2x32-bit xorshift/weyl sequence

gistfile1.txt

// 1 dep-chain (assuming state words in reg) to result.
// DON'T USE ME UNLESS YOUR PARINOID AND
// USING SOMETHING MORE EXPENSIVE (actually inferior
// to some other formulations...period is only 2^32-1)

// Zero is illegal for both state words.
typedef struct { uint32_t s[2]; } rng_state_t;

// smallcrush: passes
// crush: 1 systematic failure = 72  LinearComp, r = 29 

static inline uint32_t rng_u32(rng_state_t* s)
{
  uint32_t x = s->s[1];
  uint32_t r = s->s[0] + x;
  
  s->s[0] = x * 1597334677;
  x ^= (x << 13);
  x ^= (x >> 17);
  x ^= (x << 5);
  s->s[1] = x;

  return r;
}