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Annotation of prex-old/usr/lib/libc/stdlib/random.c, Revision 1.1.1.1

1.1       nbrk        1: /*-
                      2:  * Copyright (c) 1992, 1993
                      3:  *     The Regents of the University of California.  All rights reserved.
                      4:  *
                      5:  * Redistribution and use in source and binary forms, with or without
                      6:  * modification, are permitted provided that the following conditions
                      7:  * are met:
                      8:  * 1. Redistributions of source code must retain the above copyright
                      9:  *    notice, this list of conditions and the following disclaimer.
                     10:  * 2. Redistributions in binary form must reproduce the above copyright
                     11:  *    notice, this list of conditions and the following disclaimer in the
                     12:  *    documentation and/or other materials provided with the distribution.
                     13:  * 4. Neither the name of the University nor the names of its contributors
                     14:  *    may be used to endorse or promote products derived from this software
                     15:  *    without specific prior written permission.
                     16:  *
                     17:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
                     18:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
                     19:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
                     20:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
                     21:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
                     22:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
                     23:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
                     24:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
                     25:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
                     26:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
                     27:  * SUCH DAMAGE.
                     28:  *
                     29:  *     @(#)random.c    8.1 (Berkeley) 6/10/93
                     30:  */
                     31:
                     32: #include <sys/cdefs.h>
                     33: #include <sys/types.h>
                     34: #include <stdlib.h>
                     35:
                     36: #define NSHUFF 50       /* to drop some "seed -> 1st value" linearity */
                     37:
                     38: static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
                     39:
                     40: void
                     41: srandom(seed)
                     42:        u_long seed;
                     43: {
                     44:        int i;
                     45:
                     46:        randseed = seed;
                     47:        for (i = 0; i < NSHUFF; i++)
                     48:                (void)random();
                     49: }
                     50:
                     51: /*
                     52:  * Pseudo-random number generator for randomizing the profiling clock,
                     53:  * and whatever else we might use it for.  The result is uniform on
                     54:  * [0, 2^31 - 1].
                     55:  */
                     56: long
                     57: random()
                     58: {
                     59:        long x, hi, lo, t;
                     60:
                     61:        /*
                     62:         * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
                     63:         * From "Random number generators: good ones are hard to find",
                     64:         * Park and Miller, Communications of the ACM, vol. 31, no. 10,
                     65:         * October 1988, p. 1195.
                     66:         */
                     67:        /* Can't be initialized with 0, so use another value. */
                     68:        if ((x = randseed) == 0)
                     69:                x = 123459876;
                     70:        hi = x / 127773;
                     71:        lo = x % 127773;
                     72:        t = 16807 * lo - 2836 * hi;
                     73:        if (t < 0)
                     74:                t += 0x7fffffff;
                     75:        randseed = t;
                     76:        return (t);
                     77: }