FreeBSD/Linux Kernel Cross Reference
sys/libkern/random.c
1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1992, 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 * @(#)random.c 8.1 (Berkeley) 6/10/93
32 */
33
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
36
37 #include <sys/libkern.h>
38
39 #define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */
40
41 static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
42
43 void
44 srandom(u_long seed)
45 {
46 int i;
47
48 randseed = seed;
49 for (i = 0; i < NSHUFF; i++)
50 (void)random();
51 }
52
53 /*
54 * Pseudo-random number generator for perturbing the profiling clock,
55 * and whatever else we might use it for. The result is uniform on
56 * [0, 2^31 - 1].
57 */
58 u_long
59 random()
60 {
61 long x, hi, lo, t;
62
63 /*
64 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
65 * From "Random number generators: good ones are hard to find",
66 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
67 * October 1988, p. 1195.
68 */
69 /* Can't be initialized with 0, so use another value. */
70 if ((x = randseed) == 0)
71 x = 123459876;
72 hi = x / 127773;
73 lo = x % 127773;
74 t = 16807 * lo - 2836 * hi;
75 if (t < 0)
76 t += 0x7fffffff;
77 randseed = t;
78 return (t);
79 }
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