C++ prandom_u32函数代码示例

static void double_bit_error_data(void *error_data, void *correct_data,
				size_t size)
{
	unsigned int offset[2];

	offset[0] = prandom_u32() % (size * BITS_PER_BYTE);
	do {
		offset[1] = prandom_u32() % (size * BITS_PER_BYTE);
	} while (offset[0] == offset[1]);

	memcpy(error_data, correct_data, size);

	__change_bit_le(offset[0], error_data);
	__change_bit_le(offset[1], error_data);
}

static unsigned int random_ecc_bit(size_t size)
{
	unsigned int offset = prandom_u32() % (3 * BITS_PER_BYTE);

	if (size == 256) {
		/*
		 * Don't inject a bit error into the insignificant bits (16th
		 * and 17th bit) in ECC code for 256 byte data block
		 */
		while (offset == 16 || offset == 17)
			offset = prandom_u32() % (3 * BITS_PER_BYTE);
	}

	return offset;
}

struct bpf_binary_header *bpf_alloc_binary(unsigned int proglen,
						  u8 **image_ptr)
{
	unsigned int sz, hole;
	struct bpf_binary_header *header;

	/* Most of BPF filters are really small,
	 * but if some of them fill a page, allow at least
	 * 128 extra bytes to insert a random section of int3
	 */
	sz = round_up(proglen + sizeof(*header) + 128, PAGE_SIZE);
	header = module_alloc(sz);
	if (!header)
		return NULL;

	memset(header, 0xcc, sz); /* fill whole space with int3 instructions */

	header->pages = sz / PAGE_SIZE;
	hole = sz - (proglen + sizeof(*header));

	/* insert a random number of int3 instructions before BPF code */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,10,0)
	*image_ptr = &header->image[prandom_u32() % hole];
#else
	*image_ptr = &header->image[32 % hole];
#endif
	return header;
}

static int gact_net_rand(struct tcf_gact *gact)
{
	smp_rmb(); /* coupled with smp_wmb() in tcf_gact_init() */
	if (prandom_u32() % gact->tcfg_pval)
		return gact->tcf_action;
	return gact->tcfg_paction;
}

static void yam_arbitrate(struct net_device *dev)
{
	struct yam_port *yp = netdev_priv(dev);

	if (yp->magic != YAM_MAGIC || yp->tx_state != TX_OFF ||
	    skb_queue_empty(&yp->send_queue))
		return;
	/* tx_state is TX_OFF and there is data to send */

	if (yp->dupmode) {
		/* Full duplex mode, don't wait */
		yam_start_tx(dev, yp);
		return;
	}
	if (yp->dcd) {
		/* DCD on, wait slotime ... */
		yp->slotcnt = yp->slot / 10;
		return;
	}
	/* Is slottime passed ? */
	if ((--yp->slotcnt) > 0)
		return;

	yp->slotcnt = yp->slot / 10;

	/* is random > persist ? */
	if ((prandom_u32() % 256) > yp->pers)
		return;

	yam_start_tx(dev, yp);
}

int __sbitmap_queue_get(struct sbitmap_queue *sbq)
{
	unsigned int hint, depth;
	int nr;

	hint = this_cpu_read(*sbq->alloc_hint);
	depth = READ_ONCE(sbq->sb.depth);
	if (unlikely(hint >= depth)) {
		hint = depth ? prandom_u32() % depth : 0;
		this_cpu_write(*sbq->alloc_hint, hint);
	}
	nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);

	if (nr == -1) {
		/* If the map is full, a hint won't do us much good. */
		this_cpu_write(*sbq->alloc_hint, 0);
	} else if (nr == hint || unlikely(sbq->round_robin)) {
		/* Only update the hint if we used it. */
		hint = nr + 1;
		if (hint >= depth - 1)
			hint = 0;
		this_cpu_write(*sbq->alloc_hint, hint);
	}

	return nr;
}

static int
qtnf_mgmt_tx(struct wiphy *wiphy, struct wireless_dev *wdev,
	     struct cfg80211_mgmt_tx_params *params, u64 *cookie)
{
	struct qtnf_vif *vif = qtnf_netdev_get_priv(wdev->netdev);
	const struct ieee80211_mgmt *mgmt_frame = (void *)params->buf;
	u32 short_cookie = prandom_u32();
	u16 flags = 0;

	*cookie = short_cookie;

	if (params->offchan)
		flags |= QLINK_MGMT_FRAME_TX_FLAG_OFFCHAN;

	if (params->no_cck)
		flags |= QLINK_MGMT_FRAME_TX_FLAG_NO_CCK;

	if (params->dont_wait_for_ack)
		flags |= QLINK_MGMT_FRAME_TX_FLAG_ACK_NOWAIT;

	pr_debug("%s freq:%u; FC:%.4X; DA:%pM; len:%zu; C:%.8X; FL:%.4X\n",
		 wdev->netdev->name, params->chan->center_freq,
		 le16_to_cpu(mgmt_frame->frame_control), mgmt_frame->da,
		 params->len, short_cookie, flags);

	return qtnf_cmd_send_mgmt_frame(vif, short_cookie, flags,
					params->chan->center_freq,
					params->buf, params->len);
}

static int do_operation(void)
{
	if (prandom_u32() & 1)
		return do_read();
	else
		return do_write();
}

/*
 * Pick a new monitor at random and set cur_mon.  If we are repicking
 * (i.e. cur_mon is already set), be sure to pick a different one.
 */
static void pick_new_mon(struct ceph_mon_client *monc)
{
	int old_mon = monc->cur_mon;

	BUG_ON(monc->monmap->num_mon < 1);

	if (monc->monmap->num_mon == 1) {
		monc->cur_mon = 0;
	} else {
		int max = monc->monmap->num_mon;
		int o = -1;
		int n;

		if (monc->cur_mon >= 0) {
			if (monc->cur_mon < monc->monmap->num_mon)
				o = monc->cur_mon;
			if (o >= 0)
				max--;
		}

		n = prandom_u32() % max;
		if (o >= 0 && n >= o)
			n++;

		monc->cur_mon = n;
	}

	dout("%s mon%d -> mon%d out of %d mons\n", __func__, old_mon,
	     monc->cur_mon, monc->monmap->num_mon);
}

static struct bpf_binary_header *bpf_alloc_binary(unsigned int proglen,
						  u8 **image_ptr)
{
	unsigned int sz, hole;
	struct bpf_binary_header *header;

	/* Most of BPF filters are really small,
	 * but if some of them fill a page, allow at least
	 * 128 extra bytes to insert a random section of int3
	 */
	sz = round_up(proglen + sizeof(*header) + 128, PAGE_SIZE);
/*
	header = module_alloc(sz);
	if (!header)
		return NULL;
*/
	header = mmap(NULL, sz, PROT_READ|PROT_WRITE|PROT_EXEC,
                      MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
        if ((void *)header == MAP_FAILED) {
		perror("bpf_jit_comp.c: mmap");
		exit(EXIT_FAILURE);
	}

	memset(header, 0xcc, sz); /* fill whole space with int3 instructions */

	header->pages = sz / PAGE_SIZE;
	hole = min(sz - (proglen + sizeof(*header)), PAGE_SIZE - sizeof(*header));

	/* insert a random number of int3 instructions before BPF code */
#define prandom_u32() 0
	*image_ptr = &header->image[prandom_u32() % hole];
#undef prandom_u32
	return header;
}

/*
 * choose a random mds that is "up" (i.e. has a state > 0), or -1.
 */
int ceph_mdsmap_get_random_mds(struct ceph_mdsmap *m)
{
	int n = 0;
	int i;

	/* special case for one mds */
	if (1 == m->m_max_mds && m->m_info[0].state > 0)
		return 0;

	/* count */
	for (i = 0; i < m->m_max_mds; i++)
		if (m->m_info[i].state > 0)
			n++;
	if (n == 0)
		return -1;

	/* pick */
	n = prandom_u32() % n;
	i = 0;
	for (i = 0; n > 0; i++, n--)
		while (m->m_info[i].state <= 0)
			i++;

	return i;
}

void nf_nat_l4proto_unique_tuple(const struct nf_nat_l3proto *l3proto,
				 struct nf_conntrack_tuple *tuple,
				 const struct nf_nat_range *range,
				 enum nf_nat_manip_type maniptype,
				 const struct nf_conn *ct,
				 u16 *rover)
{
	unsigned int range_size, min, i;
	__be16 *portptr;
	u_int16_t off;

	if (maniptype == NF_NAT_MANIP_SRC)
		portptr = &tuple->src.u.all;
	else
		portptr = &tuple->dst.u.all;

	/* If no range specified... */
	if (!(range->flags & NF_NAT_RANGE_PROTO_SPECIFIED)) {
		/* If it's dst rewrite, can't change port */
		if (maniptype == NF_NAT_MANIP_DST)
			return;

		if (ntohs(*portptr) < 1024) {
			/* Loose convention: >> 512 is credential passing */
			if (ntohs(*portptr) < 512) {
				min = 1;
				range_size = 511 - min + 1;
			} else {
				min = 600;
				range_size = 1023 - min + 1;
			}
		} else {
			min = 1024;
			range_size = 65535 - 1024 + 1;
		}
	} else {
		min = ntohs(range->min_proto.all);
		range_size = ntohs(range->max_proto.all) - min + 1;
	}

	if (range->flags & NF_NAT_RANGE_PROTO_RANDOM) {
		off = l3proto->secure_port(tuple, maniptype == NF_NAT_MANIP_SRC
						  ? tuple->dst.u.all
						  : tuple->src.u.all);
	} else if (range->flags & NF_NAT_RANGE_PROTO_RANDOM_FULLY) {
		off = prandom_u32();
	} else {
		off = *rover;
	}

	for (i = 0; ; ++off) {
		*portptr = htons(min + off % range_size);
		if (++i != range_size && nf_nat_used_tuple(tuple, ct))
			continue;
		if (!(range->flags & NF_NAT_RANGE_PROTO_RANDOM_ALL))
			*rover = off;
		return;
	}
}

static int bitfliptest_do_operation(void)
{
	if (prandom_u32() & 1) {
		return bitfliptest_do_read();
	} else {
		return bitfliptest_do_write();
	}
}

static void single_bit_error_data(void *error_data, void *correct_data,
				size_t size)
{
	unsigned int offset = prandom_u32() % (size * BITS_PER_BYTE);

	memcpy(error_data, correct_data, size);
	__change_bit_le(offset, error_data);
}

static int rand_offs(void)
{
	unsigned int offs;

	offs = prandom_u32();
	offs %= bufsize;
	return offs;
}