code: func base64NeededDecodedLength(n int) int {
  	// Returns -1 indicate the result will overflow.
  	if strconv.IntSize == 64 && n > math.MaxInt64/3 {
  		return -1
  	}
  	if strconv.IntSize == 32 && n > math.MaxInt32/3 {
  		return -1
  	}
  	return n * 3 / 4
  }
docs: // base64NeededDecodedLength return the base64 decoded string length.