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// Copyright 2017 The Netstack Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package hash contains utility functions for hashing.
package hash
import (
"encoding/binary"
"gvisor.googlesource.com/gvisor/pkg/rand"
"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
)
var hashIV = RandN32(1)[0]
// RandN32 generates a slice of n cryptographic random 32-bit numbers.
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
}
// Hash3Words calculates the Jenkins hash of 3 32-bit words. This is adapted
// from linux.
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
}
// IPv4FragmentHash computes the hash of the IPv4 fragment as suggested in RFC 791.
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)
}
// IPv6FragmentHash computes the hash of the ipv6 fragment.
// Unlike IPv4, the protocol is not used to compute the hash.
// RFC 2640 (sec 4.5) is not very sharp on this aspect.
// As a reference, also Linux ignores the protocol to compute
// the hash (inet6_hash_frag).
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))
}
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