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  * 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  * $FreeBSD: src/lib/libc/stdlib/rand.c,v 1.2.2.1 2001/03/05 11:33:57 obrien Exp $
  36  */
  37
  38 #if defined(LIBC_SCCS) && !defined(lint)
  39 static char sccsid[] = "@(#)rand.c      8.1 (Berkeley) 6/14/93";
  40 #endif /* LIBC_SCCS and not lint */
  41
  42 #include <sys/types.h>
  43 #include <stdlib.h>
  44
  45 #ifdef TEST
  46 #include <stdio.h>
  47 #endif /* TEST */
  48
  49 static int
  50 do_rand(unsigned long *ctx)
  51 {
  52         return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1));
  53 }
  54
  55
  56 int
  57 rand_r(unsigned int *ctx)
  58 {
  59         u_long val = (u_long) *ctx;
  60         *ctx = do_rand(&val);
  61         return (int) *ctx;
  62 }
  63
  64
  65 static u_long next = 1;
  66
  67 int
  68 rand()
  69 {
  70         return do_rand(&next);
  71 }
  72
  73 void
  74 srand(seed)
  75 u_int seed;
  76 {
  77         next = seed;
  78 }
  79
  80 #ifdef TEST
  81
  82 main()
  83 {
  84     int i;
  85     unsigned myseed;
  86
  87     printf("seeding rand with 0x19610910: \n");
  88     srand(0x19610910);
  89
  90     printf("generating three pseudo-random numbers:\n");
  91     for (i = 0; i < 3; i++)
  92     {
  93         printf("next random number = %d\n", rand());
  94     }
  95
  96     printf("generating the same sequence with rand_r:\n");
  97     myseed = 0x19610910;
  98     for (i = 0; i < 3; i++)
  99     {
 100         printf("next random number = %d\n", rand_r(&myseed));
 101     }
 102
 103     return 0;
 104 }
 105
 106 #endif /* TEST */
 107