func xorBytes(dst, a, b []byte) int {
	if supportsUnaligned {
		return fastXORBytes(dst, a, b)
	}
	return safeXORBytes(dst, a, b)
}
xorBytes xors the bytes in a and b. The destination is assumed to have enough
space. Returns the number of bytes xor'd.
package stun
import (
	"runtime"
	"unsafe"
)
const wordSize = int(unsafe.Sizeof(uintptr(0)))
var supportsUnaligned = runtime.GOARCH == "386" || runtime.GOARCH == "amd64"
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
}
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
}