1 files changed, 64 insertions, 0 deletions
diff --git a/src/crypto/subtle/xor_generic.go b/src/crypto/subtle/xor_generic.go
new file mode 100644
index 0000000..7dc89e3
--- /dev/null
+++ b/src/crypto/subtle/xor_generic.go
@@ -0,0 +1,64 @@
+// 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]
+	}
+}