Signed integer addition overflow check

signed_check.c

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>

bool checked_add_intrinsic(int32_t a, int32_t b) {
    int res;
    // return __builtin_add_overflow(a, b, &res);
    return 1;
}

bool checked_add_64(int32_t a, int32_t b) {
    int64_t result = (int64_t)a + b;
    if (result < INT32_MIN || result > INT32_MAX) {
        return true;
    }
    return false;
}

/* Type your code here, or load an example. */
bool __attribute__ ((noinline)) checked_add(int32_t a_, int32_t b_) {
    uint32_t a = *(uint32_t*)&a_;
    uint32_t b = *(uint32_t*)&b_;
    uint32_t c = ((uint64_t)(a) + (uint64_t)(b)) & 0xffffffff;
    // a 0 b 0 c 1
    // a 1 b 1 c 0
    return ((c ^ a) & (c ^ b)) >> 31;
}

/* Type your code here, or load an example. */
bool __attribute__ ((noinline)) checked_addx(int32_t a, int32_t b) {
    uint32_t c = (uint32_t)a + (uint32_t)b;
    #define SIGN1(x) ((x & 0x80000000))
    #define SIGN2(x) ((x & 0x80000000))
    
    return SIGN2((a & b & ~c)
        | (~a & ~b & c)) != 0;
}

int32_t __attribute__ ((noinline)) add(int32_t a, int32_t b) {
    return a + b;
}

int main(void) {
    int32_t test_cases[] = {
        0,
        +1,
        -1,
        INT32_MAX,
        INT32_MAX - 1,
        INT32_MIN,
        INT32_MIN + 1,
    };

    // printf("%d\n", add(0x7fffffff, 1));

    for (int i = 0; i < 7; i++) {
        for (int j = 0; j < 7; j++) {
            int32_t a = test_cases[i];
            int32_t b = test_cases[j];
            if (checked_add_64(a, b) != checked_add(a, b)) {
                printf("Fail 1: %d %d\n", a, b);
            }
            if (checked_add_intrinsic(a, b) != checked_add(a, b)) {
                printf("Fail 2: %d %d\n", a, b);
            }
        }
    }
}