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  * 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  * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>.
  30  */
  31
  32 #if defined(LIBC_SCCS) && !defined(lint)
  33 static char sccsid[] = "@(#)rand.c      8.1 (Berkeley) 6/14/93";
  34 #endif /* LIBC_SCCS and not lint */
  35 #include <sys/cdefs.h>
  36 __FBSDID("$FreeBSD: src/lib/libc/stdlib/rand.c,v 1.17 2007/12/11 20:39:32 ache Exp $");
  37
  38 #include "namespace.h"
  39 #include <sys/time.h>          /* for sranddev() */
  40 #include <sys/types.h>
  41 #include <fcntl.h>             /* for sranddev() */
  42 #include <stdlib.h>
  43 #include <unistd.h>            /* for sranddev() */
  44 #include "un-namespace.h"
  45
  46 #ifdef TEST
  47 #include <stdio.h>
  48 #endif /* TEST */
  49
  50 static int
  51 do_rand(unsigned long *ctx)
  52 {
  53 #ifdef  USE_WEAK_SEEDING
  54 /*
  55  * Historic implementation compatibility.
  56  * The random sequences do not vary much with the seed,
  57  * even with overflowing.
  58  */
  59         return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
  60 #else   /* !USE_WEAK_SEEDING */
  61 /*
  62  * Compute x = (7^5 * x) mod (2^31 - 1)
  63  * without overflowing 31 bits:
  64  *      (2^31 - 1) = 127773 * (7^5) + 2836
  65  * From "Random number generators: good ones are hard to find",
  66  * Park and Miller, Communications of the ACM, vol. 31, no. 10,
  67  * October 1988, p. 1195.
  68  */
  69         long hi, lo, x;
  70
  71         /* Can't be initialized with 0, so use another value. */
  72         if (*ctx == 0)
  73                 *ctx = 123459876;
  74         hi = *ctx / 127773;
  75         lo = *ctx % 127773;
  76         x = 16807 * lo - 2836 * hi;
  77         if (x < 0)
  78                 x += 0x7fffffff;
  79         return ((*ctx = x) % ((u_long)RAND_MAX + 1));
  80 #endif  /* !USE_WEAK_SEEDING */
  81 }
  82
  83
  84 int
  85 rand_r(unsigned int *ctx)
  86 {
  87         u_long val = (u_long) *ctx;
  88         int r = do_rand(&val);
  89
  90         *ctx = (unsigned int) val;
  91         return (r);
  92 }
  93
  94
  95 static u_long next = 1;
  96
  97 int
  98 rand()
  99 {
 100         return (do_rand(&next));
 101 }
 102
 103 void
 104 srand(seed)
 105 u_int seed;
 106 {
 107         next = seed;
 108 }
 109
 110
 111 /*
 112  * sranddev:
 113  *
 114  * Many programs choose the seed value in a totally predictable manner.
 115  * This often causes problems.  We seed the generator using the much more
 116  * secure random(4) interface.
 117  */
 118 void
 119 sranddev()
 120 {
 121         int fd, done;
 122
 123         done = 0;
 124         fd = _open("/dev/random", O_RDONLY, 0);
 125         if (fd >= 0) {
 126                 if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next))
 127                         done = 1;
 128                 _close(fd);
 129         }
 130
 131         if (!done) {
 132                 struct timeval tv;
 133                 unsigned long junk;
 134
 135                 gettimeofday(&tv, NULL);
 136                 srand((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk);
 137         }
 138 }
 139
 140
 141 #ifdef TEST
 142
 143 main()
 144 {
 145     int i;
 146     unsigned myseed;
 147
 148     printf("seeding rand with 0x19610910: \n");
 149     srand(0x19610910);
 150
 151     printf("generating three pseudo-random numbers:\n");
 152     for (i = 0; i < 3; i++)
 153     {
 154         printf("next random number = %d\n", rand());
 155     }
 156
 157     printf("generating the same sequence with rand_r:\n");
 158     myseed = 0x19610910;
 159     for (i = 0; i < 3; i++)
 160     {
 161         printf("next random number = %d\n", rand_r(&myseed));
 162     }
 163
 164     return 0;
 165 }
 166
 167 #endif /* TEST */
 168