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 } 85
