use go 1.12

Signed-off-by: hongming <talonwan@yunify.com>

vendor/github.com/lucas-clemente/quic-go/internal/protocol/packet_number.go

@@ -0,0 +1,70 @@
+package protocol
+
+// InferPacketNumber calculates the packet number based on the received packet number, its length and the last seen packet number
+func InferPacketNumber(
+	packetNumberLength PacketNumberLen,
+	lastPacketNumber PacketNumber,
+	wirePacketNumber PacketNumber,
+	version VersionNumber,
+) PacketNumber {
+	var epochDelta PacketNumber
+	if version.UsesVarintPacketNumbers() {
+		switch packetNumberLength {
+		case PacketNumberLen1:
+			epochDelta = PacketNumber(1) << 7
+		case PacketNumberLen2:
+			epochDelta = PacketNumber(1) << 14
+		case PacketNumberLen4:
+			epochDelta = PacketNumber(1) << 30
+		}
+	} else {
+		epochDelta = PacketNumber(1) << (uint8(packetNumberLength) * 8)
+	}
+	epoch := lastPacketNumber & ^(epochDelta - 1)
+	prevEpochBegin := epoch - epochDelta
+	nextEpochBegin := epoch + epochDelta
+	return closestTo(
+		lastPacketNumber+1,
+		epoch+wirePacketNumber,
+		closestTo(lastPacketNumber+1, prevEpochBegin+wirePacketNumber, nextEpochBegin+wirePacketNumber),
+	)
+}
+
+func closestTo(target, a, b PacketNumber) PacketNumber {
+	if delta(target, a) < delta(target, b) {
+		return a
+	}
+	return b
+}
+
+func delta(a, b PacketNumber) PacketNumber {
+	if a < b {
+		return b - a
+	}
+	return a - b
+}
+
+// GetPacketNumberLengthForHeader gets the length of the packet number for the public header
+// it never chooses a PacketNumberLen of 1 byte, since this is too short under certain circumstances
+func GetPacketNumberLengthForHeader(packetNumber, leastUnacked PacketNumber, version VersionNumber) PacketNumberLen {
+	diff := uint64(packetNumber - leastUnacked)
+	if version.UsesVarintPacketNumbers() && diff < (1<<(14-1)) ||
+		!version.UsesVarintPacketNumbers() && diff < (1<<(16-1)) {
+		return PacketNumberLen2
+	}
+	return PacketNumberLen4
+}
+
+// GetPacketNumberLength gets the minimum length needed to fully represent the packet number
+func GetPacketNumberLength(packetNumber PacketNumber) PacketNumberLen {
+	if packetNumber < (1 << (uint8(PacketNumberLen1) * 8)) {
+		return PacketNumberLen1
+	}
+	if packetNumber < (1 << (uint8(PacketNumberLen2) * 8)) {
+		return PacketNumberLen2
+	}
+	if packetNumber < (1 << (uint8(PacketNumberLen4) * 8)) {
+		return PacketNumberLen4
+	}
+	return PacketNumberLen6
+}