1 /*- 2 * Copyright (c) 1990, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>. 34 * 35 * $FreeBSD: src/lib/libc/stdlib/rand.c,v 1.15 2001/03/05 11:33:57 ache Exp $ 36 * $DragonFly: src/lib/libc/stdlib/rand.c,v 1.3 2004/05/17 07:35:55 dillon Exp $ 37 */ 38 39 #if defined(LIBC_SCCS) && !defined(lint) 40 static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93"; 41 #endif /* LIBC_SCCS and not lint */ 42 #include <sys/cdefs.h> 43 44 #include <sys/time.h> /* for sranddev() */ 45 #include <sys/types.h> 46 #include <fcntl.h> /* for sranddev() */ 47 #include <stdlib.h> 48 #include <unistd.h> /* for sranddev() */ 49 50 #ifdef TEST 51 #include <stdio.h> 52 #endif /* TEST */ 53 54 static int 55 do_rand(unsigned long *ctx) 56 { 57 #ifdef USE_WEAK_SEEDING 58 /* 59 * Historic implementation compatibility. 60 * The random sequences do not vary much with the seed, 61 * even with overflowing. 62 */ 63 return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1)); 64 #else /* !USE_WEAK_SEEDING */ 65 /* 66 * Compute x = (7^5 * x) mod (2^31 - 1) 67 * wihout overflowing 31 bits: 68 * (2^31 - 1) = 127773 * (7^5) + 2836 69 * From "Random number generators: good ones are hard to find", 70 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 71 * October 1988, p. 1195. 72 */ 73 long hi, lo, x; 74 75 /* Can't be initialized with 0, so use another value. */ 76 if (*ctx == 0) 77 *ctx = 123459876; 78 hi = *ctx / 127773; 79 lo = *ctx % 127773; 80 x = 16807 * lo - 2836 * hi; 81 if (x < 0) 82 x += 0x7fffffff; 83 return ((*ctx = x) % ((u_long)RAND_MAX + 1)); 84 #endif /* !USE_WEAK_SEEDING */ 85 } 86 87 88 int 89 rand_r(unsigned int *ctx) 90 { 91 u_long val = (u_long) *ctx; 92 int r = do_rand(&val); 93 94 *ctx = (unsigned int) val; 95 return (r); 96 } 97 98 99 static u_long next = 1; 100 101 int 102 rand() 103 { 104 return (do_rand(&next)); 105 } 106 107 void 108 srand(seed) 109 u_int seed; 110 { 111 next = seed; 112 } 113 114 115 /* 116 * sranddev: 117 * 118 * Many programs choose the seed value in a totally predictable manner. 119 * This often causes problems. We seed the generator using the much more 120 * secure random(4) interface. 121 * 122 * FreeBSD chooses to use /dev/random for their seed. However, because 123 * of possible problems surrounding /dev/random, we use /dev/urandom for now, 124 * which is guaranteed not to block and will produce a "good enough" seed 125 * for us for the time being. 126 */ 127 void 128 sranddev() 129 { 130 int fd, done; 131 132 done = 0; 133 fd = _open("/dev/urandom", O_RDONLY, 0); 134 if (fd >= 0) { 135 if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next)) 136 done = 1; 137 _close(fd); 138 } 139 140 if (!done) { 141 struct timeval tv; 142 unsigned long junk; 143 144 gettimeofday(&tv, NULL); 145 srand((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk); 146 } 147 } 148 149 150 #ifdef TEST 151 152 main() 153 { 154 int i; 155 unsigned myseed; 156 157 printf("seeding rand with 0x19610910: \n"); 158 srand(0x19610910); 159 160 printf("generating three pseudo-random numbers:\n"); 161 for (i = 0; i < 3; i++) 162 { 163 printf("next random number = %d\n", rand()); 164 } 165 166 printf("generating the same sequence with rand_r:\n"); 167 myseed = 0x19610910; 168 for (i = 0; i < 3; i++) 169 { 170 printf("next random number = %d\n", rand_r(&myseed)); 171 } 172 173 return 0; 174 } 175 176 #endif /* TEST */ 177 178