How Should You Write a Fast Integer Overflow Check?(blog.regehr.org)

    if (r > 0
            ? l > Integer.MAX_VALUE - r
            : l < Integer.MIN_VALUE - r)
        throw new ArithmeticException(String.format(
                "Integer overflow: %d + %d", l, r));
    return l + r;

    int checked_add_n(int_t a, int_t b, int_t *rp) {
        uint_t s = (uint_t)a + (uint_t)b;
        *rp = s;
        return ((a ^ s)&(b ^ s)) >> (BITS - 1);
    }

    ci = s ^ a ^ b; // upper bit of ci contains the relevant bit

    co = ci&a ^ ci&b ^ a&b;

  #define BITS (8*sizeof(int))-1

  int checked_add(int a, int b, int *rp)
  {
      *rp = a+b;
      
      return (a^b) < 0 ? 0 : (a^(*rp)) < 0  ? 1 : 0) ;
  }

  #include <stdio.h>
  #include <time.h>
  #include <stdlib.h>

  #define BITS (8*sizeof(int))-1

  int checked_add2(int a, int b, int *rp) {
    uint ur = (uint)a + (uint)b;
    uint sr = ur >> (BITS-1);
    uint sa = (uint)a >> (BITS-1);
    uint sb = (uint)b >> (BITS-1);
    *rp = ur;
    return
      (sa && sb && !sr) ||
      (!sa && !sb && sr);
  }


  int checked_add(int a, int b, int *rp)
  {
      *rp = a+b;
      return ((a^b) | (a^(*rp)) < 0)  ? 1 : 0 ;
  }


  int main(int argc, char* argv[])
  {
      int a, b, c;
      long clong;
      srand(time(NULL));


      for(unsigned int i = 0; i < 50000000; ++i)
      {
          bool overflow = false;
          a = rand();
          b = rand();
          clong = (long)a + (long)b;

          overflow = checked_add(a,b,&c);

          if(clong != (long)c && !overflow)
              printf("Overflow not detected %i + %i = %i \n", a, b, c);

      }

      return 0;
  }