code: private static int fmix(int h1, int length) {
      h1 ^= length;
      h1 ^= h1 >>> 16;
      h1 *= 0x85ebca6b;
      h1 ^= h1 >>> 13;
      h1 *= 0xc2b2ae35;
      h1 ^= h1 >>> 16;
      return h1;
    }
docs: Finalization mix - force all bits of a hash block to avalanche