testing add overflow in C

test_addv.c

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

// yes, it breaks. Clearly Zig has better semantics, as it utilizes LLVM.

int32_t addv(int32_t a, int32_t b)
{
  uint32_t usum = (uint32_t)a + (uint32_t)b;
  int32_t isum = (int32_t)usum;
  if (((isum ^ a) & (isum ^ b)) < 0)
      return -5;
  return isum;
}

int32_t simpler_addv(int32_t a, int32_t b)
{
  int64_t c;
  c = (int64_t)a + (int64_t)b;
  if (c < INT32_MIN || c > INT32_MAX)
    return -5;
  return c;
}


int main() {
  int32_t a = INT32_MIN;
  int32_t b = INT32_MIN;
  int32_t step = 1000;
  for(;a < INT32_MAX; a+=step)
  {
    for(;b < INT32_MAX; b+=step)
    {
      int32_t expect = simpler_addv(a,b);
      int32_t real = addv(a, b);
      if(expect != real)
        printf("example broken\n");
    }
  }
}