1/*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22/*
23 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
24 * Use is subject to license terms.
25 */
26
27/*	Copyright (c) 1988 AT&T	*/
28/*	  All Rights Reserved  	*/
29
30/*
31 * University Copyright- Copyright (c) 1982, 1986, 1988
32 * The Regents of the University of California
33 * All Rights Reserved
34 *
35 * University Acknowledgment- Portions of this document are derived from
36 * software developed by the University of California, Berkeley, and its
37 * contributors.
38 */
39
40#pragma ident	"%Z%%M%	%I%	%E% SMI"
41
42#include "lint.h"
43#include "thr_uberdata.h"
44#include <stdlib.h>
45#include <atomic.h>
46
47/*
48 * We need atomic_cas_uint() protection because a multithreaded process
49 * may be calling rand() from different threads and because multiple
50 * threads may be calling rand_r() using a pointer to the same seed.
51 */
52
53static uint_t rand_seed = 1;
54
55#define	NEXT_SEED(s)	((s) * 1103515245 + 12345)
56#define	NEXT_VALUE(s)	(((s) >> 16) & 0x7fff)
57
58static int
59rand_mt(uint_t *seed)
60{
61	uint_t old_seed;
62	uint_t new_seed;
63
64	for (;;) {
65		/* force reload on every iteration */
66		old_seed = *(volatile uint_t *)seed;
67		new_seed = NEXT_SEED(old_seed);
68		if (atomic_cas_uint(seed, old_seed, new_seed) == old_seed)
69			return (NEXT_VALUE(new_seed));
70		SMT_PAUSE();
71	}
72}
73
74int
75rand_r(uint_t *seed)
76{
77	if (curthread->ul_uberdata->uberflags.uf_mt)
78		return (rand_mt(seed));
79	return (NEXT_VALUE(*seed = NEXT_SEED(*seed)));
80}
81
82void
83srand(uint_t seed)
84{
85	rand_seed = seed;
86}
87
88int
89rand(void)
90{
91	return (rand_r(&rand_seed));
92}
93