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rand.c (3130B)
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1 /*-
2 * Copyright (c) 1990, 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 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
34 */
35
36 #include <sys/types.h>
37 #include <stdlib.h>
38
39 typedef unsigned long u_long;
40 typedef unsigned int u_int;
41
42 static int
43 do_rand(unsigned long *ctx)
44 {
45 #ifdef USE_WEAK_SEEDING
46 /*
47 * Historic implementation compatibility.
48 * The random sequences do not vary much with the seed,
49 * even with overflowing.
50 */
51 return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
52 #else /* !USE_WEAK_SEEDING */
53 /*
54 * Compute x = (7^5 * x) mod (2^31 - 1)
55 * wihout overflowing 31 bits:
56 * (2^31 - 1) = 127773 * (7^5) + 2836
57 * From "Random number generators: good ones are hard to find",
58 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
59 * October 1988, p. 1195.
60 */
61 long hi, lo, x;
62
63 /* Can't be initialized with 0, so use another value. */
64 if (*ctx == 0)
65 *ctx = 123459876;
66 hi = *ctx / 127773;
67 lo = *ctx % 127773;
68 x = 16807 * lo - 2836 * hi;
69 if (x < 0)
70 x += 0x7fffffff;
71 return ((*ctx = x) % ((u_long)RAND_MAX + 1));
72 #endif /* !USE_WEAK_SEEDING */
73 }
74
75
76 int
77 rand_r(unsigned int *ctx)
78 {
79 u_long val = (u_long) *ctx;
80 int r = do_rand(&val);
81
82 *ctx = (unsigned int) val;
83 return (r);
84 }
85
86 static u_long next = 1;
87
88 int
89 rand()
90 {
91 return (do_rand(&next));
92 }
93
94 void
95 srand(seed)
96 u_int seed;
97 {
98 next = seed;
99 }
100