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scoutos / prex-0.9.0 / usr / lib / libc / stdlib / random.c @ 03e9c04a

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/*-
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 * Copyright (c) 1992, 1993
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 *        The Regents of the University of California.  All rights reserved.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer.
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 * 2. Redistributions in binary form must reproduce the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
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 *    documentation and/or other materials provided with the distribution.
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 * 4. Neither the name of the University nor the names of its contributors
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 *    may be used to endorse or promote products derived from this software
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 *    without specific prior written permission.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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 * SUCH DAMAGE.
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 *
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 *        @(#)random.c        8.1 (Berkeley) 6/10/93
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 */
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#include <sys/cdefs.h>
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#include <sys/types.h>
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#include <stdlib.h>
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#define NSHUFF 50       /* to drop some "seed -> 1st value" linearity */
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static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
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void
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srandom(seed)
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        u_long seed;
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{
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        int i;
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        randseed = seed;
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        for (i = 0; i < NSHUFF; i++)
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                (void)random();
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}
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/*
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 * Pseudo-random number generator for randomizing the profiling clock,
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 * and whatever else we might use it for.  The result is uniform on
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 * [0, 2^31 - 1].
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 */
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long
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random()
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{
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        long x, hi, lo, t;
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        /*
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         * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
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         * From "Random number generators: good ones are hard to find",
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         * Park and Miller, Communications of the ACM, vol. 31, no. 10,
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         * October 1988, p. 1195.
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         */
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        /* Can't be initialized with 0, so use another value. */
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        if ((x = randseed) == 0)
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                x = 123459876;
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        hi = x / 127773;
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        lo = x % 127773;
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        t = 16807 * lo - 2836 * hi;
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        if (t < 0)
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                t += 0x7fffffff;
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        randseed = t;
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        return (t);
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}