1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 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. Neither the name of the University nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 * 31 * @(#)random.c 8.1 (Berkeley) 6/10/93 32 */ 33 34 #include <sys/cdefs.h> 35 __FBSDID("$FreeBSD$"); 36 37 #include <sys/types.h> 38 #include <sys/libkern.h> 39 #include <sys/systm.h> 40 41 static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */ 42 43 /* 44 * Pseudo-random number generator for perturbing 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 49 random(void) 50 { 51 static bool warned = false; 52 53 long x, hi, lo, t; 54 55 /* Warn only once, or it gets very spammy. */ 56 if (!warned) { 57 gone_in(13, 58 "random(9) is the obsolete Park-Miller LCG from 1988"); 59 warned = true; 60 } 61 62 /* 63 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1). 64 * From "Random number generators: good ones are hard to find", 65 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 66 * October 1988, p. 1195. 67 */ 68 /* Can't be initialized with 0, so use another value. */ 69 if ((x = randseed) == 0) 70 x = 123459876; 71 hi = x / 127773; 72 lo = x % 127773; 73 t = 16807 * lo - 2836 * hi; 74 if (t < 0) 75 t += 0x7fffffff; 76 randseed = t; 77 return (t); 78 } 79