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