docs: private static int hash(long x, int length) {
          int h = (int)(x ^ (x >>> 32));
          // This function ensures that hashCodes that differ only by
          // constant multiples at each bit position have a bounded
          // number of collisions (approximately 8 at default load factor).
          h ^= (h >>> 20) ^ (h >>> 12);
          h ^= (h >>> 7) ^ (h >>> 4);
          return (h) & (length - 2);
      }