I'm not using % on the result of rand(). I'm using the "Feistal network" construction that is at the heart of the data encryption standard, replacing binary op

I'm not using % on the result of rand(). I'm using the "Feistal network" construction that is at the heart of the data encryption standard, replacing binary operations like 'xor' with the "addition plus modulus" operation. My found function sucks, and I only do 3 rounds, so there's probably some issues there. But, if I were to fix those issues, then there should be no more detectable bias than in the original DES cipher.