Prime (From Prime95)

bool prost(int br) {
    if (br > 0 && br < 4) {
        return true;
    }
    else {
        for (int i = 2; i < 0xFFFF && i * i <= br; i = (i + 1) | 1) {
            if (br % i == 0) {
                return false;
            }
        }
        return true;
    }
}