1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
|
// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Modifications copyright 2022 The Pion Authors, governed by
// the MIT license.
//go:build !amd64 && !ppc64 && !ppc64le && !arm64 && !arm
// Package xor provides utility functions used by other Pion
// packages. Generic arch.
package xor
import (
"runtime"
"unsafe"
)
const wordSize = int(unsafe.Sizeof(uintptr(0))) // nolint:gosec
const supportsUnaligned = runtime.GOARCH == "386" || runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" || runtime.GOARCH == "s390x" // nolint:gochecknoglobals
func isAligned(a *byte) bool {
return uintptr(unsafe.Pointer(a))%uintptr(wordSize) == 0
}
// XorBytes xors the bytes in a and b. The destination should have enough
// space, otherwise xorBytes will panic. Returns the number of bytes xor'd.
//revive:disable-next-line
func XorBytes(dst, a, b []byte) int {
n := len(a)
if len(b) < n {
n = len(b)
}
if n == 0 {
return 0
}
switch {
case supportsUnaligned:
fastXORBytes(dst, a, b, n)
case isAligned(&dst[0]) && isAligned(&a[0]) && isAligned(&b[0]):
fastXORBytes(dst, a, b, n)
default:
safeXORBytes(dst, a, b, n)
}
return n
}
// fastXORBytes xors in bulk. It only works on architectures that
// support unaligned read/writes.
// n needs to be smaller or equal than the length of a and b.
func fastXORBytes(dst, a, b []byte, n int) {
// Assert dst has enough space
_ = dst[n-1]
w := n / wordSize
if w > 0 {
dw := *(*[]uintptr)(unsafe.Pointer(&dst)) // nolint:gosec
aw := *(*[]uintptr)(unsafe.Pointer(&a)) // nolint:gosec
bw := *(*[]uintptr)(unsafe.Pointer(&b)) // nolint:gosec
for i := 0; i < w; i++ {
dw[i] = aw[i] ^ bw[i]
}
}
for i := (n - n%wordSize); i < n; i++ {
dst[i] = a[i] ^ b[i]
}
}
// n needs to be smaller or equal than the length of a and b.
func safeXORBytes(dst, a, b []byte, n int) {
for i := 0; i < n; i++ {
dst[i] = a[i] ^ b[i]
}
}
|
