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 * 4. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 *
29 * @(#)random.c 8.1 (Berkeley) 6/10/93
30 */
31
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD: src/sys/libkern/random.c,v 1.13 2004/04/07 20:46:10 imp Exp $");
34
35 #include <sys/libkern.h>
36
37 #define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */
38
39 static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
40
41 void
42 srandom(seed)
43 u_long seed;
44 {
45 int i;
46
47 randseed = seed;
48 for (i = 0; i < NSHUFF; i++)
49 (void)random();
50 }
51
52 /*
53 * Pseudo-random number generator for randomizing the profiling clock,
54 * and whatever else we might use it for. The result is uniform on
55 * [0, 2^31 - 1].
56 */
57 u_long
58 random()
59 {
60 register long x, hi, lo, t;
61
62 /*
63 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
64 * From "Random number generators: good ones are hard to find",
65 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
66 * October 1988, p. 1195.
67 */
68 /* Can't be initialized with 0, so use another value. */
69 if ((x = randseed) == 0)
70 x = 123459876;
71 hi = x / 127773;
72 lo = x % 127773;
73 t = 16807 * lo - 2836 * hi;
74 if (t < 0)
75 t += 0x7fffffff;
76 randseed = t;
77 return (t);
78 }
79
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