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Annotation of sys/lib/libkern/random.c, Revision 1.1.1.1

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: }