Say I have some function

unsigned int my_random_value(unsigned int a);

that returns a value in the range 0, 1, …, a – 1. I want to assert GCC that the return value will be in this range, but I don’t know how to do it nicely. By wrapping this function, GCC could be noticed of this via

unsigned int my_random_value(unsigned int a);

static inline
unsigned int my_random_value_wrapper(unsigned int a)
{
    unsigned int ret = my_random_value(a);

    if (ret >= a)
        __builtin_unreachable();

    return ret;
}

but that will be quite large in a header file, and will not let me use my_random_value to directly access this function. Is there a better way to do it, perhaps through attributes?