1 /* $OpenBSD: random.c,v 1.10 2017/09/08 05:36:53 deraadt 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. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 * 32 * @(#)random.c 8.1 (Berkeley) 6/10/93 33 */ 34 35 #include <sys/param.h> 36 37 #include <lib/libkern/libkern.h> 38 39 /* 40 * Pseudo-random number generator for randomizing the profiling clock. 41 * The result is uniform on [0, 2^31 - 1]. 42 */ 43 44 u_int32_t 45 random(void) 46 { 47 struct cpu_info *ci = curcpu(); 48 int32_t x, hi, lo, t; 49 50 /* 51 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1). 52 * From "Random number generators: good ones are hard to find", 53 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 54 * October 1988, p. 1195. 55 */ 56 x = ci->ci_randseed; 57 hi = x / 127773; 58 lo = x % 127773; 59 t = 16807 * lo - 2836 * hi; 60 if (t <= 0) 61 t += 0x7fffffff; 62 ci->ci_randseed = t; 63 return (t); 64 } 65