commands/swifi/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. 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  *      @(#)random.c    8.1 (Berkeley) 6/10/93
  34  */
  35
  36 #include "ddb.h"
  37
  38 static unsigned long randseed = 1;
  39
  40 void
  41 srandom(seed)
  42         unsigned long seed;
  43 {
  44         randseed = seed;
  45 }
  46
  47 /*
  48  * Pseudo-random number generator for randomizing the profiling clock,
  49  * and whatever else we might use it for.  The result is uniform on
  50  * [0, 2^31 - 1].
  51  */
  52 unsigned long
  53 random()
  54 {
  55         register long x, hi, lo, t;
  56
  57         /*
  58          * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
  59          * From "Random number generators: good ones are hard to find",
  60          * Park and Miller, Communications of the ACM, vol. 31, no. 10,
  61          * October 1988, p. 1195.
  62          */
  63         x = randseed;
  64         hi = x / 127773;
  65         lo = x % 127773;
  66         t = 16807 * lo - 2836 * hi;
  67         if (t <= 0)
  68                 t += 0x7fffffff;
  69         randseed = t;
  70         return (t);
  71 }