The issue is that overflow on signed is UB. I can count final decimal places(ptr - start_ptr) to check if it is larger than the maximum digits allowed. This i

The issue is that overflow on signed is UB. I can count final decimal places(ptr - start_ptr) to check if it is larger than the maximum digits allowed. This is cheap as the check is after the parse. Throw in a floor(log10( result )) == diff or something like that too.