code: func (b UDP) CalculateChecksum(partialChecksum uint16) uint16 {
  	// Calculate the rest of the checksum.
  	return Checksum(b[:UDPMinimumSize], partialChecksum)
  }
docs: // CalculateChecksum calculates the checksum of the udp packet, given the
  // checksum of the network-layer pseudo-header and the checksum of the payload.