> * Finally (and this will probably be controversial), use unsigned arithmetic as much as you can! The reason for this is because unsigned arithmetic has far fewer cases of UB, and with a little work, you can simulate two's-complement signed arithmetic in C without UB.

I would recommend against this. You're trading off one form of incorrect behavior (UB) for another form of incorrect behavior (wraparound on overflow is incorrect >99% of the time), with the added potential for mistakes in the emulation step.

Instead, do this:

* If you consider that wraparound on overflow is in fact the correct and desired behavior, use unsigned arithmetic.

* If you want to check for overflowing conditions, use your compiler's builtins for checked operations (C23 finally adds ckd_* ops, but it's too new to recommend use of yet).