1 /* $OpenBSD: random.c,v 1.5 1997/11/07 15:56:49 niklas 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. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)random.c 8.1 (Berkeley) 6/10/93 37 */ 38 39 #include <sys/types.h> 40 41 #include <lib/libkern/libkern.h> 42 43 /* 44 * Pseudo-random number generator for randomizing the profiling clock, 45 * and whatever else we might use it for. The result is uniform on 46 * [0, 2^31 - 1]. 47 */ 48 u_long _randseed = 1; 49 50 u_long 51 random() 52 { 53 register long x, hi, lo, t; 54 55 /* 56 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1). 57 * From "Random number generators: good ones are hard to find", 58 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 59 * October 1988, p. 1195. 60 */ 61 x = _randseed; 62 hi = x / 127773; 63 lo = x % 127773; 64 t = 16807 * lo - 2836 * hi; 65 if (t <= 0) 66 t += 0x7fffffff; 67 _randseed = t; 68 return (t); 69 } 70