code: func lookupTLSHash(hash uint8) (crypto.Hash, error) {
  	switch hash {
  	case hashSHA1:
  		return crypto.SHA1, nil
  	case hashSHA256:
  		return crypto.SHA256, nil
  	case hashSHA384:
  		return crypto.SHA384, nil
  	default:
  		return 0, errors.New("tls: unsupported hash algorithm")
  	}
  }
docs: // lookupTLSHash looks up the corresponding crypto.Hash for a given
  // TLS hash identifier.