File Coverage

blib/lib/Algorithm/InversionList.pm

Criterion	Covered	Total	%
statement	36	36	100.0
branch	9	12	75.0
condition	1	3	33.3
subroutine	5	5	100.0
pod	0	2	0.0
total	51	58	87.9

package Algorithm::InversionList;

use 5.006;
use strict;
use warnings;

require Exporter;

our @ISA = qw(Exporter);

our @EXPORT = qw(
invlist data_from_invlist
);
our $VERSION = '0.03';

sub invlist
{
 my $string = shift @_;

 # we need a valid string
 return undef unless defined $string;

 # handle trivial case of 0-length string
 return [] unless length $string;

 # this is suboptimal, we eventually want to do things in multiples of 8 (on byte boundaries)
 # $length is length in bits, we avoid b* because it will create a list 8 times larger than C*
 my @unpacked = unpack("C*", $string);
 my $length = scalar @unpacked * 8;
 my $current = vec($string, 0, 1);
 my $new;
 my @list;

 push @list, 0 if $current;

 foreach my $offset (0..$length)
 {
  $new = vec($string, $offset, 1);
  if ($new != $current)
  {
   push @list, $offset;
  }
  $current = $new;
 }

 push @list, $length unless exists $list[-1] && $list[-1] == $length;

 return \@list;
}

sub data_from_invlist
{
 my $out = '';				# start with a blank string
 my $append = 0;			# we're appending '0' bits first
 my $list = shift @_;

 return undef unless defined $list;

 my $start_offset = 0;
 foreach my $end_offset (@$list)			# for each inversion list value
 {
  foreach my $offset ($start_offset .. $end_offset-1)
  {
   vec($out, $offset, 1) = $append;
  }

  $append++;				# 0 => 1, 1 => 2
  $append %= 2;				# 2 => 0, 1 => 1
  $start_offset = $end_offset;
 }

 return $out;				# return the data
}

1;
__END__