What is an efficient way to get the least non-negative residue modulo n in C?

Question

Is there an efficient way to get the least non-negative residue modulo n, where n is positive, in C?

This is quite easy if the number is non-negative, then it\'s jus

Answer 1

You could simply check if the result is negative and then act accordingly:

int mod(int n, int m) {
   int r = n % m;
   if (r < 0)
      return r + m;
   else
      return r;
}

Or, without if-then-else and as a single expression:

r = ((n % m) + m) % m;