How to avoid overflow in expr. A * B - C * D

Question

I need to compute an expression which looks like: A*B - C*D, where their types are: signed long long int A, B, C, D; Each number can be really big (not

Answer 1

You could consider computing a greatest common factor for all your values, and then dividing them by that factor before doing your arithmetic operations, then multiplying again. This assumes that such a factor exists, however (for example, if A, B, C and D happen to be relatively prime, they won't have a common factor).

Similarly, you could consider working on log-scales, but this is going to be a little scary, subject to numerical precision.