The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/libkern/random.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1992, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  * 3. Neither the name of the University nor the names of its contributors
   16  *    may be used to endorse or promote products derived from this software
   17  *    without specific prior written permission.
   18  *
   19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   29  * SUCH DAMAGE.
   30  *
   31  *      @(#)random.c    8.1 (Berkeley) 6/10/93
   32  */
   33 
   34 #include <sys/cdefs.h>
   35 __FBSDID("$FreeBSD: releng/12.0/sys/libkern/random.c 326023 2017-11-20 19:43:44Z pfg $");
   36 
   37 #include <sys/libkern.h>
   38 
   39 #define NSHUFF 50       /* to drop some "seed -> 1st value" linearity */
   40 
   41 static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
   42 
   43 void
   44 srandom(u_long seed)
   45 {
   46         int i;
   47 
   48         randseed = seed;
   49         for (i = 0; i < NSHUFF; i++)
   50                 (void)random();
   51 }
   52 
   53 /*
   54  * Pseudo-random number generator for perturbing the profiling clock,
   55  * and whatever else we might use it for.  The result is uniform on
   56  * [0, 2^31 - 1].
   57  */
   58 u_long
   59 random()
   60 {
   61         long x, hi, lo, t;
   62 
   63         /*
   64          * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
   65          * From "Random number generators: good ones are hard to find",
   66          * Park and Miller, Communications of the ACM, vol. 31, no. 10,
   67          * October 1988, p. 1195.
   68          */
   69         /* Can't be initialized with 0, so use another value. */
   70         if ((x = randseed) == 0)
   71                 x = 123459876;
   72         hi = x / 127773;
   73         lo = x % 127773;
   74         t = 16807 * lo - 2836 * hi;
   75         if (t < 0)
   76                 t += 0x7fffffff;
   77         randseed = t;
   78         return (t);
   79 }

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