overflow.c

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

int add_i64(int64_t a, int64_t b, int64_t* r)
{
    volatile int overflow = 1;
    volatile int64_t result = a + b;

    asm volatile
    (
     "jno 1f          ;"
     "movl $0, %[xo]  ;"
     "1:              ;"
     : [xo] "=m" (overflow)
     );

    if(r)
        *r = result;

    return overflow;
}


void main() {
    int64_t a,b,x,y,z;
    int64_t r = 0;
    int c;
    a = 536870919;
    b = 2147483647;
    x = 2305843009213693952;
    y = -498763014;
    z = 6917529027641081856;
    c = add_i64(a,b,&r);
    if (!c) {
        printf("Integer overflow detected adding %"PRIi64" and %"PRIi64"\n", a, b);
    } else {
        printf("result = %"PRIi64"\n", r);
    }
    r = 0;
    c = add_i64(x,y,&r);
    if (!c) {
        printf("Integer overflow detected adding %"PRIi64" and %"PRIi64"\n", x, y);
    } else {
        printf("result = %"PRIi64"\n", r);
    }
    r = 0;
    c = add_i64(z,x,&r);
    if (!c) {
        printf("Integer overflow detected adding %"PRIi64" and %"PRIi64"\n", z, x);
    } else {
        printf("result = %"PRIi64"\n", r);
    }
}