1 /* $NetBSD: random.c,v 1.2 1994/10/26 06:42:42 cgd Exp $ */ 2 3 /*- 4 * Copyright (c) 1992, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. All advertising materials mentioning features or use of this software 16 * must display the following acknowledgement: 17 * This product includes software developed by the University of 18 * California, Berkeley and its contributors. 19 * 4. Neither the name of the University nor the names of its contributors 20 * may be used to endorse or promote products derived from this software 21 * without specific prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33 * SUCH DAMAGE. 34 * 35 * @(#)random.c 8.1 (Berkeley) 6/10/93 36 */ 37 38 #include <sys/types.h> 39 40 #include <lib/libkern/libkern.h> 41 42 /* 43 * Pseudo-random number generator for randomizing the profiling clock, 44 * and whatever else we might use it for. The result is uniform on 45 * [0, 2^31 - 1]. 46 */ 47 u_long _randseed = 1; 48 49 u_long 50 random() 51 { 52 register long x, hi, lo, t; 53 54 /* 55 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1). 56 * From "Random number generators: good ones are hard to find", 57 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 58 * October 1988, p. 1195. 59 */ 60 x = _randseed; 61 hi = x / 127773; 62 lo = x % 127773; 63 t = 16807 * lo - 2836 * hi; 64 if (t <= 0) 65 t += 0x7fffffff; 66 _randseed = t; 67 return (t); 68 } 69