Function rte_rand_max

dpdk/lib/eal/common/rte_random.c:144–181

}

uint64_t
rte_rand_max(uint64_t upper_bound)
{
	struct rte_rand_state *state;
	uint8_t ones;
	uint8_t leading_zeros;
	uint64_t mask = ~((uint64_t)0);
	uint64_t res;

	if (unlikely(upper_bound < 2))
		return 0;

	state = __rte_rand_get_state();

	ones = rte_popcount64(upper_bound);

	/* Handle power-of-2 upper_bound as a special case, since it
	 * has no bias issues.
	 */
	if (unlikely(ones == 1))
		return __rte_rand_lfsr258(state) & (upper_bound - 1);

	/* The approach to avoiding bias is to create a mask that
	 * stretches beyond the request value range, and up to the
	 * next power-of-2. In case the masked generated random value
	 * is equal to or greater than the upper bound, just discard
	 * the value and generate a new one.
	 */

	leading_zeros = rte_clz64(upper_bound);
	mask >>= leading_zeros;

	do {
		res = __rte_rand_lfsr258(state) & mask;
	} while (unlikely(res >= upper_bound));

	return res;
}

double
rte_drand(void)