ru_m
p->ru_x = arc4random() % p->ru_m;
(arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
p->ru_x = (u_int32_t)(((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m);