stdlib/FreeBSD/rand.c

   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 #if defined(LIBC_SCCS) && !defined(lint)
  37 static char sccsid[] = "@(#)rand.c      8.1 (Berkeley) 6/14/93";
  38 #endif /* LIBC_SCCS and not lint */
  39 #include <sys/cdefs.h>
  40 __FBSDID("$FreeBSD: src/lib/libc/stdlib/rand.c,v 1.15 2003/02/17 03:52:35 ache Exp $");
  41
  42 #include "namespace.h"
  43 #include <sys/time.h>          /* for sranddev() */
  44 #include <sys/types.h>
  45 #include <fcntl.h>             /* for sranddev() */
  46 #include <stdlib.h>
  47 #include <unistd.h>            /* for sranddev() */
  48 #include "un-namespace.h"
  49
  50 #ifdef TEST
  51 #include <stdio.h>
  52 #endif /* TEST */
  53
  54 static int
  55 do_rand(unsigned long *ctx)
  56 {
  57 #ifdef  USE_WEAK_SEEDING
  58 /*
  59  * Historic implementation compatibility.
  60  * The random sequences do not vary much with the seed,
  61  * even with overflowing.
  62  */
  63         return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
  64 #else   /* !USE_WEAK_SEEDING */
  65 /*
  66  * Compute x = (7^5 * x) mod (2^31 - 1)
  67  * wihout overflowing 31 bits:
  68  *      (2^31 - 1) = 127773 * (7^5) + 2836
  69  * From "Random number generators: good ones are hard to find",
  70  * Park and Miller, Communications of the ACM, vol. 31, no. 10,
  71  * October 1988, p. 1195.
  72  */
  73         long hi, lo, x;
  74
  75         /* Can't be initialized with 0, so use another value. */
  76         if (*ctx == 0)
  77                 *ctx = 123459876;
  78         hi = *ctx / 127773;
  79         lo = *ctx % 127773;
  80         x = 16807 * lo - 2836 * hi;
  81         if (x < 0)
  82                 x += 0x7fffffff;
  83         return ((*ctx = x) % ((u_long)RAND_MAX + 1));
  84 #endif  /* !USE_WEAK_SEEDING */
  85 }
  86
  87
  88 int
  89 rand_r(unsigned int *ctx)
  90 {
  91         u_long val = (u_long) *ctx;
  92         int r = do_rand(&val);
  93
  94         *ctx = (unsigned int) val;
  95         return (r);
  96 }
  97
  98
  99 static u_long next = 1;
 100
 101 int
 102 rand()
 103 {
 104         return (do_rand(&next));
 105 }
 106
 107 void
 108 srand(seed)
 109 u_int seed;
 110 {
 111         next = seed;
 112 }
 113
 114
 115 /*
 116  * sranddev:
 117  *
 118  * Many programs choose the seed value in a totally predictable manner.
 119  * This often causes problems.  We seed the generator using the much more
 120  * secure random(4) interface.
 121  */
 122 void
 123 sranddev()
 124 {
 125         int fd, done;
 126
 127         done = 0;
 128         fd = _open("/dev/random", O_RDONLY, 0);
 129         if (fd >= 0) {
 130                 if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next))
 131                         done = 1;
 132                 _close(fd);
 133         }
 134
 135         if (!done) {
 136                 struct timeval tv;
 137                 unsigned long junk;
 138
 139                 gettimeofday(&tv, NULL);
 140                 srand((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk);
 141         }
 142 }
 143
 144
 145 #ifdef TEST
 146
 147 main()
 148 {
 149     int i;
 150     unsigned myseed;
 151
 152     printf("seeding rand with 0x19610910: \n");
 153     srand(0x19610910);
 154
 155     printf("generating three pseudo-random numbers:\n");
 156     for (i = 0; i < 3; i++)
 157     {
 158         printf("next random number = %d\n", rand());
 159     }
 160
 161     printf("generating the same sequence with rand_r:\n");
 162     myseed = 0x19610910;
 163     for (i = 0; i < 3; i++)
 164     {
 165         printf("next random number = %d\n", rand_r(&myseed));
 166     }
 167
 168     return 0;
 169 }
 170
 171 #endif /* TEST */
 172