#!/usr/bin/env perl

use strict;
use warnings;

use Benchmark qw{cmpthese};

my $x = 1 << 0;                             
my $y = 1 << 1 ^ 1 << 4 ^ 1 << 7 ^ 1 << 15 ^ 1 << 31 ^ 1 << 63;

my @test_results = (
    hd_OP($x, $y),
    hd_Ken($x, $y),
    hd_OP($x, $y, 16),
    hd_Ken($x, $y, 16),
    hd_OP($x, $y, 32),
    hd_Ken($x, $y, 32),
    hd_OP($x, $y, 64),
    hd_Ken($x, $y, 64),
);
print "Test results: @test_results\n";

cmpthese(-1, {
    hd_OP_8 => sub { hd_OP($x, $y) },
    hd_Ken_8 => sub { hd_Ken($x, $y) },
});

cmpthese(-1, {
    hd_OP_16 => sub { hd_OP($x, $y, 16) },
    hd_Ken_16 => sub { hd_Ken($x, $y, 16) },
});

cmpthese(-1, {
    hd_OP_32 => sub { hd_OP($x, $y, 32) },
    hd_Ken_32 => sub { hd_Ken($x, $y, 32) },
});

cmpthese(-1, {
    hd_OP_64 => sub { hd_OP($x, $y, 64) },
    hd_Ken_64 => sub { hd_Ken($x, $y, 64) },
});

sub hd_Ken {
    my ($diff, $bits, $count, $mask) = ($_[0] ^ $_[1], $_[2] || 8, 0);

    $mask = 1 << $_, $diff & $mask && ++$count for 0 .. $bits - 1;

    $count;
}

sub hd_OP {
   my ($d1,$d2,$bits) = @_;
   $bits ||= 8;
   my $diff = $d1 ^ $d2;
   my $count = 0;
   for my $b ( 0 .. $bits-1 ) {
      my $mask = 1 << $b;
      ++ $count if $diff & $mask
   }
   return $count
}