My guess is: The `(T, bool)` that gets returned is friendly towards optimization. If you don't use the bool, the overflowing arithmetic is reduced to efficien

My guess is: The `(T, bool)` that gets returned is friendly towards optimization. If you don't use the bool, the overflowing arithmetic is reduced to efficient arithmetic which is overflowing by default. If you do use the bool, the generated code contains one extra instruction.