You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: packet_number.go
    path of file: ./repos/scan4all/vendor/github.com/quic-go/quic-go/internal/protocol
    
    the code of the file until where you have to start completion: package protocol

// A PacketNumber in QUIC
type PacketNumber int64

// InvalidPacketNumber is 
    
func GetPacketNumberLengthForHeader(packetNumber, leastUnacked PacketNumber) PacketNumberLen {
	diff := uint64(packetNumber - leastUnacked)
	if diff < (1 << (16 - 1)) {
		return PacketNumberLen2
	}
	if diff < (1 << (24 - 1)) {
		return PacketNumberLen3
	}
	return PacketNumberLen4
}