Annotation of prex/usr/lib/libc/stdlib/random.c, Revision 1.1.1.1
1.1 nbrk 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: #include <sys/types.h>
34: #include <stdlib.h>
35:
36: #define NSHUFF 50 /* to drop some "seed -> 1st value" linearity */
37:
38: static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
39:
40: void
41: srandom(seed)
42: u_long seed;
43: {
44: int i;
45:
46: randseed = seed;
47: for (i = 0; i < NSHUFF; i++)
48: (void)random();
49: }
50:
51: /*
52: * Pseudo-random number generator for randomizing the profiling clock,
53: * and whatever else we might use it for. The result is uniform on
54: * [0, 2^31 - 1].
55: */
56: long
57: random()
58: {
59: long x, hi, lo, t;
60:
61: /*
62: * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
63: * From "Random number generators: good ones are hard to find",
64: * Park and Miller, Communications of the ACM, vol. 31, no. 10,
65: * October 1988, p. 1195.
66: */
67: /* Can't be initialized with 0, so use another value. */
68: if ((x = randseed) == 0)
69: x = 123459876;
70: hi = x / 127773;
71: lo = x % 127773;
72: t = 16807 * lo - 2836 * hi;
73: if (t < 0)
74: t += 0x7fffffff;
75: randseed = t;
76: return (t);
77: }
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