Answer by Nick Dandoulakis for Why do people say there is modulo bias when using a random number generator?

Keep selecting a random is a good way to remove the bias.

Update

We could make the code fast if we search for an x in range divisible by n.

// Assumptions// rand() in [0, RAND_MAX]// n in (0, RAND_MAX]int x; // Keep searching for an x in a range divisible by n do {    x = rand();} while (x >= RAND_MAX - (RAND_MAX % n)) x %= n;

The above loop should be very fast, say 1 iteration on average.