best way to recognize and handle integer overflow in c?

Question

I am so new in C and so far I didn't comprehend how to prevent from integer overflow, I read many articles but still I am not 100% sure! in this case

int ft_sqrt(int nb)
{
    long int    sqrt;
    
    if (nb <= 0)
        return (0);
    if (nb == 1)
        return (1); 
    sqrt = 1;
    while (sqrt * sqrt < nb)
    {
        sqrt++;
    }
    if (sqrt * sqrt == nb)
        return (sqrt);
    else
        return (0);
}

to prevent overflow should I use

long

? what is the best practice to do that?

Answer 1

long is not certainly wider than int and so its use may not widen the computation.

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To certainly avoid overflow, don't multiple, but divide.

int ft_sqrt(int nb) {
    int    sqrt;
    if (nb <= 0)
        return (0);
    if (nb == 1)
        return (1); 
    sqrt = 1;
    // while (sqrt * sqrt < nb)
    while (sqrt < nb / sqrt) {
        sqrt++;
    }
    if (sqrt == nb / sqrt)
        return (sqrt);
    else
        return (0);
}

---

Yes code takes a performance hit - yet OP algorithm has many ways for improvement)

---

Alternate code:

unsigned bit_width(unsigned x) {
  unsigned width = 0;
  while (x) {
    x /= 2;
    width++;
  }
  return width;
}

unsigned usqrt(unsigned x) {
  if (x == 0) {
    return 0;
  }
  unsigned y = 1u << bit_width(x) / 2;
  unsigned y_previous;
  unsigned diff;
  unsigned diff1count = 0;

  do {
    y_previous = y;
    y = (y + x / y) / 2;
    diff = y_previous < y ? y - y_previous : y_previous - y;
    if (diff == 1)
      diff1count++;
  } while (diff > 1 || (diff == 1 && diff1count <= 1));
  y = (y_previous + y) / 2;
  return y;
}