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xor.go
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xor.go
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// 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.
package kcp
import (
"runtime"
"unsafe"
)
const wordSize = int(unsafe.Sizeof(uintptr(0)))
const supportsUnaligned = runtime.GOARCH == "386" || runtime.GOARCH == "amd64" || runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" || runtime.GOARCH == "s390x"
// fastXORBytes xors in bulk. It only works on architectures that
// support unaligned read/writes.
func fastXORBytes(dst, a, b []byte) int {
n := len(a)
if len(b) < n {
n = len(b)
}
w := n / wordSize
if w > 0 {
wordBytes := w * wordSize
fastXORWords(dst[:wordBytes], a[:wordBytes], b[:wordBytes])
}
for i := (n - n%wordSize); i < n; i++ {
dst[i] = a[i] ^ b[i]
}
return n
}
func safeXORBytes(dst, a, b []byte) int {
n := len(a)
if len(b) < n {
n = len(b)
}
ex := n % 8
for i := 0; i < ex; i++ {
dst[i] = a[i] ^ b[i]
}
for i := ex; i < n; i += 8 {
dst[i] = a[i] ^ b[i]
dst[i+1] = a[i+1] ^ b[i+1]
dst[i+2] = a[i+2] ^ b[i+2]
dst[i+3] = a[i+3] ^ b[i+3]
dst[i+4] = a[i+4] ^ b[i+4]
dst[i+5] = a[i+5] ^ b[i+5]
dst[i+6] = a[i+6] ^ b[i+6]
dst[i+7] = a[i+7] ^ b[i+7]
}
return n
}
// xorBytes xors the bytes in a and b. The destination is assumed to have enough
// space. Returns the number of bytes xor'd.
func xorBytes(dst, a, b []byte) int {
if supportsUnaligned {
return fastXORBytes(dst, a, b)
} else {
// TODO(hanwen): if (dst, a, b) have common alignment
// we could still try fastXORBytes. It is not clear
// how often this happens, and it's only worth it if
// the block encryption itself is hardware
// accelerated.
return safeXORBytes(dst, a, b)
}
}
// fastXORWords XORs multiples of 4 or 8 bytes (depending on architecture.)
// The arguments are assumed to be of equal length.
func fastXORWords(dst, a, b []byte) {
dw := *(*[]uintptr)(unsafe.Pointer(&dst))
aw := *(*[]uintptr)(unsafe.Pointer(&a))
bw := *(*[]uintptr)(unsafe.Pointer(&b))
n := len(b) / wordSize
ex := n % 8
for i := 0; i < ex; i++ {
dw[i] = aw[i] ^ bw[i]
}
for i := ex; i < n; i += 8 {
dw[i] = aw[i] ^ bw[i]
dw[i+1] = aw[i+1] ^ bw[i+1]
dw[i+2] = aw[i+2] ^ bw[i+2]
dw[i+3] = aw[i+3] ^ bw[i+3]
dw[i+4] = aw[i+4] ^ bw[i+4]
dw[i+5] = aw[i+5] ^ bw[i+5]
dw[i+6] = aw[i+6] ^ bw[i+6]
dw[i+7] = aw[i+7] ^ bw[i+7]
}
}
func xorWords(dst, a, b []byte) {
if supportsUnaligned {
fastXORWords(dst, a, b)
} else {
safeXORBytes(dst, a, b)
}
}