Function arc4rand

freebsd/libkern/arc4random.c:188–237

* MPSAFE */

 * MPSAFE
 */
void
arc4rand(void *ptr, u_int len, int reseed)
{
	struct chacha20_s *chacha20;
	struct timeval tv;
	u_int length;
	u_int8_t *p;

#ifdef RANDOM_FENESTRASX
	if (__predict_false(reseed))
#else
	if (__predict_false(reseed ||
	    (arc4rand_iniseed_state == ARC4_ENTR_HAVE &&
	    atomic_cmpset_int(&arc4rand_iniseed_state, ARC4_ENTR_HAVE, ARC4_ENTR_SEED))))
#endif
		CHACHA20_FOREACH(chacha20)
			chacha20_randomstir(chacha20);

	getmicrouptime(&tv);
	chacha20 = &chacha20inst[curcpu];
	/* We may get unlucky and be migrated off this CPU, but that is expected to be infrequent */
	if ((chacha20->numbytes > CHACHA20_RESEED_BYTES) || (tv.tv_sec > chacha20->t_reseed))
		chacha20_randomstir(chacha20);

	mtx_lock(&chacha20->mtx);
#ifdef RANDOM_FENESTRASX
	if (__predict_false(
	    atomic_load_acq_64(&fxrng_root_generation) != chacha20->seed_version
	    )) {
		mtx_unlock(&chacha20->mtx);
		chacha20_randomstir(chacha20);
		mtx_lock(&chacha20->mtx);
	}
#endif

	p = ptr;
	while (len) {
		length = MIN(CHACHA20_BUFFER_SIZE, len);
		chacha_encrypt_bytes(&chacha20->ctx, chacha20->m_buffer, p, length);
		p += length;
		len -= length;
		chacha20->numbytes += length;
		if (chacha20->numbytes > CHACHA20_RESEED_BYTES) {
			mtx_unlock(&chacha20->mtx);
			chacha20_randomstir(chacha20);
			mtx_lock(&chacha20->mtx);
		}
	}
	mtx_unlock(&chacha20->mtx);
}

uint32_t
arc4random(void)