Well your result is only going to be limited to 255, if it is a one-byte unsigned number. If it is a 16 bit or 32 bit number, there is nothing specifically limiting it to a maximum value of 255.
I had a look at the code there and could not determine how exactly these numbers are being derived.
If that is a problem for you, you can always scale it back to the 0..255 range if you want to use it for some other purpose.