smwrand.py

# smwrand
# Ryan Finnie <ryan@finnie.org>
# Based on deconstruction by Retro Game Mechanics Explained
# https://www.youtube.com/watch?v=q15yNrJHOak

class SMWRand:
    seed_1 = 0
    seed_2 = 0

    def _rand(self):
        self.seed_1 = (self.seed_1 + (self.seed_1 << 2) + 1) & 0xff
        self.seed_2 = ((self.seed_2 << 1) + int((self.seed_2 & 0x90) in (0x90, 0))) & 0xff
        return self.seed_1 ^ self.seed_2

    def rand(self):
        output_2 = self._rand()
        output_1 = self._rand()
        return (output_1, output_2)


if __name__ == '__main__':
    smwrand = SMWRand()
    for i in range(20):
        r = smwrand.rand()
        print('Seed (post-output): 0x{:02x} 0x{:02x}, output: 0x{:02x} 0x{:02x}'.format(
            smwrand.seed_1, smwrand.seed_2, r[0], r[1],
        ))