xor_generic.mx raw

   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  //go:build (!amd64 && !arm64 && !loong64 && !mips && !mipsle && !mips64 && !mips64le && !ppc64 && !ppc64le && !riscv64) || purego
   6  
   7  package subtle
   8  
   9  import (
  10  	"runtime"
  11  	"unsafe"
  12  )
  13  
  14  const wordSize = unsafe.Sizeof(uintptr(0))
  15  
  16  const supportsUnaligned = runtime.GOARCH == "386" ||
  17  	runtime.GOARCH == "amd64" ||
  18  	runtime.GOARCH == "ppc64" ||
  19  	runtime.GOARCH == "ppc64le" ||
  20  	runtime.GOARCH == "s390x"
  21  
  22  func xorBytes(dstb, xb, yb *byte, n int) {
  23  	// xorBytes assembly is written using pointers and n. Back to slices.
  24  	dst := unsafe.Slice(dstb, n)
  25  	x := unsafe.Slice(xb, n)
  26  	y := unsafe.Slice(yb, n)
  27  
  28  	if supportsUnaligned || aligned(dstb, xb, yb) {
  29  		xorLoop(words(dst), words(x), words(y))
  30  		if uintptr(n)%wordSize == 0 {
  31  			return
  32  		}
  33  		done := n &^ int(wordSize-1)
  34  		dst = dst[done:]
  35  		x = x[done:]
  36  		y = y[done:]
  37  	}
  38  	xorLoop(dst, x, y)
  39  }
  40  
  41  // aligned reports whether dst, x, and y are all word-aligned pointers.
  42  func aligned(dst, x, y *byte) bool {
  43  	return (uintptr(unsafe.Pointer(dst))|uintptr(unsafe.Pointer(x))|uintptr(unsafe.Pointer(y)))&(wordSize-1) == 0
  44  }
  45  
  46  // words returns a []uintptr pointing at the same data as x,
  47  // with any trailing partial word removed.
  48  func words(x []byte) []uintptr {
  49  	n := uintptr(len(x)) / wordSize
  50  	if n == 0 {
  51  		// Avoid creating a *uintptr that refers to data smaller than a uintptr;
  52  		// see issue 59334.
  53  		return nil
  54  	}
  55  	return unsafe.Slice((*uintptr)(unsafe.Pointer(&x[0])), n)
  56  }
  57  
  58  func xorLoop[T byte | uintptr](dst, x, y []T) {
  59  	x = x[:len(dst)] // remove bounds check in loop
  60  	y = y[:len(dst)] // remove bounds check in loop
  61  	for i := range dst {
  62  		dst[i] = x[i] ^ y[i]
  63  	}
  64  }
  65