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Annotation of kernel/bsd/libkern/random.c, revision 1.1.1.1

1.1       root        1: /*
                      2:  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
                      3:  *
                      4:  * @APPLE_LICENSE_HEADER_START@
                      5:  * 
                      6:  * Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
                      7:  * Reserved.  This file contains Original Code and/or Modifications of
                      8:  * Original Code as defined in and that are subject to the Apple Public
                      9:  * Source License Version 1.1 (the "License").  You may not use this file
                     10:  * except in compliance with the License.  Please obtain a copy of the
                     11:  * License at http://www.apple.com/publicsource and read it before using
                     12:  * this file.
                     13:  * 
                     14:  * The Original Code and all software distributed under the License are
                     15:  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
                     16:  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
                     17:  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
                     18:  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
                     19:  * License for the specific language governing rights and limitations
                     20:  * under the License.
                     21:  * 
                     22:  * @APPLE_LICENSE_HEADER_END@
                     23:  */
                     24: 
                     25: /*-
                     26:  * Copyright (c) 1992, 1993
                     27:  *     The Regents of the University of California.  All rights reserved.
                     28:  *
                     29:  * Redistribution and use in source and binary forms, with or without
                     30:  * modification, are permitted provided that the following conditions
                     31:  * are met:
                     32:  * 1. Redistributions of source code must retain the above copyright
                     33:  *    notice, this list of conditions and the following disclaimer.
                     34:  * 2. Redistributions in binary form must reproduce the above copyright
                     35:  *    notice, this list of conditions and the following disclaimer in the
                     36:  *    documentation and/or other materials provided with the distribution.
                     37:  * 3. All advertising materials mentioning features or use of this software
                     38:  *    must display the following acknowledgement:
                     39:  *     This product includes software developed by the University of
                     40:  *     California, Berkeley and its contributors.
                     41:  * 4. Neither the name of the University nor the names of its contributors
                     42:  *    may be used to endorse or promote products derived from this software
                     43:  *    without specific prior written permission.
                     44:  *
                     45:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
                     46:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
                     47:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
                     48:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
                     49:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
                     50:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
                     51:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
                     52:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
                     53:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
                     54:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
                     55:  * SUCH DAMAGE.
                     56:  *
                     57:  *     @(#)random.c    8.1 (Berkeley) 6/10/93
                     58:  */
                     59: 
                     60: #include <libkern/libkern.h>
                     61: 
                     62: /*
                     63:  * Pseudo-random number generator for randomizing the profiling clock,
                     64:  * and whatever else we might use it for.  The result is uniform on
                     65:  * [0, 2^31 - 1].
                     66:  */
                     67: u_long
                     68: random()
                     69: {
                     70:        static u_long randseed = 1;
                     71:        register long x, hi, lo, t;
                     72: 
                     73:        /*
                     74:         * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
                     75:         * From "Random number generators: good ones are hard to find",
                     76:         * Park and Miller, Communications of the ACM, vol. 31, no. 10,
                     77:         * October 1988, p. 1195.
                     78:         */
                     79:        x = randseed;
                     80:        hi = x / 127773;
                     81:        lo = x % 127773;
                     82:        t = 16807 * lo - 2836 * hi;
                     83:        if (t <= 0)
                     84:                t += 0x7fffffff;
                     85:        randseed = t;
                     86:        return (t);
                     87: }

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