sys/libkern/random.c

   1 /*-
   2  * Copyright (c) 1992, 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. 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  *      @(#)random.c    8.1 (Berkeley) 6/10/93
  30  * $FreeBSD: src/sys/libkern/random.c,v 1.7 1999/08/28 00:46:36 peter Exp $
  31  * $DragonFly: src/sys/libkern/random.c,v 1.6 2006/09/03 18:52:29 dillon Exp $
  32  */
  33
  34 #include <sys/libkern.h>
  35
  36 static u_long randseed = 1;
  37
  38 void
  39 skrandom(u_long seed)
  40 {
  41         randseed = seed;
  42 }
  43
  44 /*
  45  * Pseudo-random number generator for randomizing the profiling clock,
  46  * and whatever else we might use it for.  The result is uniform on
  47  * [0, 2^31 - 1].
  48  */
  49 u_long
  50 krandom(void)
  51 {
  52         long x, hi, lo, t;
  53
  54         /*
  55          * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
  56          * From "Random number generators: good ones are hard to find",
  57          * Park and Miller, Communications of the ACM, vol. 31, no. 10,
  58          * October 1988, p. 1195.
  59          */
  60         x = randseed;
  61         hi = x / 127773;
  62         lo = x % 127773;
  63         t = 16807 * lo - 2836 * hi;
  64         if (t <= 0)
  65                 t += 0x7fffffff;
  66         randseed = t;
  67         return (t);
  68 }