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// Copyright 2022 The Pion Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package xor provides utility functions used by other Pion
// packages. ARM arch.
package xor
import (
"golang.org/x/sys/cpu"
"unsafe"
)
const wordSize = int(unsafe.Sizeof(uintptr(0))) // nolint:gosec
var hasNEON = cpu.ARM.HasNEON // nolint:gochecknoglobals
func isAligned(a *byte) bool {
return uintptr(unsafe.Pointer(a))%uintptr(wordSize) == 0
}
// XorBytes xors the bytes in a and b. The destination should have enough
// space, otherwise xorBytes will panic. Returns the number of bytes xor'd.
//revive:disable-next-line
func XorBytes(dst, a, b []byte) int {
n := len(a)
if len(b) < n {
n = len(b)
}
if n == 0 {
return 0
}
// make sure dst has enough space
_ = dst[n-1]
if hasNEON {
xorBytesNEON32(&dst[0], &a[0], &b[0], n)
} else if isAligned(&dst[0]) && isAligned(&a[0]) && isAligned(&b[0]) {
xorBytesARM32(&dst[0], &a[0], &b[0], n)
} else {
safeXORBytes(dst, a, b, n)
}
return n
}
// n needs to be smaller or equal than the length of a and b.
func safeXORBytes(dst, a, b []byte, n int) {
for i := 0; i < n; i++ {
dst[i] = a[i] ^ b[i]
}
}
//go:noescape
func xorBytesARM32(dst, a, b *byte, n int)
//go:noescape
func xorBytesNEON32(dst, a, b *byte, n int)
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