100 lines/100 iterations:
          Rate bitwise  ifchop
bitwise 33.1/s      --    -41%
ifchop  56.5/s     71%      --

10 lines/10000 iterations:
          Rate bitwise  ifchop
bitwise 3226/s      --    -57%
ifchop  7463/s    131%      --

1000 lines/5 iterations:
        s/iter bitwise  ifchop
bitwise   3.06      --    -23%
ifchop    2.37     29%      --

##</code><code>##

          Rate  ifchop bitwise
ifchop  4.22/s      --    -87%
bitwise 33.3/s    690%      --

##</code><code>##

#!/usr/bin/perl -w
use strict;
use Benchmark qw(cmpthese);

our $S ||= 1;
our $B ||= 32;
our $N ||= 100;

srand( 1 );

our @strings = map {
    unpack 'b'. $B, rand( 2**32 )
} 1 .. $N;

my $bitwise = <<'EOBW';
our @strings;
my ($c00, $c01, $c10, $c11) = (0, 0, 0, 0);
for my $i ( 0 .. $#strings ) {
    for my $j ( $i+1 .. $#strings ) {
            $c00 = (  $strings[ $i ] |  $strings[ $j ] ) =~ tr[0][0];
            $c01 = ( ~$strings[ $i ] &  $strings[ $j ] ) =~ tr[\1][\1];
            $c10 = (  $strings[ $i ] & ~$strings[ $j ] ) =~ tr[\1][\1];
            $c11 = (  $strings[ $i ] &  $strings[ $j ] ) =~ tr[1][1];
    }
}
EOBW

my $ifchop = <<'EOIFC';
our @strings;
my ($c00, $c01, $c10, $c11) = (0, 0, 0, 0); 
for my $i ( 0 .. $#strings ) {
  for my $j ( $i+1 .. $#strings ) {
    # Need copies because chop is destructive
    # Oops... my $test_str_1 = $i;
    # my $test_str_2 = $j;
    my $test_str_1 = $strings[$i];
    my $test_str_2 = $strings[$j];

    while ($test_str_1) {
      my $x = chop $test_str_1;
      my $y = chop $test_str_2;
      if ($x) {
        if ($y) {
          $c11++;
        } else {
          $c10++;
        }
      } else {
        if ($y) {
          $c01++;
        } else {
          $c00++;
        }
      }
    }
  } 
}
EOIFC

cmpthese(100,
         { bitwise => $bitwise,
           ifchop  => $ifchop,
         });