cintegeroverflowint32uint32-t

I need to find maximum int32_t number without using constants like INT32_MAX, INT_MAX, etc

So I have a task to check for overflow when adding two int32_t numbers. In case of overflow my function must return maximum or minimum number of int32_t, depending on the sign of overflow, but using constants like UINT32_MAX is restricted. How do I do that? Here's the code if it will help you:

#include "inttypes.h"

int32_t
satsum(int32_t v1, int32_t v2) {
    int32_t res = 0;
    if(__builtin_sadd_overflow(v1, v2, &res)) {
        if (res < 0) {
            return ?
        }
        return ?
    } else {
        res = v1 + v2;
        return res;
    }
}
Solution

  • The value of INT32_MAX (maximum value of int32_t) and INT32_MIN (minimum value of int32_t) are defined in C specification, so you can write the values instead of using the constants.

    Quote from N1570 7.20.2.1 Limits of exact-width integer types:

    — minimum values of exact-width signed integer types
    INTN_MIN exactly −(2N-1)
    — maximum values of exact-width signed integer types
    INTN_MAX exactly 2N−1 − 1
    — maximum values of exact-width unsigned integer types
    UINTN_MAX exactly 2N − 1

    Here is one point: 2N can be represented as 1<<N, but 1<<31 will cause overflow, so you should use ((1<<30)-1)*2+1 instead of 1<<31.

    Also you should use INT32_C macor to use literals of int32_t instead of int.

    In conclusion, what you should use are: