1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1990, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the University nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 *
31 * Posix rand_r function added May 1999 by Wes Peters <[email protected]>.
32 */
33
34 #if defined(LIBC_SCCS) && !defined(lint)
35 static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93";
36 #endif /* LIBC_SCCS and not lint */
37 #include "namespace.h"
38 #include <sys/param.h>
39 #include <sys/sysctl.h>
40 #include <assert.h>
41 #include <pthread.h>
42 #include <stdbool.h>
43 #include <stdlib.h>
44 #include <syslog.h>
45 #include "un-namespace.h"
46
47 #include "libc_private.h"
48 #include "random.h"
49
50 /*
51 * Implement rand(3), the standard C PRNG API, using the non-standard but
52 * higher quality random(3) implementation and the same size 128-byte state
53 * LFSR as the random(3) default.
54 *
55 * It turns out there are portable applications that want a PRNG but are too
56 * lazy to use better-but-nonstandard interfaces like random(3), when
57 * available, and too lazy to import higher-quality and faster PRNGs into their
58 * codebase (such as any of SFC, JSF, 128-bit LCGs, PCG, or Splitmix64).
59 *
60 * Since we're stuck with rand(3) due to the C standard, we can at least have
61 * it produce a relatively good PRNG sequence using our existing random(3)
62 * LFSR. The random(3) design is not particularly fast nor compact, but it has
63 * the advantage of being the one already in the tree.
64 */
65 static struct __random_state *rand3_state;
66 static pthread_once_t rand3_state_once = PTHREAD_ONCE_INIT;
67
68 static void
initialize_rand3(void)69 initialize_rand3(void)
70 {
71 int error;
72
73 rand3_state = allocatestate(TYPE_3);
74 error = initstate_r(rand3_state, 1, rand3_state->rst_randtbl, BREAK_3);
75 assert(error == 0);
76 }
77
78 int
rand(void)79 rand(void)
80 {
81 _once(&rand3_state_once, initialize_rand3);
82 return ((int)random_r(rand3_state));
83 }
84
85 void
srand(unsigned seed)86 srand(unsigned seed)
87 {
88 _once(&rand3_state_once, initialize_rand3);
89 srandom_r(rand3_state, seed);
90 }
91
92 /*
93 * FreeBSD 12 and prior compatibility implementation of rand(3).
94 */
95 static int
do_rand(unsigned long * ctx)96 do_rand(unsigned long *ctx)
97 {
98 /*
99 * Compute x = (7^5 * x) mod (2^31 - 1)
100 * without overflowing 31 bits:
101 * (2^31 - 1) = 127773 * (7^5) + 2836
102 * From "Random number generators: good ones are hard to find",
103 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
104 * October 1988, p. 1195.
105 */
106 long hi, lo, x;
107
108 /* Transform to [1, 0x7ffffffe] range. */
109 x = (*ctx % 0x7ffffffe) + 1;
110 hi = x / 127773;
111 lo = x % 127773;
112 x = 16807 * lo - 2836 * hi;
113 if (x < 0)
114 x += 0x7fffffff;
115 /* Transform to [0, 0x7ffffffd] range. */
116 x--;
117 *ctx = x;
118 return (x);
119 }
120
121 /*
122 * Can't fix this garbage; too little state.
123 */
124 int
rand_r(unsigned * ctx)125 rand_r(unsigned *ctx)
126 {
127 u_long val;
128 int r;
129
130 val = *ctx;
131 r = do_rand(&val);
132 *ctx = (unsigned)val;
133 return (r);
134 }
135
136 static u_long next = 1;
137
138 int __rand_fbsd12(void);
139 int
__rand_fbsd12(void)140 __rand_fbsd12(void)
141 {
142 return (do_rand(&next));
143 }
144 __sym_compat(rand, __rand_fbsd12, FBSD_1.0);
145
146 void __srand_fbsd12(unsigned seed);
147 void
__srand_fbsd12(unsigned seed)148 __srand_fbsd12(unsigned seed)
149 {
150 next = seed;
151 }
152 __sym_compat(srand, __srand_fbsd12, FBSD_1.0);
153
154 void __sranddev_fbsd12(void);
155 void
__sranddev_fbsd12(void)156 __sranddev_fbsd12(void)
157 {
158 static bool warned = false;
159
160 if (!warned) {
161 syslog(LOG_DEBUG, "Deprecated function sranddev() called");
162 warned = true;
163 }
164 }
165 __sym_compat(sranddev, __sranddev_fbsd12, FBSD_1.0);
166