random.c

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/*-
 * Copyright (c) 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)random.c    8.1 (Berkeley) 6/10/93
 */

#include <sys/cdefs.h>
__FBSDID("$BSDSUniX$");

#include <sys/libkern.h>

#define NSHUFF 50       /* to drop some "seed -> 1st value" linearity */

static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */

void
srandom(seed)
        u_long seed;
{
        int i;

        randseed = seed;
        for (i = 0; i < NSHUFF; i++)
                (void)random();
}

/*
 * Pseudo-random number generator for randomizing the profiling clock,
 * and whatever else we might use it for.  The result is uniform on
 * [0, 2^31 - 1].
 */
u_long
random()
{
        register long x, hi, lo, t;

        /*
         * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
         * From "Random number generators: good ones are hard to find",
         * Park and Miller, Communications of the ACM, vol. 31, no. 10,
         * October 1988, p. 1195.
         */
        /* Can't be initialized with 0, so use another value. */
        if ((x = randseed) == 0)
                x = 123459876;
        hi = x / 127773;
        lo = x % 127773;
        t = 16807 * lo - 2836 * hi;
        if (t < 0)
                t += 0x7fffffff;
        randseed = t;
        return (t);
}