Function initid

freebsd/netinet6/ip6_id.c:183–225

* Initializes the seed and chooses a suitable generator. Also toggles * the msb flag. The msb flag is used to generate two distinct * cycles of random numbers and thus avoiding reuse of ids. * * This function is called from id_randomid() when needed, an * application does not have to worry about it. */

 * application does not have to worry about it.
 */
static void
initid(struct randomtab *p)
{
	u_int32_t j, i;
	int noprime = 1;

	p->ru_x = arc4random() % p->ru_m;

	/* (bits - 1) bits of random seed */
	p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
	p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));

	/* Determine the LCG we use */
	p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
	p->ru_a = pmod(p->ru_agen,
	    (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
	while (p->ru_b % 3 == 0)
		p->ru_b += 2;

	j = arc4random() % p->ru_n;

	/*
	 * Do a fast gcd(j, RU_N - 1), so we can find a j with
	 * gcd(j, RU_N - 1) == 1, giving a new generator for
	 * RU_GEN^j mod RU_N
	 */
	while (noprime) {
		for (i = 0; p->pfacts[i] > 0; i++)
			if (j % p->pfacts[i] == 0)
				break;

		if (p->pfacts[i] == 0)
			noprime = 0;
		else
			j = (j + 1) % p->ru_n;
	}

	p->ru_g = pmod(p->ru_gen, j, p->ru_n);
	p->ru_counter = 0;

	p->ru_reseed = time_uptime + p->ru_out;
	p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
}

static u_int32_t
randomid(struct randomtab *p)