Add tailscale checksum

internal/gtcpip/checksum/checksum.go

@@ -30,34 +30,6 @@ func Put(b []byte, xsum uint16) {
 	binary.BigEndian.PutUint16(b, xsum)
 }
 
-// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
-// given byte array. This function uses an optimized version of the checksum
-// algorithm.
-//
-// The initial checksum must have been computed on an even number of bytes.
-func Checksum(buf []byte, initial uint16) uint16 {
-	s, _ := calculateChecksum(buf, false, initial)
-	return s
-}
-
-// Checksumer calculates checksum defined in RFC 1071.
-type Checksumer struct {
-	sum uint16
-	odd bool
-}
-
-// Add adds b to checksum.
-func (c *Checksumer) Add(b []byte) {
-	if len(b) > 0 {
-		c.sum, c.odd = calculateChecksum(b, c.odd, c.sum)
-	}
-}
-
-// Checksum returns the latest checksum value.
-func (c *Checksumer) Checksum() uint16 {
-	return c.sum
-}
-
 // Combine combines the two uint16 to form their checksum. This is done
 // by adding them and the carry.
 //

internal/gtcpip/checksum/checksum_default.go

@@ -0,0 +1,13 @@
+//go:build !amd64
+
+package checksum
+
+// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
+// given byte array. This function uses an optimized version of the checksum
+// algorithm.
+//
+// The initial checksum must have been computed on an even number of bytes.
+func Checksum(buf []byte, initial uint16) uint16 {
+	s, _ := calculateChecksum(buf, false, initial)
+	return s
+}

internal/gtcpip/checksum/checksum_ts.go

@@ -0,0 +1,9 @@
+//go:build amd64
+
+package checksum
+
+import "github.com/sagernet/sing-tun/internal/tschecksum"
+
+func Checksum(buf []byte, initial uint16) uint16 {
+	return tschecksum.Checksum(buf, initial)
+}

internal/gtcpip/checksum/checksum_unsafe.go

@@ -1,3 +1,5 @@
+//go:build !amd64
+
 // Copyright 2023 The gVisor Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");