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 #include "lint.h"
41 #include "thr_uberdata.h"
42 #include <stdlib.h>
43 #include <atomic.h>
44
45 /*
46 * We need atomic_cas_uint() protection because a multithreaded process
47 * may be calling rand() from different threads and because multiple
48 * threads may be calling rand_r() using a pointer to the same seed.
49 */
50
51 static uint_t rand_seed = 1;
52
53 #define NEXT_SEED(s) ((s) * 1103515245 + 12345)
54 #define NEXT_VALUE(s) (((s) >> 16) & 0x7fff)
55
56 static int
rand_mt(uint_t * seed)57 rand_mt(uint_t *seed)
58 {
59 uint_t old_seed;
60 uint_t new_seed;
61
62 for (;;) {
63 /* force reload on every iteration */
64 old_seed = *(volatile uint_t *)seed;
65 new_seed = NEXT_SEED(old_seed);
66 if (atomic_cas_uint(seed, old_seed, new_seed) == old_seed)
67 return (NEXT_VALUE(new_seed));
68 SMT_PAUSE();
69 }
70 }
71
72 int
rand_r(uint_t * seed)73 rand_r(uint_t *seed)
74 {
75 if (curthread->ul_uberdata->uberflags.uf_mt)
76 return (rand_mt(seed));
77 return (NEXT_VALUE(*seed = NEXT_SEED(*seed)));
78 }
79
80 void
srand(uint_t seed)81 srand(uint_t seed)
82 {
83 rand_seed = seed;
84 }
85
86 int
rand(void)87 rand(void)
88 {
89 return (rand_r(&rand_seed));
90 }
91