Below is the file 'twiddle.pl' from this revision. You can also download the file.

#!/usr/pkg/bin/perl

binmode STDIN;
binmode STDOUT;

while (1)
{
    my $byte = getc;
    last unless defined($byte);
    $byte = ord($byte);
    $a = $byte & 0x08;
    $b = $byte & 0x10;
    $byte = $byte & 0xe7;
    $byte = $byte | 0x08 if ($b);
    $byte = $byte | 0x10 if ($a);
    printf "%c", $byte;
}