Comment by kleiba2

    for (int i = 0; i < 1000; i++) {
        small_numbers[smlen] = numbers[i];
        smlen += (numbers[i] < 500);
    }
 

is much faster than the conventional version with a conditional branch:

    for (int i = 0; i < 1000; i++) {
        if (numbers[i] < 500) {
            small_numbers[smlen] = numbers[i];
            smlen += 1;
        }
    }

Been staring at this for a bit, but my brain is not working properly today: could someone please explain how these to loops compute the same value for small_numbers[smlen]?