FreeBSD/Linux Kernel Cross Reference
sys/libkern/random.c
1 /*-
2 * Copyright (c) 1992, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 * This product includes software developed by the University of
16 * California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 *
33 * @(#)random.c 8.1 (Berkeley) 6/10/93
34 * $FreeBSD: releng/5.1/sys/libkern/random.c 110422 2003-02-05 21:28:52Z ache $
35 */
36
37 #include <sys/libkern.h>
38
39 #define NSHUFF 100 /* to drop part of seed -> 1st value correlation */
40
41 static u_long randseed = 892053144; /* after srandom(1), NSHUFF counted */
42
43 void
44 srandom(seed)
45 u_long seed;
46 {
47 int i;
48
49 randseed = seed;
50 for (i = 0; i < NSHUFF; i++)
51 (void)random();
52 }
53
54 /*
55 * Pseudo-random number generator for randomizing the profiling clock,
56 * and whatever else we might use it for. The result is uniform on
57 * [0, 2^31 - 1].
58 */
59 u_long
60 random()
61 {
62 register long x, hi, lo, t;
63
64 /*
65 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
66 * From "Random number generators: good ones are hard to find",
67 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
68 * October 1988, p. 1195.
69 */
70 /* Can't be initialized with 0, so use another value. */
71 if ((x = randseed) == 0)
72 x = 123459876;
73 hi = x / 127773;
74 lo = x % 127773;
75 t = 16807 * lo - 2836 * hi;
76 if (t < 0)
77 t += 0x7fffffff;
78 randseed = t;
79 return (t);
80 }
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