sub fletch { my( $str )= @_; my( $sum1, $sum2 ); for my $ch ( unpack "C*", $str ) { $sum1 += $ch; $sum1 -= 255 if 255 < $sum1; $sum2 += $sum1; $sum2 -= 255 if 255 < $sum2; } return pack "C*", $sum2, $sum1; }