StdLib/LibC/StdLib/Rand.c

   1 /*-
   2  * Portions Copyright (c) 2010, Intel Corporation. All rights reserved.<BR>
   3  * Copyright (c) 1990, 1993
   4  *  The Regents of the University of California.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 4. Neither the name of the University nor the names of its contributors
  15  *    may be used to endorse or promote products derived from this software
  16  *    without specific prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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  23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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  30  */
  31 //__FBSDID("$FreeBSD: src/lib/libc/stdlib/rand.c,v 1.17.2.1.2.1 2009/10/25 01:10:29 kensmith Exp $");
  32 #include  <LibConfig.h>
  33
  34 #include  <stdlib.h>
  35
  36 static UINT32 next = 1;
  37
  38 /** Compute a pseudo-random number.
  39   *
  40   * Compute x = (7^5 * x) mod (2^31 - 1)
  41   * without overflowing 31 bits:
  42   *      (2^31 - 1) = 127773 * (7^5) + 2836
  43   * From "Random number generators: good ones are hard to find",
  44   * Park and Miller, Communications of the ACM, vol. 31, no. 10,
  45   * October 1988, p. 1195.
  46 **/
  47 int
  48 rand()
  49 {
  50   INT32 hi, lo, x;
  51
  52   /* Can't be initialized with 0, so use another value. */
  53   if (next == 0)
  54     next = 123459876;
  55   hi = next / 127773;
  56   lo = next % 127773;
  57   x = 16807 * lo - 2836 * hi;
  58   if (x < 0)
  59     x += 0x7fffffff;
  60   return ((next = x) % ((UINT32)RAND_MAX + 1));
  61 }
  62
  63 void
  64 srand(unsigned int seed)
  65 {
  66   next = (UINT32)seed;
  67 }