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=cut

our $VERSION = '0.06';


=head1 SYNOPSIS

Use L<Algorithm::Bitonic::Sort> with the following style.

	use Algorithm::Bitonic::Sort;
	
	my @sample = (1,4,8,4,4365,2,67,33,345);
	my @result_inc = bitonic_sort( 1 ,@sample);	# incremental
	my @result_dec = bitonic_sort( 0 ,@sample);	# decremental

=head1 DESCRIPTION

Bitonic mergesort is a parallel algorithm for sorting. It is also used as a construction method for building a sorting network.
This is an Perl 5 implementation of Ken Batcher's Bitonic mergesort.

=head1 Limitation

This is a enhanced version of Bitonic Sort which removed the limitation of original version.
This module supports any amount of numbers.

The original Bitonic can only sort N numbers, which N is a power of 2.


=head1 EXPORT

bitonic_sort


=head1 SUBROUTINES

=head2 bitonic_sort

The First Parameter works as the ascending/decreasing selector.
True (1 or any true value) means ascending (incremental),
False (0 or any false value) means decreasing.

All other params will be treated as members/items to be sorted.


=cut

sub bitonic_sort {
	my $up = shift;
	say '#### Sort: '.Dumper(@_) if DEBUG;
	
	return @_ if int @_ <= 1;
	
	my $single_bit = shift @_ if @_ % 2;
	$single_bit //= 'NA';
	
	say Dumper $single_bit if DEBUG;
	
	my @num = @_;
	my @first = bitonic_sort( 1, @num[0..(@num /2 -1)] );
	my @second = bitonic_sort( 0, @num[(@num /2)..(@num -1)] );
	
	return _bitonic_merge( $up, $single_bit, @first, @second );
}

sub _bitonic_merge {
	my $up = shift;
	say '#### Merge: '.Dumper(@_) if DEBUG;
	
	my $single_bit = shift;
	say Dumper $single_bit if DEBUG;
	
	# assume input @num is bitonic, and sorted list is returned 
	return @_ if int @_ == 1;
	
	my $single_bit_2 = shift @_ if @_ % 2;
	$single_bit_2 //= 'NA';
	
	my @num = @_;
	@num = _bitonic_compare( $up, @num );
	
	my @first = _bitonic_merge( $up, 'NA', @num[0..(@num /2 -1)] );
	my @second = _bitonic_merge( $up, 'NA', @num[(@num /2)..(@num -1)] );
	
	@num = (@first, @second);
	@num = _some_sorting_algorithm( $up, $single_bit, @first, @second ) if $single_bit ne 'NA';
	@num = _some_sorting_algorithm( $up, $single_bit_2, @first, @second ) if $single_bit_2 ne 'NA';
	
	say "#####\n# Merge Result\n#####\n".Dumper(@num)  if DEBUG;
	
	return (@num);
}

sub _bitonic_compare {
	my $up = shift;
	say '#### Compare: '.Dumper(@_) if DEBUG;
	my @num = @_;
	
	my $dist = int @num /2;
	#~ 
	for my $i (0..$dist-1) {
		say "i=$i, dist=$dist, $num[$i] > $num[$i+$dist]) == $up" if DEBUG;
		if ( ($num[$i] > $num[$i+$dist]) == $up ) {
			say "Swapping....." if DEBUG;
			($num[$i], $num[$i+$dist]) = ($num[$i+$dist], $num[$i]);	#swap
		}
	}
	#~ for my $i (0..(int @$first)) {
		#~ if ( ($first->[$i] > $second->[$i]) == $up ) {
			#~ ($first->[$i], $second->[$i]) = ($second->[$i], $first->[$i]);	#swap
		#~ }
	#~ }
	
	say 'Compared result:'.Dumper(@num) if DEBUG;
	return @num;
	#~ return ($first, $second);
}


sub _some_sorting_algorithm {
	my $up = shift;
	my $single_bit = shift;
	my @num = @_;
	my @num_new;
	
	say "_SOME_SORTING_ALGORITHM: INPUT: ".Dumper(@num) if DEBUG;
	
	while (my $curr = shift @num) {
		say "_SOME_SORTING_ALGORITHM: for: ".Dumper($curr, $single_bit, @num) if DEBUG;
		if ($up and $single_bit < $curr) {
			push @num_new, $single_bit;
			push @num_new, $curr;
			say "Return earlier, up is ".($up or '0').':'.Dumper(@num_new, @num) if DEBUG;
			return (@num_new, @num);
		} elsif ($single_bit > $curr and not $up) {
			push @num_new, $single_bit;
			push @num_new, $curr;
			say "Return earlier, up is ".($up or '0').':'.Dumper(@num_new, @num) if DEBUG;
			return (@num_new, @num)
		} else {
			push @num_new, $curr;
		}
	}
	
	push @num_new, $single_bit;
	say "Return normal, ".Dumper(@num_new, @num) if DEBUG;
	return @num_new;
}

=head1 AUTHOR

BlueT - Matthew Lien - 練喆明, C<< <BlueT at BlueT.org> >>


=head1 INSTALLATION

To install this module, run the following commands:

	perl Makefile.PL
	make
	make test
	make install

Or install with cpanm

	cpanm Algorithm::Bitonic::Sort


=head1 BUGS

Please report any bugs or feature requests to CPAN ( C<bug-algorithm-bitonic-sort at rt.cpan.org>, L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Algorithm-Bitonic-Sort> ) or GitHub (L<https://github.com/BlueT/Algorithm-Bitonic-Sort/issues>).
I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.