rand.c revision 92986
1258299Sjmmv/*- 2258299Sjmmv * Copyright (c) 1990, 1993 3258299Sjmmv * The Regents of the University of California. All rights reserved. 4258299Sjmmv * 5258299Sjmmv * Redistribution and use in source and binary forms, with or without 6258299Sjmmv * modification, are permitted provided that the following conditions 7258299Sjmmv * are met: 8258299Sjmmv * 1. Redistributions of source code must retain the above copyright 9258299Sjmmv * notice, this list of conditions and the following disclaimer. 10258299Sjmmv * 2. Redistributions in binary form must reproduce the above copyright 11258299Sjmmv * notice, this list of conditions and the following disclaimer in the 12258299Sjmmv * documentation and/or other materials provided with the distribution. 13258299Sjmmv * 3. All advertising materials mentioning features or use of this software 14258299Sjmmv * must display the following acknowledgement: 15258299Sjmmv * This product includes software developed by the University of 16258299Sjmmv * California, Berkeley and its contributors. 17258299Sjmmv * 4. Neither the name of the University nor the names of its contributors 18258299Sjmmv * may be used to endorse or promote products derived from this software 19258299Sjmmv * without specific prior written permission. 20258299Sjmmv * 21258299Sjmmv * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22258299Sjmmv * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23258299Sjmmv * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24258299Sjmmv * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25258299Sjmmv * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26258299Sjmmv * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27258299Sjmmv * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28258299Sjmmv * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29258299Sjmmv * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30258299Sjmmv * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31258299Sjmmv * SUCH DAMAGE. 32258299Sjmmv * 33258299Sjmmv * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>. 34258299Sjmmv */ 35258299Sjmmv 36258299Sjmmv#if defined(LIBC_SCCS) && !defined(lint) 37258299Sjmmvstatic char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93"; 38258299Sjmmv#endif /* LIBC_SCCS and not lint */ 39258299Sjmmv#include <sys/cdefs.h> 40258299Sjmmv__FBSDID("$FreeBSD: head/lib/libc/stdlib/rand.c 92986 2002-03-22 21:53:29Z obrien $"); 41258299Sjmmv 42258299Sjmmv#include <sys/time.h> /* for sranddev() */ 43258299Sjmmv#include <sys/types.h> 44258299Sjmmv#include <fcntl.h> /* for sranddev() */ 45258299Sjmmv#include <stdlib.h> 46258299Sjmmv#include <unistd.h> /* for sranddev() */ 47258299Sjmmv#include "un-namespace.h" 48258299Sjmmv 49258299Sjmmv#ifdef TEST 50258299Sjmmv#include <stdio.h> 51258299Sjmmv#endif /* TEST */ 52258299Sjmmv 53258299Sjmmvstatic int 54258299Sjmmvdo_rand(unsigned long *ctx) 55258299Sjmmv{ 56258299Sjmmv#ifdef USE_WEAK_SEEDING 57258299Sjmmv/* 58258299Sjmmv * Historic implementation compatibility. 59258299Sjmmv * The random sequences do not vary much with the seed, 60258299Sjmmv * even with overflowing. 61258299Sjmmv */ 62258299Sjmmv return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1)); 63258299Sjmmv#else /* !USE_WEAK_SEEDING */ 64258299Sjmmv/* 65258299Sjmmv * Compute x = (7^5 * x) mod (2^31 - 1) 66258299Sjmmv * wihout overflowing 31 bits: 67258299Sjmmv * (2^31 - 1) = 127773 * (7^5) + 2836 68258299Sjmmv * From "Random number generators: good ones are hard to find", 69258299Sjmmv * Park and Miller, Communications of the ACM, vol. 31, no. 10, 70258299Sjmmv * October 1988, p. 1195. 71258299Sjmmv */ 72258299Sjmmv long hi, lo, x; 73258299Sjmmv 74258299Sjmmv hi = *ctx / 127773; 75258299Sjmmv lo = *ctx % 127773; 76258299Sjmmv x = 16807 * lo - 2836 * hi; 77258299Sjmmv if (x <= 0) 78258299Sjmmv x += 0x7fffffff; 79258299Sjmmv return ((*ctx = x) % ((u_long)RAND_MAX + 1)); 80258299Sjmmv#endif /* !USE_WEAK_SEEDING */ 81258299Sjmmv} 82258299Sjmmv 83258299Sjmmv 84258299Sjmmvint 85258299Sjmmvrand_r(unsigned int *ctx) 86258299Sjmmv{ 87258299Sjmmv u_long val = (u_long) *ctx; 88258299Sjmmv *ctx = do_rand(&val); 89258299Sjmmv return (int) *ctx; 90258299Sjmmv} 91258299Sjmmv 92258299Sjmmv 93258299Sjmmvstatic u_long next = 1; 94258299Sjmmv 95258299Sjmmvint 96258299Sjmmvrand() 97258299Sjmmv{ 98258299Sjmmv return do_rand(&next); 99258299Sjmmv} 100258299Sjmmv 101258299Sjmmvvoid 102258299Sjmmvsrand(seed) 103258299Sjmmvu_int seed; 104258299Sjmmv{ 105258299Sjmmv next = seed; 106258299Sjmmv} 107258299Sjmmv 108258299Sjmmv 109258299Sjmmv/* 110258299Sjmmv * sranddev: 111258299Sjmmv * 112258299Sjmmv * Many programs choose the seed value in a totally predictable manner. 113258299Sjmmv * This often causes problems. We seed the generator using the much more 114258299Sjmmv * secure random(4) interface. 115258299Sjmmv */ 116258299Sjmmvvoid 117258299Sjmmvsranddev() 118258299Sjmmv{ 119258299Sjmmv int fd, done; 120 121 done = 0; 122 fd = _open("/dev/random", O_RDONLY, 0); 123 if (fd >= 0) { 124 if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next)) 125 done = 1; 126 _close(fd); 127 } 128 129 if (!done) { 130 struct timeval tv; 131 unsigned long junk; 132 133 gettimeofday(&tv, NULL); 134 next = (getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk; 135 } 136} 137 138 139#ifdef TEST 140 141main() 142{ 143 int i; 144 unsigned myseed; 145 146 printf("seeding rand with 0x19610910: \n"); 147 srand(0x19610910); 148 149 printf("generating three pseudo-random numbers:\n"); 150 for (i = 0; i < 3; i++) 151 { 152 printf("next random number = %d\n", rand()); 153 } 154 155 printf("generating the same sequence with rand_r:\n"); 156 myseed = 0x19610910; 157 for (i = 0; i < 3; i++) 158 { 159 printf("next random number = %d\n", rand_r(&myseed)); 160 } 161 162 return 0; 163} 164 165#endif /* TEST */ 166 167