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Side by Side Diff: src/pkg/crypto/cipher/xor.go

Issue 24250044: crypto/cipher: speed up xor operations in CBC, OBF, CTR... (Closed)
Patch Set: diff -r c8d3de543c1b https://code.google.com/p/go Created 10 years, 3 months ago
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1 // Copyright 2013 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4
5 package cipher
6
7 import (
8 "runtime"
9 "unsafe"
10 )
11
12 const wordSize = int(unsafe.Sizeof(uintptr(0)))
13 const supportsUnaligned = runtime.GOARCH == "386" || runtime.GOARCH == "amd64"
14
15 // fastXORBytes xors in bulk. It only works on architectures that
16 // support unaligned read/writes.
17 func fastXORBytes(dst, a, b []byte) int {
18 n := len(a)
19 if len(b) < n {
20 n = len(b)
21 }
22
23 w := n / wordSize
24 if w > 0 {
25 dw := *(*[]uintptr)(unsafe.Pointer(&dst))
26 aw := *(*[]uintptr)(unsafe.Pointer(&a))
27 bw := *(*[]uintptr)(unsafe.Pointer(&b))
28 for i := 0; i < w; i++ {
29 dw[i] = aw[i] ^ bw[i]
30 }
31 }
32
33 for i := (n - n%wordSize); i < n; i++ {
34 dst[i] = a[i] ^ b[i]
35 }
36
37 return n
38 }
39
40 func safeXORBytes(dst, a, b []byte) int {
41 n := len(a)
42 if len(b) < n {
43 n = len(b)
44 }
45 for i := 0; i < n; i++ {
46 dst[i] = a[i] ^ b[i]
47 }
48 return n
49 }
50
51 // xorBytes xors the bytes in a and b. The destination is assumed to have enough
52 // space. Returns the number of bytes xor'd.
53 func xorBytes(dst, a, b []byte) int {
54 if supportsUnaligned {
55 return fastXORBytes(dst, a, b)
56 } else {
57 // TODO(hanwen): if (dst, a, b) have common alignment
58 // we could still try fastXORBytes. It is not clear
59 // how often this happens, and it's only worth it if
60 // the block encryption itself is hardware
61 // accelerated.
62 return safeXORBytes(dst, a, b)
63 }
64 }
65
66 // fastXORWords XORs multiples of 4 or 8 bytes (depending on architecture.)
67 // The arguments are assumed to be of equal length.
68 func fastXORWords(dst, a, b []byte) {
69 dw := *(*[]uintptr)(unsafe.Pointer(&dst))
70 aw := *(*[]uintptr)(unsafe.Pointer(&a))
71 bw := *(*[]uintptr)(unsafe.Pointer(&b))
72 n := len(b) / wordSize
73 for i := 0; i < n; i++ {
74 dw[i] = aw[i] ^ bw[i]
75 }
76 }
77
78 func xorWords(dst, a, b []byte) {
79 if supportsUnaligned {
80 fastXORWords(dst, a, b)
81 } else {
82 safeXORBytes(dst, a, b)
83 }
84 }
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