in reply to Re: Re: Detecting transpositions
in thread Detecting transpositions

Would it be possible for the product of $f ^ $s to contain a "1" and hence pollute your $_ string?

Yes, but no. It could certainly be possible that the XORred string contains a character "1". But this is ok, the tr/\x00/1/c turns anything that is not "\x00" into a "1" anyway - after the tr, the string will only contain "\x00" and "1" characters.