code: func PubkeyToIDV4(key *ecdsa.PublicKey) ID {
  	e := make([]byte, 64)
  	math.ReadBits(key.X, e[:len(e)/2])
  	math.ReadBits(key.Y, e[len(e)/2:])
  	return ID(crypto.Keccak256Hash(e))
  }
docs: // PubkeyToIDV4 derives the v4 node address from the given public key.