It is a little unclear exactly what it is you are trying to do. How are you intending to use the Scan String.vi? What are your intended inputs and desired outputs? Are you seeing the desired performance with smaller numbers (less than 64 bits)? Are you getting an error or is the output of your routine not what you would expect? If the suggestion by GerdW do not do the trick, perhaps a screen shot of what you are trying to do and your current results would be helpful.