ip报文的分片机制 解析中 学得胃疼。。。

tcpip/network/hash/hash.go

@@ -0,0 +1,70 @@
+package hash
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"netstack/tcpip/header"
+)
+
+var hashIV = RandN32(1)[0]
+
+// RandN32 生成 n 个加密随机 32 位数字的切片
+func RandN32(n int) []uint32 {
+	b := make([]byte, 4*n)
+	if _, err := rand.Read(b); err != nil {
+		panic("unable to get random numbers: " + err.Error())
+	}
+	r := make([]uint32, n)
+	for i := range r {
+		r[i] = binary.LittleEndian.Uint32(b[4*i : (4*i + 4)])
+	}
+	return r
+}
+
+func Hash3Words(a, b, c, initval uint32) uint32 {
+	const iv = 0xdeadbeef + (3 << 2)
+	initval += iv
+
+	a += initval
+	b += initval
+	c += initval
+
+	c ^= b
+	c -= rol32(b, 14)
+	a ^= c
+	a -= rol32(c, 11)
+	b ^= a
+	b -= rol32(a, 25)
+	c ^= b
+	c -= rol32(b, 16)
+	a ^= c
+	a -= rol32(c, 4)
+	b ^= a
+	b -= rol32(a, 14)
+	c ^= b
+	c -= rol32(b, 24)
+
+	return c
+}
+
+// 根据id，源ip，目的ip和协议类型得到hash值
+func IPv4FragmentHash(h header.IPv4) uint32 {
+	x := uint32(h.ID())<<16 | uint32(h.Protocol())
+	t := h.SourceAddress()
+	y := uint32(t[0]) | uint32(t[1])<<8 | uint32(t[2])<<16 | uint32(t[3])<<24
+	t = h.DestinationAddress()
+	z := uint32(t[0]) | uint32(t[1])<<8 | uint32(t[2])<<16 | uint32(t[3])<<24
+	return Hash3Words(x, y, z, hashIV)
+}
+
+func IPv6FragmentHash(h header.IPv6, f header.IPv6Fragment) uint32 {
+	t := h.SourceAddress()
+	y := uint32(t[0]) | uint32(t[1])<<8 | uint32(t[2])<<16 | uint32(t[3])<<24
+	t = h.DestinationAddress()
+	z := uint32(t[0]) | uint32(t[1])<<8 | uint32(t[2])<<16 | uint32(t[3])<<24
+	return Hash3Words(f.ID(), y, z, hashIV)
+}
+
+func rol32(v, shift uint32) uint32 {
+	return (v << shift) | (v >> ((-shift) & 31))
+}