common/bitutil: deprecate XORBytes in favor of stdlib crypto/subtle

common/bitutil/bitutil.go

@@ -8,49 +8,23 @@
 package bitutil
 
 import (
+	"crypto/subtle"
 	"runtime"
 	"unsafe"
 )
 
 const wordSize = int(unsafe.Sizeof(uintptr(0)))
 const supportsUnaligned = runtime.GOARCH == "386" || runtime.GOARCH == "amd64" || runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" || runtime.GOARCH == "s390x"
 
-// XORBytes xors the bytes in a and b. The destination is assumed to have enough
-// space. Returns the number of bytes xor'd.
+// XORBytes xors the bytes in a and b and writes the result into dst.
+// The number of bytes XORed is min(len(a), len(b)), and that value is returned.
+//
+// dst must have length >= min(len(a), len(b)) or the function will panic.
+// dst may exactly overlap with a or with b, but partial overlaps are not allowed.
+//
+// Deprecated: use crypto/subtle.XORBytes.
 func XORBytes(dst, a, b []byte) int {
-	if supportsUnaligned {
-		return fastXORBytes(dst, a, b)
-	}
-	return safeXORBytes(dst, a, b)
-}
-
-// fastXORBytes xors in bulk. It only works on architectures that support
-// unaligned read/writes.
-func fastXORBytes(dst, a, b []byte) int {
-	n := min(len(b), len(a))
-	w := n / wordSize
-	if w > 0 {
-		dw := *(*[]uintptr)(unsafe.Pointer(&dst))
-		aw := *(*[]uintptr)(unsafe.Pointer(&a))
-		bw := *(*[]uintptr)(unsafe.Pointer(&b))
-		for i := 0; i < w; i++ {
-			dw[i] = aw[i] ^ bw[i]
-		}
-	}
-	for i := n - n%wordSize; i < n; i++ {
-		dst[i] = a[i] ^ b[i]
-	}
-	return n
-}
-
-// safeXORBytes xors one by one. It works on all architectures, independent if
-// it supports unaligned read/writes or not.
-func safeXORBytes(dst, a, b []byte) int {
-	n := min(len(b), len(a))
-	for i := 0; i < n; i++ {
-		dst[i] = a[i] ^ b[i]
-	}
-	return n
+	return subtle.XORBytes(dst, a, b)
 }
 
 // ANDBytes ands the bytes in a and b. The destination is assumed to have enough

common/bitutil/bitutil_test.go

@@ -29,7 +29,7 @@ func TestXOR(t *testing.T) {
 				d2 := make([]byte, 1023+alignD)[alignD:]
 
 				XORBytes(d1, p, q)
-				safeXORBytes(d2, p, q)
+				naiveXOR(d2, p, q)
 				if !bytes.Equal(d1, d2) {
 					t.Error("not equal", d1, d2)
 				}
@@ -38,6 +38,15 @@ func TestXOR(t *testing.T) {
 	}
 }
 
+// naiveXOR xors bytes one by one.
+func naiveXOR(dst, a, b []byte) int {
+	n := min(len(b), len(a))
+	for i := range n {
+		dst[i] = a[i] ^ b[i]
+	}
+	return n
+}
+
 // Tests that bitwise AND works for various alignments.
 func TestAND(t *testing.T) {
 	for alignP := 0; alignP < 2; alignP++ {
@@ -136,7 +145,7 @@ func benchmarkBaseXOR(b *testing.B, size int) {
 	p, q := make([]byte, size), make([]byte, size)
 
 	for i := 0; i < b.N; i++ {
-		safeXORBytes(p, p, q)
+		naiveXOR(p, p, q)
 	}
 }
 

execution/protocol/rules/ethash/algorithm.go

@@ -20,6 +20,7 @@
 package ethash
 
 import (
+	"crypto/subtle"
 	"encoding/binary"
 	"hash"
 	"math/big"
@@ -33,7 +34,6 @@ import (
 	"golang.org/x/crypto/sha3"
 
 	"github.com/erigontech/erigon/common"
-	"github.com/erigontech/erigon/common/bitutil"
 	"github.com/erigontech/erigon/common/crypto"
 	"github.com/erigontech/erigon/common/dbg"
 	"github.com/erigontech/erigon/common/length"
@@ -239,7 +239,7 @@ func generateCache(dest []uint32, epoch uint64, seed []byte) {
 				dstOff = j * hashBytes
 				xorOff = (binary.LittleEndian.Uint32(cache[dstOff:]) % uint32(rows)) * hashBytes
 			)
-			bitutil.XORBytes(temp, cache[srcOff:srcOff+hashBytes], cache[xorOff:xorOff+hashBytes])
+			subtle.XORBytes(temp, cache[srcOff:srcOff+hashBytes], cache[xorOff:xorOff+hashBytes])
 			keccak512(cache[dstOff:], temp)
 
 			atomic.AddUint32(&progress, 1)