code: 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
  }
docs: // fastXORBytes xors in bulk. It only works on architectures that support
  // unaligned read/writes.