code: func AddUint64(h uint64, u uint64) uint64 {
  	h = (h ^ ((u >> 56) & 0xFF)) * prime64
  	h = (h ^ ((u >> 48) & 0xFF)) * prime64
  	h = (h ^ ((u >> 40) & 0xFF)) * prime64
  	h = (h ^ ((u >> 32) & 0xFF)) * prime64
  	h = (h ^ ((u >> 24) & 0xFF)) * prime64
  	h = (h ^ ((u >> 16) & 0xFF)) * prime64
  	h = (h ^ ((u >> 8) & 0xFF)) * prime64
  	h = (h ^ ((u >> 0) & 0xFF)) * prime64
  	return h
  }
docs: // AddUint64 adds the hash value of the 8 bytes of u to h.