sub using_str_bit_ops_and_s {
   my ($s1, $s2) = @_;
   (my $mask = $s1) =~ tr/\x00/\xFF/c;
   return ($s1 & $mask) | ($s2 & ~$mask);
}

##</code><code>##

sub using_str_bit_xor {
   my ($s1, $s2) = @_;
   (my $mask = $s1) =~ tr/\x00/\xFF/c;
   return (($s1 ^ $s2) & $mask ) ^ $s2;
}

##</code><code>##

my $x = pack 'C*', map int rand(256), 1 .. 64*1024;
my $y = pack 'C*', map int rand(256), 1 .. 64*1024;
using_str_bit_ops_and_s($x, $y) eq using_str_bit_xor($x, $y)
  or die "Results are different??";

use Benchmark 'cmpthese';
cmpthese -3, {
  using_str_bit_ops_and_s => sub{ my $r = using_str_bit_ops_and_s($x, $y) },
  using_str_bit_xor=> sub{ my $r = using_str_bit_xor($x, $y) },
};

##</code><code>##

                         Rate using_str_bit_ops_and_s       using_str_bit_xor
using_str_bit_ops_and_s 686/s                      --                    -16%
using_str_bit_xor       821/s                     20%                      --