You can't ever check for (signed) overflows in C - you can only prevent them. I'm not sure if I'm drawing a distinction you weren't intending to make (if so, th

You can't ever check for (signed) overflows in C - you can only prevent them. I'm not sure if I'm drawing a distinction you weren't intending to make (if so, then my apologies). When you are adding signed integers in C, you need to prove that doing so can't overflow - knowing the exact width doesn't really help you here - just prove it for the narrowest possible width and you have proved it for all of them. In practice this isn't hard because either it is trivial to prove (e.g. incrementing a variable which is known to be small, or just plain modifying the code to put in explicit saturation/other logic for the cases where things get hairy) Of course an 8-bit compiler is going to allocate 32-bits for a long int - the language requires that a long is at least 32-bits wide. If you had a compiler that didn't do this, then it isn't a C compiler.