File Coverage

blib/lib/Math/NumSeq/MephistoWaltz.pm

Criterion	Covered	Total	%
statement	55	58	94.8
branch	5	6	83.3
condition	0	3	0.0
subroutine	13	14	92.8
pod	4	4	100.0
total	77	85	90.5

# Copyright 2011, 2012, 2013, 2014 Kevin Ryde

# This file is part of Math-NumSeq.
#
# Math-NumSeq is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 3, or (at your option) any later
# version.
#
# Math-NumSeq is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
# for more details.
#
# You should have received a copy of the GNU General Public License along
# with Math-NumSeq.  If not, see .


# Fractal turn sequence:

# "Infinite streams", Jorg Endrullis, Clemens Grabmayer, Dimitri Hendriks,
# Jan Willem Klop, www.phil.uu.nl/~clemens/linkedfiles/NVTI2009.pdf


package Math::NumSeq::MephistoWaltz;
use 5.004;
use strict;

use vars '$VERSION', '@ISA';
$VERSION = 71;
use Math::NumSeq;
@ISA = ('Math::NumSeq');
*_is_infinite = \&Math::NumSeq::_is_infinite;

# uncomment this to run the ### lines
#use Smart::Comments;


# use constant name => Math::NumSeq::__('Mephisto Waltz');
use constant description => Math::NumSeq::__('Mephisto waltz sequence.');
use constant i_start => 0;
use constant values_min => 0;
use constant values_max => 1;
use constant characteristic_integer => 1;

# cf A189658 - positions of 0
#    A189659 - positions of 1
#    A189660 - cumulative 0/1
#    A156595 - xor diffs, OFFSET=0 so a(n) = m(n) xor m(n+1)
#
use constant oeis_anum => 'A064990';  # mephisto waltz 0/1 values

sub rewind {
  my ($self) = @_;
  $self->{'i'} = $self->i_start;
  $self->{'value'} = 1;
  $self->{'low'} = -1;
  $self->{'digits'} = [];
}

my @table = (0,0,1, 0,0,1, 1,1,0,
             0,0,1, 0,0,1, 1,1,0,
             1,1,0, 1,1,0, 0,0,1);
my @delta = (map {$table[$_]^$table[($_+26)%27]} 0 .. $#table);

sub next {
  my ($self) = @_;
  ### MephistoWaltz next(): $self->{'i'}
  ### at: "low=$self->{'low'}  value=$self->{'value'}"

  my $low;
  if (($low = ++$self->{'low'}) >= 27) {
    $low = $self->{'low'} = 0;
    my $i = 0;
    for (;;) {
      my $digit = ++$self->{'digits'}->[$i];
      ### carry to digit: $digit
      if ($digit >= 27) {
        $self->{'digits'}->[$i++] = 0;
        $self->{'value'} ^= 1;  # three 2s have become 0s
      } else {
        $self->{'value'} ^= $delta[$digit];
        last;
      }
    }
  }

  ### apply: "low=$low delta=$delta[$low]"
  return ($self->{'i'}++,
          ($self->{'value'} ^= $delta[$low]));
}

sub ith {
  my ($self, $i) = @_;
  ### ith(): $i

  if (_is_infinite($i)) {
    return $i;
  }
  my $ret = 0;
  while ($i) {
    $ret ^= $table[$i % 27];
    $i = int($i/27);
  }
  return $ret;
}

sub pred {
  my ($self, $value) = @_;
  return ($value == 0 || $value == 1);
}

1;
__END__