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root/usr/lib/libc/stdlib/random.c

DEFINITIONS

1. srandom
2. random

   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  * 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  *      @(#)random.c    8.1 (Berkeley) 6/10/93
  30  */
  32 #include <sys/cdefs.h>
  33 #include <sys/types.h>
  34 #include <stdlib.h>
  36 #define NSHUFF 50       /* to drop some "seed -> 1st value" linearity */
  38 static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
  40 void
srandom(seed)
u_long seed;
  43 {
  44         int i;
randseed = seed;
  47         for (i = 0; i < NSHUFF; i++)
  48                 (void)random();
  49 }
  51 /*
  52  * Pseudo-random number generator for randomizing the profiling clock,
  53  * and whatever else we might use it for.  The result is uniform on
  54  * [0, 2^31 - 1].
  55  */
  56 long
random()
  58 {
  59         long x, hi, lo, t;
  61         /*
  62          * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
  63          * From "Random number generators: good ones are hard to find",
  64          * Park and Miller, Communications of the ACM, vol. 31, no. 10,
  65          * October 1988, p. 1195.
  66          */
  67         /* Can't be initialized with 0, so use another value. */
  68         if ((x = randseed) == 0)
x = 123459876;
hi = x / 127773;
lo = x % 127773;
t = 16807 * lo - 2836 * hi;
  73         if (t < 0)
t += 0x7fffffff;
randseed = t;
  76         return (t);
  77 }