pub unsafe extern "C" fn mpi_gen_prime(
    X: *mut mpi,
    nbits: size_t,
    flags: c_int,
    f_rng: Option<unsafe extern "C" fn(arg1: *mut c_void, arg2: *mut c_uchar, arg3: size_t) -> c_int>,
    p_rng: *mut c_void
) -> c_int