code: func hash(key uint64) uint64 {
  	key ^= key >> 33
  	key *= 0xff51afd7ed558ccd
  	key ^= key >> 33
  	key *= 0xc4ceb9fe1a85ec53
  	key ^= key >> 33
  	return key
  }
docs: // hash will convert the uint64 key into a hash based on Murmur3's 64-bit
  // integer finalizer.
  // Details here: https://code.google.com/p/smhasher/wiki/MurmurHash3