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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.
//go:build (!amd64 && !arm64 && !ppc64 && !ppc64le) || purego
package subtle
import (
"runtime"
"unsafe"
)
const wordSize = unsafe.Sizeof(uintptr(0))
const supportsUnaligned = runtime.GOARCH == "386" ||
runtime.GOARCH == "amd64" ||
runtime.GOARCH == "ppc64" ||
runtime.GOARCH == "ppc64le" ||
runtime.GOARCH == "s390x"
func xorBytes(dstb, xb, yb *byte, n int) {
// xorBytes assembly is written using pointers and n. Back to slices.
dst := unsafe.Slice(dstb, n)
x := unsafe.Slice(xb, n)
y := unsafe.Slice(yb, n)
if supportsUnaligned || aligned(dstb, xb, yb) {
xorLoop(words(dst), words(x), words(y))
if uintptr(n)%wordSize == 0 {
return
}
done := n &^ int(wordSize-1)
dst = dst[done:]
x = x[done:]
y = y[done:]
}
xorLoop(dst, x, y)
}
// aligned reports whether dst, x, and y are all word-aligned pointers.
func aligned(dst, x, y *byte) bool {
return (uintptr(unsafe.Pointer(dst))|uintptr(unsafe.Pointer(x))|uintptr(unsafe.Pointer(y)))&(wordSize-1) == 0
}
// words returns a []uintptr pointing at the same data as x,
// with any trailing partial word removed.
func words(x []byte) []uintptr {
n := uintptr(len(x)) / wordSize
if n == 0 {
// Avoid creating a *uintptr that refers to data smaller than a uintptr;
// see issue 59334.
return nil
}
return unsafe.Slice((*uintptr)(unsafe.Pointer(&x[0])), n)
}
func xorLoop[T byte | uintptr](dst, x, y []T) {
x = x[:len(dst)] // remove bounds check in loop
y = y[:len(dst)] // remove bounds check in loop
for i := range dst {
dst[i] = x[i] ^ y[i]
}
}
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