This said, I find the final computation quite elegant and istructive - I wouldn't have thought of XORing letters even in 100 years.

BrowserUk is The XOR Meister.

I had the same reaction as yours when I first encountered the "infamous xor trick" (in this case to find the first position at which two strings differ, or equivalently, the length of the longest common prefix):

$a = "foobar";
$b = "foobAr";
($a ^ $b) =~ /^(\0*)/ and print length $1;
__END__
4
[download]

Way cool, though it works as written only if the characters are 1 byte long.

There's always to learn, luckly, provided I'll be able to remember it when I'll need :)

Yep, that's the rub.