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320c4a6448
For #69536 Change-Id: I2d7b6e7b9932d0f0f582a5ab0bb871395dc2a1e8 Reviewed-on: https://go-review.googlesource.com/c/go/+/626675 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Daniel McCarney <daniel@binaryparadox.net> Reviewed-by: Roland Shoemaker <roland@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Auto-Submit: Filippo Valsorda <filippo@golang.org>
62 lines
1.6 KiB
Go
62 lines
1.6 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 subtle
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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 = unsafe.Sizeof(uintptr(0))
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const supportsUnaligned = runtime.GOARCH == "386" ||
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runtime.GOARCH == "amd64" ||
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runtime.GOARCH == "ppc64" ||
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runtime.GOARCH == "ppc64le" ||
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runtime.GOARCH == "s390x"
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func xorBytes(dstb, xb, yb *byte, n int) {
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// xorBytes assembly is written using pointers and n. Back to slices.
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dst := unsafe.Slice(dstb, n)
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x := unsafe.Slice(xb, n)
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y := unsafe.Slice(yb, n)
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if supportsUnaligned || aligned(dstb, xb, yb) {
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xorLoop(words(dst), words(x), words(y))
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if uintptr(n)%wordSize == 0 {
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return
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}
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done := n &^ int(wordSize-1)
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dst = dst[done:]
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x = x[done:]
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y = y[done:]
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}
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xorLoop(dst, x, y)
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}
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// aligned reports whether dst, x, and y are all word-aligned pointers.
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func aligned(dst, x, y *byte) bool {
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return (uintptr(unsafe.Pointer(dst))|uintptr(unsafe.Pointer(x))|uintptr(unsafe.Pointer(y)))&(wordSize-1) == 0
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}
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// words returns a []uintptr pointing at the same data as x,
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// with any trailing partial word removed.
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func words(x []byte) []uintptr {
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n := uintptr(len(x)) / wordSize
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if n == 0 {
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// Avoid creating a *uintptr that refers to data smaller than a uintptr;
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// see issue 59334.
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return nil
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}
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return unsafe.Slice((*uintptr)(unsafe.Pointer(&x[0])), n)
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}
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func xorLoop[T byte | uintptr](dst, x, y []T) {
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x = x[:len(dst)] // remove bounds check in loop
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y = y[:len(dst)] // remove bounds check in loop
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for i := range dst {
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dst[i] = x[i] ^ y[i]
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}
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} |