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 <wes@softweyr.com>.
32 */
33
34 #include "namespace.h"
35 #include <sys/param.h>
36 #include <sys/sysctl.h>
37 #include <assert.h>
38 #include <pthread.h>
39 #include <stdbool.h>
40 #include <stdlib.h>
41 #include <syslog.h>
42 #include "un-namespace.h"
43
44 #include "libc_private.h"
45 #include "random.h"
46
47 /*
48 * Implement rand(3), the standard C PRNG API, using the non-standard but
49 * higher quality random(3) implementation and the same size 128-byte state
50 * LFSR as the random(3) default.
51 *
52 * It turns out there are portable applications that want a PRNG but are too
53 * lazy to use better-but-nonstandard interfaces like random(3), when
54 * available, and too lazy to import higher-quality and faster PRNGs into their
55 * codebase (such as any of SFC, JSF, 128-bit LCGs, PCG, or Splitmix64).
56 *
57 * Since we're stuck with rand(3) due to the C standard, we can at least have
58 * it produce a relatively good PRNG sequence using our existing random(3)
59 * LFSR. The random(3) design is not particularly fast nor compact, but it has
60 * the advantage of being the one already in the tree.
61 */
62 static struct __random_state *rand3_state;
63 static pthread_once_t rand3_state_once = PTHREAD_ONCE_INIT;
64
65 static void
initialize_rand3(void)66 initialize_rand3(void)
67 {
68 int error;
69
70 rand3_state = allocatestate(TYPE_3);
71 error = initstate_r(rand3_state, 1, rand3_state->rst_randtbl, BREAK_3);
72 assert(error == 0);
73 }
74
75 int
rand(void)76 rand(void)
77 {
78 _once(&rand3_state_once, initialize_rand3);
79 return ((int)random_r(rand3_state));
80 }
81
82 void
srand(unsigned seed)83 srand(unsigned seed)
84 {
85 _once(&rand3_state_once, initialize_rand3);
86 srandom_r(rand3_state, seed);
87 }
88
89 /*
90 * FreeBSD 12 and prior compatibility implementation of rand(3).
91 */
92 static int
do_rand(unsigned long * ctx)93 do_rand(unsigned long *ctx)
94 {
95 /*
96 * Compute x = (7^5 * x) mod (2^31 - 1)
97 * without overflowing 31 bits:
98 * (2^31 - 1) = 127773 * (7^5) + 2836
99 * From "Random number generators: good ones are hard to find",
100 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
101 * October 1988, p. 1195.
102 */
103 long hi, lo, x;
104
105 /* Transform to [1, 0x7ffffffe] range. */
106 x = (*ctx % 0x7ffffffe) + 1;
107 hi = x / 127773;
108 lo = x % 127773;
109 x = 16807 * lo - 2836 * hi;
110 if (x < 0)
111 x += 0x7fffffff;
112 /* Transform to [0, 0x7ffffffd] range. */
113 x--;
114 *ctx = x;
115 return (x);
116 }
117
118 /*
119 * Can't fix this garbage; too little state.
120 */
121 int
rand_r(unsigned * ctx)122 rand_r(unsigned *ctx)
123 {
124 u_long val;
125 int r;
126
127 val = *ctx;
128 r = do_rand(&val);
129 *ctx = (unsigned)val;
130 return (r);
131 }
132
133 static u_long next = 1;
134
135 int __rand_fbsd12(void);
136 int
__rand_fbsd12(void)137 __rand_fbsd12(void)
138 {
139 return (do_rand(&next));
140 }
141 __sym_compat(rand, __rand_fbsd12, FBSD_1.0);
142
143 void __srand_fbsd12(unsigned seed);
144 void
__srand_fbsd12(unsigned seed)145 __srand_fbsd12(unsigned seed)
146 {
147 next = seed;
148 }
149 __sym_compat(srand, __srand_fbsd12, FBSD_1.0);
150
151 void __sranddev_fbsd12(void);
152 void
__sranddev_fbsd12(void)153 __sranddev_fbsd12(void)
154 {
155 static bool warned = false;
156
157 if (!warned) {
158 syslog(LOG_DEBUG, "Deprecated function sranddev() called");
159 warned = true;
160 }
161 }
162 __sym_compat(sranddev, __sranddev_fbsd12, FBSD_1.0);
163