Comment by wruza

For the curious, xorshift128+:

  uint64_t a = s[0];
  uint64_t b = s[1];

  s[0] = b;
  a ^= a << 23;
  a ^= a >> 18;
  a ^= b;
  a ^= b >>  5;
  s[1] = a;

  return a + b;

https://stackoverflow.com/a/34432126