Most (all?) modern processors have instructions and flags specifically for querying and reacting to integer overflow/carry.
This seems like a situation where dropping to assembly to perform the addition and testing the flag makes sense. GCC has a mechanism for inline assembly where you list the variables you read from, you write to, and registers you modify and the optimizer plays nice with you. You could provide it as a function to use instead of doing the addition in C.
This seems like a situation where dropping to assembly to perform the addition and testing the flag makes sense. GCC has a mechanism for inline assembly where you list the variables you read from, you write to, and registers you modify and the optimizer plays nice with you. You could provide it as a function to use instead of doing the addition in C.