mirror of
https://github.com/octoleo/syncthing.git
synced 2024-11-14 17:24:04 +00:00
111 lines
2.5 KiB
Go
111 lines
2.5 KiB
Go
// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package kcp
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import (
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"runtime"
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"unsafe"
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)
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const wordSize = int(unsafe.Sizeof(uintptr(0)))
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const supportsUnaligned = runtime.GOARCH == "386" || runtime.GOARCH == "amd64" || runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" || runtime.GOARCH == "s390x"
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// fastXORBytes xors in bulk. It only works on architectures that
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// support unaligned read/writes.
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func fastXORBytes(dst, a, b []byte) int {
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n := len(a)
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if len(b) < n {
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n = len(b)
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}
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w := n / wordSize
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if w > 0 {
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wordBytes := w * wordSize
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fastXORWords(dst[:wordBytes], a[:wordBytes], b[:wordBytes])
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}
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for i := (n - n%wordSize); i < n; i++ {
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dst[i] = a[i] ^ b[i]
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}
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return n
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}
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func safeXORBytes(dst, a, b []byte) int {
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n := len(a)
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if len(b) < n {
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n = len(b)
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}
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ex := n % 8
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for i := 0; i < ex; i++ {
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dst[i] = a[i] ^ b[i]
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}
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for i := ex; i < n; i += 8 {
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_dst := dst[i : i+8]
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_a := a[i : i+8]
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_b := b[i : i+8]
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_dst[0] = _a[0] ^ _b[0]
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_dst[1] = _a[1] ^ _b[1]
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_dst[2] = _a[2] ^ _b[2]
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_dst[3] = _a[3] ^ _b[3]
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_dst[4] = _a[4] ^ _b[4]
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_dst[5] = _a[5] ^ _b[5]
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_dst[6] = _a[6] ^ _b[6]
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_dst[7] = _a[7] ^ _b[7]
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}
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return n
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}
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// xorBytes xors the bytes in a and b. The destination is assumed to have enough
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// space. Returns the number of bytes xor'd.
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func xorBytes(dst, a, b []byte) int {
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if supportsUnaligned {
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return fastXORBytes(dst, a, b)
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}
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// TODO(hanwen): if (dst, a, b) have common alignment
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// we could still try fastXORBytes. It is not clear
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// how often this happens, and it's only worth it if
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// the block encryption itself is hardware
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// accelerated.
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return safeXORBytes(dst, a, b)
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}
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// fastXORWords XORs multiples of 4 or 8 bytes (depending on architecture.)
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// The arguments are assumed to be of equal length.
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func fastXORWords(dst, a, b []byte) {
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dw := *(*[]uintptr)(unsafe.Pointer(&dst))
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aw := *(*[]uintptr)(unsafe.Pointer(&a))
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bw := *(*[]uintptr)(unsafe.Pointer(&b))
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n := len(b) / wordSize
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ex := n % 8
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for i := 0; i < ex; i++ {
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dw[i] = aw[i] ^ bw[i]
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}
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for i := ex; i < n; i += 8 {
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_dw := dw[i : i+8]
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_aw := aw[i : i+8]
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_bw := bw[i : i+8]
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_dw[0] = _aw[0] ^ _bw[0]
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_dw[1] = _aw[1] ^ _bw[1]
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_dw[2] = _aw[2] ^ _bw[2]
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_dw[3] = _aw[3] ^ _bw[3]
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_dw[4] = _aw[4] ^ _bw[4]
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_dw[5] = _aw[5] ^ _bw[5]
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_dw[6] = _aw[6] ^ _bw[6]
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_dw[7] = _aw[7] ^ _bw[7]
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}
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}
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func xorWords(dst, a, b []byte) {
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if supportsUnaligned {
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fastXORWords(dst, a, b)
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} else {
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safeXORBytes(dst, a, b)
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}
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}
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