#! perl -slw use strict; use Time::HiRes qw[ time ]; use Data::Dump qw[ pp ]; our $N ||= 4000; our $S ||= 1; srand( $S ); my @list = map 1 | int( rand( 2**32 )), 1 .. $N; my $start = time; my %hash; for my $i ( 0 .. $#list ) { use integer; my $v = $list[ $i ]; ( $v & $_ ) == 1 and undef $hash{ "$i:$_" } for @list[ $i+1 .. $#list ]; } printf "Took %.3f\n", time() - $start; print 'Odd numbers in list: ', scalar @list; print 'Pairs found: ', scalar keys %hash; #<>; pp \%hash;