Modulo arithmetic with signed integers undefined behavior in c?

Question

Having read all answers and comments in Should you always use 'int' for numbers in C, even if they are non-negative? I'm still not sure what to do in the following situation.

Two remote devices are counting events at their respective location. They regularly report the counter readings to a PC where a feedback algorithm somehow keeps the difference of the counter readings within bounds. The sequences of events are endless so that the readings are reported modulo 2^n. For modulo arithmetic unsigned integers are suggested. The difference, however, may well become negative. Casting the readings to signed integers before calculating the difference works fine on the platform I tested it on (that is, I get the differences modulo 2^n with values small in magnitude). Declaring the readings as signed already in the interface yields elegant code. However, the code shall be portable. Shall I take the U.B. warning seriously?

Answer 1

Shall I take the U.B. warning seriously?

If you don't want your compiler or CPU play tricks on you, your code should be UB-free.