thanks a lot again, nihil...

the first link was interesting, reminded me to poke around the /usr/include/limits.h file. I found that a constant _WORDSIZE in bits/wordsize.h that would determine the max size of long unsigned. I'm on a 32 bit system, so that makes it 2**32-1. But I don't think that would depend upon the compiler if I'm using the new compilers that conform to the latest C++ standards. Maybe it would have been a different matter if I was using something like Borland Turbo!

I have previously worked with GMP, but found the documentation quite cumbersome to follow