >=0);
                    _croak "No element descriptor preceding bitmap" if $i < 0;
                    $self->{BITMAP_START}[$numb] = $i;
                } else {
                    $self->{BITMAP_START}[$numb]--;
                    _croak "Bitmap too big"
                        if $self->{BITMAP_START}[$numb] < 0;
                }
            }
        } elsif ($self->{BUILD_BITMAP} and $self->{BITMAP_INDEX} > 0) {
            # We have finished building the bit map
            $self->{BUILD_BITMAP} = 0;
            $self->{BITMAP_INDEX} = 0;
            if ($self->{BACKWARD_DATA_REFERENCE} != $self->{NUM_BITMAPS}) {
                $self->{BITMAP_START}[$self->{NUM_BITMAPS}]
                    = $self->{BITMAP_START}[$self->{BACKWARD_DATA_REFERENCE}];
            }
        }

        # We now have a "real" data descriptor
        _croak "Descriptor no $idesc is $desc_ref->[$idesc], expected $id"
            if $desc_ref->[$idesc] != $id;

        # Find the relevant entry in BUFR table B
        _croak "Data descriptor $id is not present in BUFR table B"
            unless exists $B_table->{$id};
        my ($name,$unit,$scale,$refval,$width) = split /\0/, $B_table->{$id};
        if ($Spew) {
            $self->_spew(3, "%6s  %-20s  %s", $id, $unit, $name);
            $self->_spew(3, "  %s", join ' ',
                         map { defined($data_refs->[$_][$idesc]) ?
                                   $data_refs->[$_][$idesc] : 'missing'} 1..$nsubsets );
        }
        ($bitstream, $pos, $maxlen)
            = $self->_encode_compressed_value($bitstream,$pos,$maxlen,
                                              $unit,$scale,$refval,$width,
                                              $id,$data_refs,$idesc,$nsubsets);
    } # End D_LOOP

    # Pad with 0 bits if necessary to get an even or integer number of
    # octets, depending on bufr edition
    my $padnum = $self->{BUFR_EDITION} < 4 ? (16-($pos%16)) % 16 : (8-($pos%8)) % 8;
    if ($padnum > 0) {
        null2bitstream($bitstream, $pos, $padnum);
    }
    my $len = ($pos + $padnum)/8;
    $bitstream = substr $bitstream, 0, $len;

    return ($bitstream, $len);
}

## Check that the length of data section computed from expansion of
## section 3 ($comp_len) equals actual length of data part of section
## 4, allowing for padding zero bits according to BUFR Regulation 94.1.3
## Strict checking should also check that padding actually consists of
## zero bits only.
sub _check_section4_length {
    my $self = shift;
    my ($comp_len, $actual_len) = @_;

    if ($comp_len > $actual_len) {
        _croak "More descriptors in expansion of section 3"
            . " than what can fit in the given length of section 4"
                . " ($comp_len versus $actual_len bits)";
    } else {
        return if not $Strict_checking; # Excessive bytes in section 4
                                        # does not prevent further decoding
        return if $Noqc;  # No more sensible checks to do in this case

        my $bufr_edition = $self->{BUFR_EDITION};
        my $actual_bytes = $actual_len/8; # This is sure to be an integer
        if ($bufr_edition < 4 and $actual_bytes % 2) {
            _complain("Section 4 is odd number ($actual_bytes) of bytes,"
                      . " which is an error in BUFR edition $bufr_edition");
        }
        my $comp_bytes = int($comp_len/8);
        $comp_bytes++ if $comp_len % 8; # Need to pad with zero bits
        $comp_bytes++ if $bufr_edition < 4 and $comp_bytes % 2; # Need to pad with an extra byte of zero bits
        if ($actual_bytes > $comp_bytes) {
            _complain("Binary data part of section 4 longer ($actual_bytes bytes)"
                      . " than expected from section 3 ($comp_bytes bytes)");
        }
    }
    return;
}

# Trim string, also removing nulls (and _complain if nulls found).
# If strict_checking, checks also for bit 1 set in each character
sub _trim {
    my ($str, $id) = @_;
    return unless defined $str;
    if ($str =~ /\0/) {
        (my $str2 = $str) =~ s|\0|\\0|g;
        _complain("Nulls (" . '\0'
                  . ") found in string '$str2' for descriptor $id");
        $str =~ s/\0//g;
    } elsif ($Strict_checking && $str =~/^ +$/) {
        _complain("Only spaces ('$str') found for descriptor $id, "
                  . "ought to have been encoded as missing value ");
    }

    $str =~ s/\s+$//;
    $str =~ s/^\s+//;

    if ($Strict_checking && $str ne '') {
        foreach my $char (split //, $str) {
            if (ord($char) > 127) {
                _complain("Character $char (ascii value " . ord($char) .
                          ") in string '$str' is not allowed in CCITTIA5");
                last; # Don't want to warn for every bad character
            }
        }
    }
    return $str;
}

## Remove leading and trailing spaces in the strings provided, then add
## spaces if necessary so that all strings have same length as largest
## trimmed string. This length (in bytes) is returned
sub _trimpad {
    my $string_ref = shift;
    my $largest_length = 0;
    foreach my $string (@{$string_ref}) {
        if (defined $string) {
            $string =~ s/^\s+//;
            $string =~ s/\s+$//;
            if (length $string > $largest_length) {
                $largest_length = length $string;
            }
        }
    }
    foreach my $string (@{$string_ref}) {
        if (defined $string) {
            $string .= ' ' x ($largest_length - length $string);
        }
    }
    return $largest_length;
}

## Use timegm in Time::Local to validate date and time in section 1
sub _validate_datetime {
    my $self = shift;
    my $bufr_edition = $self->{BUFR_EDITION};
    my $year = $bufr_edition < 4 ? $self->{YEAR_OF_CENTURY} + 2000
                                 : $self->{YEAR};
    my $month = $self->{MONTH} - 1;
    my $second = $bufr_edition == 4 ? $self->{SECOND} : 0;

    # All datetime variables set to 0 should be considered ok
    return if ($self->{MINUTE} == 0 && $self->{HOUR} == 0
           && $self->{DAY} == 0 && $self->{MONTH} == 0
           && $second == 0 && ($year == 0 || $year == 2000));

    eval {
        my $dummy = timegm($second,$self->{MINUTE},$self->{HOUR},
                           $self->{DAY},$month,$year);
    };

    _complain("Invalid date in section 1: $@") if $@;
}

## Return number of bits necessary to store the nonnegative number $n
## (1 for 0,1, 2 for 2,3, 3 for 4,5,6,7 etc)
sub _get_number_of_bits_to_store {
    my $n = shift;
    return 1 if $n == 0;
    my $x = 1;
    my $i = 0;
    while ($x < $n) {
        $i++;
        $x *= 2;
    }
    return $x==$n ? $i+1 : $i;
}

## Find minimum value among set of numbers (undefined values
## permitted, but at least one value must be defined). Also returns
## for which number the minimum occurs (counting from 1).
sub _minimum {
    my $v_ref = shift;
    my $min = 2**63;
    my $idx = 0;
    my $i=0;
    foreach my $v (@{$v_ref}) {
        $i++;
        next if not defined $v;
        if ($v < $min) {
            $min = $v;
            $idx = $i;
        }
    }
    return ($min, $idx);
}

## Find maximum value among set of nonnegative numbers or undefined values
sub _maximum {
    my $v_ref = shift;
    my $max = 0;
    foreach my $v (@{$v_ref}) {
        next if not defined $v;
        if ($v > $max) {
            $max = $v;
        }
    }
    _croak "Internal error: Found no maximum value" if $max < 0;
    return $max;
}

## Return index of first occurrence av $value in $list, undef if no match
sub _get_index_in_list {
    my ($list, $value) = @_;
    for (my $i=0; $i <= $#{$list}; $i++) {
        if ($list->[$i] eq $value) { # Match
            return $i;
        }
    }
    # No match
    return undef;
}

## Apply the operator descriptor $id, adjusting $pos and
## @operators. Also returning $bm_idesc (explained in start of module)
## and a hint of what to do next in $flow
sub _apply_operator_descriptor {
    my $self = shift;
    my ($id, $x, $y, $pos, $isub, $next_id, @operators) = @_;
    # $isub should be 0 for compressed messages, else subset number

    my $flow = '';
    my $bm_idesc = '';

    if ($y == 0 && $x =~ /^[12378]$/) {
        # 20[12378]000 Cancellation of a data descriptor operator
        _complain("$id Cancelling unused operator")
            if $Strict_checking and !grep {$_ == $x} @operators;
        @operators = grep {$_ != $x} @operators;
        if ($x == 1) {
            $self->{NUM_CHANGE_OPERATORS}-- if $self->{CHANGE_WIDTH};
            undef $self->{CHANGE_WIDTH};
        } elsif ($x == 2) {
            $self->{NUM_CHANGE_OPERATORS}-- if $self->{CHANGE_SCALE};
            undef $self->{CHANGE_SCALE};
        } elsif ($x == 3) {
            $self->{NUM_CHANGE_OPERATORS}-- if $self->{NEW_REFVAL_OF};
            undef $self->{NEW_REFVAL_OF};
        } elsif ($x == 7) {
            $self->{NUM_CHANGE_OPERATORS}-- if $self->{CHANGE_SRW};
            undef $self->{CHANGE_SRW};
        } elsif ($x == 8) {
            $self->{NUM_CHANGE_OPERATORS}-- if $self->{CHANGE_CCITTIA5_WIDTH};
            undef $self->{CHANGE_CCITTIA5_WIDTH};
        }
        $self->_spew(4, "$id * Reset %s",
                     ("width of CCITTIA5 field","data width","scale","reference values",0,0,0,
                     "increase of scale, reference value and data width")[$x % 8]) if $Spew;
        $flow = 'next';
    } elsif ($x == 1) {
        # ^201 Change data width
        _croak "201 operator cannot be nested within 207 operator"
            if grep {$_ == 7} @operators;
        $self->{NUM_CHANGE_OPERATORS}++ if !$self->{CHANGE_WIDTH};
        $self->{CHANGE_WIDTH} = $y-128;
        $self->_spew(4, "$id * Change data width: %d", $self->{CHANGE_WIDTH}) if $Spew;
        push @operators, $x;
        $flow = 'next';
    } elsif ($x == 2) {
        # ^202 Change scale
        _croak "202 operator cannot be nested within 207 operator"
            if grep {$_ == 7} @operators;
        $self->{NUM_CHANGE_OPERATORS}++ if !$self->{CHANGE_SCALE};
        $self->{CHANGE_SCALE} = $y-128;
        $self->_spew(4, "$id * Change scale: %d", $self->{CHANGE_SCALE}) if $Spew;
        push @operators, $x;
        $flow = 'next';
    } elsif ($x == 3 && $y == 255) {
        # 203255 Terminate change reference value definition
        $self->_spew(4, "$id * Terminate reference value definition %s",
                     '203' . (defined $self->{CHANGE_REFERENCE_VALUE}
                     ? sprintf("%03d", $self->{CHANGE_REFERENCE_VALUE}) : '???')) if $Spew;
        _complain("$id no current change reference value to terminate")
            unless defined $self->{CHANGE_REFERENCE_VALUE};
        undef $self->{CHANGE_REFERENCE_VALUE};
        $flow = 'next';
    } elsif ($x == 3) {
        # ^203 Change reference value
        _croak "203 operator cannot be nested within 207 operator"
            if grep {$_ == 7} @operators;
        $self->_spew(4, "$id * Change reference value") if $Spew;
        # Get reference value from data stream ($y == number of bits)
        $self->{NUM_CHANGE_OPERATORS}++ if !$self->{CHANGE_REFERENCE_VALUE};
        $self->{CHANGE_REFERENCE_VALUE} = $y;
        push @operators, $x;
        $flow = 'next';
    } elsif ($x == 4) {
        # ^204 Add associated field
        if ($y > 0) {
            _croak "$id Nesting of Add associated field is not implemented"
                if $self->{ADD_ASSOCIATED_FIELD};
            $self->{ADD_ASSOCIATED_FIELD} = $y;
            $flow = 'next';
        } else {
            _complain "$id No previous Add associated field"
                unless defined $self->{ADD_ASSOCIATED_FIELD};
            undef $self->{ADD_ASSOCIATED_FIELD};
            $flow = 'next';
        }
    } elsif ($x == 5) {
        # ^205 Signify character (i.e. the following $y bytes is
        # character information)
        $flow = 'signify_character';
    } elsif ($x == 6) {
        # ^206 Signify data width for the immediately following local
        # descriptor. If we find this local descriptor in BUFR table B
        # with data width $y bits, we assume we can use this table
        # entry to decode/encode the value properly, and can just
        # ignore the operator descriptor. Else we skip the local
        # descriptor and the corresponding value if decoding, or have
        # to give up if encoding
        my $ff = substr($next_id,0,1);
        _croak("Descriptor $next_id following Signify data width"
                  . "  operator $_ is not an element descriptor")
            if $ff != 0;
        if ($Strict_checking) {
            my $xx = substr($next_id,1,2);
            my $yy = substr($next_id,3,3);
            _complain("Descriptor $next_id following Signify data width"
                  . "  operator $id is not a local descriptor")
                if ($xx < 48 && $yy < 192);
        }
        if (exists $self->{B_TABLE}->{$next_id}
            and (split /\0/, $self->{B_TABLE}->{$next_id})[-1] == $y) {
            $self->_spew(4, "Found $next_id with data width $y, ignoring $id") if $Spew;
            $flow = 'next';
        } else {
            _croak "Cannot encode descriptor $next_id (following $id), not found in table B"
                if $self->{CODING} eq 'ENCODE';
            $self->_spew(4, "$_: Did not find $next_id in table B."
                         . " Skipping $id and $next_id.") if $Spew;
            $pos += $y;  # Skip next $y bits in bitstream if decoding
            $flow = 'skip';
        }

    } elsif ($x == 7) {
        # ^207 Increase scale, reference value and data width
        _croak "207 operator cannot be nested within 201/202/203 operators"
            if grep {$_ == 1 || $_ == 2 || $_ == 3} @operators;
        $self->{NUM_CHANGE_OPERATORS}++ if !$self->{CHANGE_SRW};
        $self->{CHANGE_SRW} = $y;
        $self->_spew(4, "$id * Increase scale, reference value and data width: %d", $y) if $Spew;
        push @operators, $x;
        $flow = 'next';
    } elsif ($x == 8) {
        # ^208 Change data width for ascii data
        $self->{NUM_CHANGE_OPERATORS}++ if !$self->{CHANGE_CCITTIA5_WIDTH};
        $self->{CHANGE_CCITTIA5_WIDTH} = $y*8;
        $self->_spew(4, "$id * Change width for CCITTIA5 field: %d bytes", $y) if $Spew;
        push @operators, $x;
        $flow = 'next';
    } elsif ($x == 9) {
        # ^209 IEEE floating point representation
        _croak "$id IEEE floating point representation (not implemented)";
    } elsif ($x == 21) {
        # ^221 Data not present
        _croak "$id Data not present (not implemented)";
    } elsif ($x == 22 && $y == 0) {
        # 222000 Quality information follows
        push @{ $self->{BITMAP_OPERATORS} }, '222000';
        $self->{NUM_BITMAPS}++;
        # Mark that a bit map probably needs to be built
        $self->{BUILD_BITMAP} = 1;
        $self->{BITMAP_INDEX} = 0;
        $flow = $Noqc ? 'last' : 'no_value';
    } elsif ($x == 23 && $y == 0) {
        # 223000 Substituted values follow, each one following a
        # descriptor 223255. Which value they are a substitute for is
        # defined by a bit map, which already may have been defined
        # (if descriptor 23700 is encountered), or will shortly be
        # defined by data present indicators (031031)
        push @{ $self->{BITMAP_OPERATORS} }, '223000';
        $self->{NUM_BITMAPS}++;
        # Mark that a bit map probably needs to be built
        $self->{BUILD_BITMAP} = 1;
        $self->{BITMAP_INDEX} = 0;
        $flow = 'no_value';
    } elsif ($x == 23 && $y == 255) {
        # 223255 Substituted values marker operator
        _croak "$id No bit map defined"
            unless (defined $self->{CURRENT_BITMAP} || defined $self->{REUSE_BITMAP})
            && $self->{BITMAP_OPERATORS}[-1] eq '223000';
        if (defined $self->{REUSE_BITMAP}) {
            _croak "More 223255 encountered than current bit map allows"
                unless @{ $self->{REUSE_BITMAP}->[$isub] };
            $bm_idesc = undef;
        } else {
            _croak "More 223255 encountered than current bit map allows"
                unless @{$self->{CURRENT_BITMAP}};
            $bm_idesc = shift @{$self->{CURRENT_BITMAP}};
        }
        $flow = 'redo_bitmap';
    } elsif ($x == 24 && $y == 0) {
        # 224000 First order statistical values follow
        push @{ $self->{BITMAP_OPERATORS} }, '224000';
        $self->{NUM_BITMAPS}++;
        # Mark that a bit map probably needs to be built
        $self->{BUILD_BITMAP} = 1;
        $self->{BITMAP_INDEX} = 0;
        $flow = 'no_value';
    } elsif ($x == 24 && $y == 255) {
        # 224255 First order statistical values marker operator
        _croak "$id No bit map defined"
            unless (defined $self->{CURRENT_BITMAP} || defined $self->{REUSE_BITMAP})
            && $self->{BITMAP_OPERATORS}[-1] eq '224000';
        if (defined $self->{REUSE_BITMAP}) {
            _croak "More 224255 encountered than current bit map allows"
                unless @{ $self->{REUSE_BITMAP}->[$isub] };
            $bm_idesc = undef;
        } else {
            _croak "More 224255 encountered than current bit map allows"
                unless @{$self->{CURRENT_BITMAP}};
            $bm_idesc = shift @{$self->{CURRENT_BITMAP}};
        }
        $flow = 'redo_bitmap';
    } elsif ($x == 25 && $y == 0) {
        # 225000 Difference statistical values follow
        push @{ $self->{BITMAP_OPERATORS} }, '225000';
        $self->{NUM_BITMAPS}++;
        # Mark that a bit map probably needs to be built
        $self->{BUILD_BITMAP} = 1;
        $self->{BITMAP_INDEX} = 0;
        $flow = 'no_value';
    } elsif ($x == 25 && $y == 255) {
        # 225255 Difference statistical values marker operator
        _croak "$id No bit map defined\n"
            unless (defined $self->{CURRENT_BITMAP} || defined $self->{REUSE_BITMAP})
            && $self->{BITMAP_OPERATORS}[-1] eq '225000';
        if (defined $self->{REUSE_BITMAP}) {
            _croak "More 225255 encountered than current bit map allows"
                unless @{ $self->{REUSE_BITMAP}->[$isub] };
            $bm_idesc = undef;
        } else {
            _croak "More 225255 encountered than current bit map allows"
                unless @{$self->{CURRENT_BITMAP}};
            $bm_idesc = shift @{$self->{CURRENT_BITMAP}};
        }
        # Must remember to change data width and reference value
        $self->{NUM_CHANGE_OPERATORS}++ if !$self->{DIFFERENCE_STATISTICAL_VALUE};
        $self->{DIFFERENCE_STATISTICAL_VALUE} = 1;
        $flow = 'redo_bitmap';
    } elsif ($x == 32 && $y == 0) {
        # 232000 Replaced/retained values follow, each one following a
        # descriptor 232255. Which value they are a replacement for is
        # defined by a bit map, which already may have been defined
        # (if descriptor 23700 is encountered), or will shortly be
        # defined by data present indicators (031031)
        push @{ $self->{BITMAP_OPERATORS} }, '232000';
        $self->{NUM_BITMAPS}++;
        # Mark that a bit map probably needs to be built
        $self->{BUILD_BITMAP} = 1;
        $self->{BITMAP_INDEX} = 0;
        $flow = 'no_value';
    } elsif ($x == 32 && $y == 255) {
        # 232255 Replaced/retained values marker operator
        _croak "$id No bit map defined"
            unless (defined $self->{CURRENT_BITMAP} || defined $self->{REUSE_BITMAP})
            && $self->{BITMAP_OPERATORS}[-1] eq '232000';
        if (defined $self->{REUSE_BITMAP}) {
            _croak "More 232255 encountered than current bit map allows"
                unless @{ $self->{REUSE_BITMAP}->[$isub] };
            $bm_idesc = undef;
        } else {
            _croak "More 232255 encountered than current bit map allows"
                unless @{$self->{CURRENT_BITMAP}};
            $bm_idesc = shift @{$self->{CURRENT_BITMAP}};
        }
        $flow = 'redo_bitmap';
    } elsif ($x == 35 && $y == 0) {
        # 235000 Cancel backward data reference
        undef $self->{REUSE_BITMAP};
        $self->{BACKWARD_DATA_REFERENCE} = $self->{NUM_BITMAPS} + 1;
        $flow = 'no_value';
    } elsif ($x == 36 && $y == 0) {
        # 236000 Define data present bit map
        undef $self->{CURRENT_BITMAP};
        $self->{BUILD_BITMAP} = 1;
        $self->{BITMAP_INDEX} = 0;
        $flow = 'no_value';
    } elsif ($x == 37 && $y == 0) {
        # 237000 Use defined data present bit map
        _croak "$id No previous bit map defined"
            unless defined $self->{BITMAPS};
        my %hash = @{ $self->{BITMAPS}->[$self->{NUM_BITMAPS}-1]->[$isub] };
        $self->{REUSE_BITMAP}->[$isub] = [sort {$a <=> $b} keys %hash];
        $flow = 'no_value';
    } elsif ($x == 37 && $y == 255) {
        # 237255 Cancel 'use defined data present bit map'
        _complain("$id No data present bit map to cancel")
            unless defined $self->{REUSE_BITMAP};
        undef $self->{REUSE_BITMAP};
        $flow = 'next';
    } elsif ($x == 41 && $y == 0) {
        # 241000 Define event
        _croak "$id Define event (not implemented)";
    } elsif ($x == 41 && $y == 255) {
        # 241255 Cancel define event
        _croak "$id Cancel define event (not implemented)";
    } elsif ($x == 42 && $y == 0) {
        # 242000 Define conditioning event
        _croak "$id Define conditioning event (not implemented)";
    } elsif ($x == 42 && $y == 255) {
        # 242255 Cancel define conditioning event
        _croak "$id Cancel define conditioning event (not implemented)";
    } elsif ($x == 43 && $y == 0) {
        # 243000 Categorial forecast values follow
        _croak "$id Categorial forecast values follow (not implemented)";
    } elsif ($x == 43 && $y == 255) {
        # 243255 Cancel categorial forecast values follow
        _croak "$id Cancel categorial forecast values follow (not implemented)";
    } else {
        _croak "$id Unknown data description operator";
    }

    return ($pos, $flow, $bm_idesc, @operators);
}

## Extract data from selected subsets in selected bufr objects, joined
## into a single ($data_refs, $desc_refs), to later be able to make a
## single BUFR message by calling encode_message. Also returns number
## of subsets extracted.
sub join_subsets {
    my $self = shift;
    my (@bufr, @subset_list);
    my $last_arg_was_bufr;
    my $num_objects = 0;
    while (@_) {
        my $arg = shift;
        if (ref($arg) eq 'Geo::BUFR') {
            $bufr[$num_objects++] = $arg;
            $last_arg_was_bufr = 1;
        } elsif (ref($arg) eq 'ARRAY') {
            _croak "Wrong input (multiple array refs) to join_subsets"
                unless $last_arg_was_bufr;
            $subset_list[$num_objects-1] = $arg;
            $last_arg_was_bufr = 0;
        } else {
            _croak "Input is not Geo::BUFR object or array ref in join_subsets";
        }
    }

    my ($data_refs, $desc_refs);
    my $n = 1; # Number of subsets included
    # Ought to check for common section 3 also?
    for (my $i=0; $i < $num_objects; $i++) {
        $bufr[$i]->rewind();
        my $isub = 1;
        if (!exists $subset_list[$i]) { # grab all subsets from this object
            while (not $bufr[$i]->eof()) {
                my ($data, $descriptors) = $bufr[$i]->next_observation();
                last if !$data;
                $self->_spew(2, "Joining subset %d from bufr object %d", $isub, $i) if $Spew;
                $data_refs->[$n] = $data;
                $desc_refs->[$n++] = $descriptors;
                $isub++;
            }
        } else { # grab the subsets specified, also inserting them in the specified order
            my $num_found = 0;
            while (not $bufr[$i]->eof()) {
                my ($data, $descriptors) = $bufr[$i]->next_observation();
                last if !$data;
                my $index = _get_index_in_list($subset_list[$i], $isub);
                if (defined $index) {
                    $self->_spew(2, "Joining subset %d from subset %d"
                                 . " in bufr object %d", $isub, $index, $i) if $Spew;
                    $data_refs->[$n + $index] = $data;
                    $desc_refs->[$n + $index] = $descriptors;
                    $num_found++;
                }
                $isub++;
            }
            _croak "Mismatch between number of subsets found ($num_found) and "
                . "expected from argument [@{$subset_list[$i]}] to join_subsets"
                    if $num_found != @{$subset_list[$i]};
            $n += $num_found;
        }
        $bufr[$i]->rewind();
    }
    $n--;
    return ($data_refs, $desc_refs, $n)
}

1;  # Make sure require or use succeeds.


__END__