Annotation of sys/lib/libkern/random.c, Revision 1.1.1.1
1.1 nbrk 1: /* $OpenBSD: random.c,v 1.7 2004/08/07 00:38:33 deraadt Exp $ */
2: /* $NetBSD: random.c,v 1.2 1994/10/26 06:42:42 cgd Exp $ */
3:
4: /*-
5: * Copyright (c) 1992, 1993
6: * The Regents of the University of California. All rights reserved.
7: *
8: * Redistribution and use in source and binary forms, with or without
9: * modification, are permitted provided that the following conditions
10: * are met:
11: * 1. Redistributions of source code must retain the above copyright
12: * notice, this list of conditions and the following disclaimer.
13: * 2. Redistributions in binary form must reproduce the above copyright
14: * notice, this list of conditions and the following disclaimer in the
15: * documentation and/or other materials provided with the distribution.
16: * 3. Neither the name of the University nor the names of its contributors
17: * may be used to endorse or promote products derived from this software
18: * without specific prior written permission.
19: *
20: * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23: * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30: * SUCH DAMAGE.
31: *
32: * @(#)random.c 8.1 (Berkeley) 6/10/93
33: */
34:
35: #include <sys/types.h>
36:
37: #include <lib/libkern/libkern.h>
38:
39: /*
40: * Pseudo-random number generator for randomizing the profiling clock,
41: * and whatever else we might use it for. The result is uniform on
42: * [0, 2^31 - 1].
43: */
44: u_long _randseed = 1;
45:
46: u_long
47: random(void)
48: {
49: long x, hi, lo, t;
50:
51: /*
52: * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
53: * From "Random number generators: good ones are hard to find",
54: * Park and Miller, Communications of the ACM, vol. 31, no. 10,
55: * October 1988, p. 1195.
56: */
57: x = _randseed;
58: hi = x / 127773;
59: lo = x % 127773;
60: t = 16807 * lo - 2836 * hi;
61: if (t <= 0)
62: t += 0x7fffffff;
63: _randseed = t;
64: return (t);
65: }
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