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Annotation of sys/lib/libkern/random.c, Revision 1.1

1.1     ! nbrk        1: /*     $OpenBSD: random.c,v 1.7 2004/08/07 00:38:33 deraadt Exp $      */
        !             2: /*     $NetBSD: random.c,v 1.2 1994/10/26 06:42:42 cgd Exp $   */
        !             3:
        !             4: /*-
        !             5:  * Copyright (c) 1992, 1993
        !             6:  *     The Regents of the University of California.  All rights reserved.
        !             7:  *
        !             8:  * Redistribution and use in source and binary forms, with or without
        !             9:  * modification, are permitted provided that the following conditions
        !            10:  * are met:
        !            11:  * 1. Redistributions of source code must retain the above copyright
        !            12:  *    notice, this list of conditions and the following disclaimer.
        !            13:  * 2. Redistributions in binary form must reproduce the above copyright
        !            14:  *    notice, this list of conditions and the following disclaimer in the
        !            15:  *    documentation and/or other materials provided with the distribution.
        !            16:  * 3. Neither the name of the University nor the names of its contributors
        !            17:  *    may be used to endorse or promote products derived from this software
        !            18:  *    without specific prior written permission.
        !            19:  *
        !            20:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            21:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            22:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            23:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            24:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            25:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            26:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            27:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            28:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            29:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            30:  * SUCH DAMAGE.
        !            31:  *
        !            32:  *     @(#)random.c    8.1 (Berkeley) 6/10/93
        !            33:  */
        !            34:
        !            35: #include <sys/types.h>
        !            36:
        !            37: #include <lib/libkern/libkern.h>
        !            38:
        !            39: /*
        !            40:  * Pseudo-random number generator for randomizing the profiling clock,
        !            41:  * and whatever else we might use it for.  The result is uniform on
        !            42:  * [0, 2^31 - 1].
        !            43:  */
        !            44: u_long _randseed = 1;
        !            45:
        !            46: u_long
        !            47: random(void)
        !            48: {
        !            49:        long x, hi, lo, t;
        !            50:
        !            51:        /*
        !            52:         * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
        !            53:         * From "Random number generators: good ones are hard to find",
        !            54:         * Park and Miller, Communications of the ACM, vol. 31, no. 10,
        !            55:         * October 1988, p. 1195.
        !            56:         */
        !            57:        x = _randseed;
        !            58:        hi = x / 127773;
        !            59:        lo = x % 127773;
        !            60:        t = 16807 * lo - 2836 * hi;
        !            61:        if (t <= 0)
        !            62:                t += 0x7fffffff;
        !            63:        _randseed = t;
        !            64:        return (t);
        !            65: }