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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.
// Adapted from: https://golang.org/src/crypto/cipher/xor.go
// Package bitutil implements fast bitwise operations.
package bitutil
import (
"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.
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 := len(a)
if len(b) < n {
n = len(b)
}
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 := len(a)
if len(b) < n {
n = len(b)
}
for i := 0; i < n; i++ {
dst[i] = a[i] ^ b[i]
}
return n
}
// ANDBytes ands the bytes in a and b. The destination is assumed to have enough
// space. Returns the number of bytes and'd.
func ANDBytes(dst, a, b []byte) int {
if supportsUnaligned {
return fastANDBytes(dst, a, b)
}
return safeANDBytes(dst, a, b)
}
// fastANDBytes ands in bulk. It only works on architectures that support
// unaligned read/writes.
func fastANDBytes(dst, a, b []byte) int {
n := len(a)
if len(b) < n {
n = len(b)
}
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
}
// safeANDBytes ands one by one. It works on all architectures, independent if
// it supports unaligned read/writes or not.
func safeANDBytes(dst, a, b []byte) int {
n := len(a)
if len(b) < n {
n = len(b)
}
for i := 0; i < n; i++ {
dst[i] = a[i] & b[i]
}
return n
}
// ORBytes ors the bytes in a and b. The destination is assumed to have enough
// space. Returns the number of bytes or'd.
func ORBytes(dst, a, b []byte) int {
if supportsUnaligned {
return fastORBytes(dst, a, b)
}
return safeORBytes(dst, a, b)
}
// fastORBytes ors in bulk. It only works on architectures that support
// unaligned read/writes.
func fastORBytes(dst, a, b []byte) int {
n := len(a)
if len(b) < n {
n = len(b)
}
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
}
// safeORBytes ors one by one. It works on all architectures, independent if
// it supports unaligned read/writes or not.
func safeORBytes(dst, a, b []byte) int {
n := len(a)
if len(b) < n {
n = len(b)
}
for i := 0; i < n; i++ {
dst[i] = a[i] | b[i]
}
return n
}
// TestBytes tests whether any bit is set in the input byte slice.
func TestBytes(p []byte) bool {
if supportsUnaligned {
return fastTestBytes(p)
}
return safeTestBytes(p)
}
// fastTestBytes tests for set bits in bulk. It only works on architectures that
// support unaligned read/writes.
func fastTestBytes(p []byte) bool {
n := len(p)
w := n / wordSize
if w > 0 {
pw := *(*[]uintptr)(unsafe.Pointer(&p))
for i := 0; i < w; i++ {
if pw[i] != 0 {
return true
}
}
}
for i := n - n%wordSize; i < n; i++ {
if p[i] != 0 {
return true
}
}
return false
}
// safeTestBytes tests for set bits one byte at a time. It works on all
// architectures, independent if it supports unaligned read/writes or not.
func safeTestBytes(p []byte) bool {
for i := 0; i < len(p); i++ {
if p[i] != 0 {
return true
}
}
return false
}
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