Fast code and maintainable code are often contrary goals. 
use strict;
my $row = join '', map '0', 1..18;
$row .= "\n";
for my $i_1 (0..12) {
  substr($row, $i_1, 1, 1);
  for my $i_2 (($i_1+1)..13) {
    substr($row, $i_2, 1, 1);
    for my $i_3 (($i_2+1)..14) {
      substr($row, $i_3, 1, 1);
      for my $i_4 (($i_3+1)..15) {
        substr($row, $i_4, 1, 1);
        for my $i_5 (($i_4+1)..16) {
          substr($row, $i_5, 1, 1);
          for my $i_6 (($i_5+1)..17) {
            substr($row, $i_6, 1, 1);
            print $row;
            substr($row, $i_6, 1, 0);
          }
          substr($row,$i_5, 1, 0);
        }
        substr($row, $i_4, 1, 0);
      }
      substr($row, $i_3, 1, 0);
    }
    substr($row, $i_2, 1, 0);
  }
  substr($row, $i_1, 1, 0);
}

[download]
My next try at getting faster would be to go to Inline.

In reply to Re (tilly) 1: Is there a faster way to do this? by tilly
in thread Permutations in binary by Anonymous Monk

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