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. Neither the name of the University nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>. 30 */ 31 32 #if defined(LIBC_SCCS) && !defined(lint) 33 static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93"; 34 #endif /* LIBC_SCCS and not lint */ 35 #include <sys/cdefs.h> 36 __FBSDID("$FreeBSD$"); 37 38 #include "namespace.h" 39 #include <sys/param.h> 40 #include <sys/sysctl.h> 41 #include <stdlib.h> 42 #include "un-namespace.h" 43 44 #ifdef TEST 45 #include <stdio.h> 46 #endif /* TEST */ 47 48 static int 49 do_rand(unsigned long *ctx) 50 { 51 #ifdef USE_WEAK_SEEDING 52 /* 53 * Historic implementation compatibility. 54 * The random sequences do not vary much with the seed, 55 * even with overflowing. 56 */ 57 return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1)); 58 #else /* !USE_WEAK_SEEDING */ 59 /* 60 * Compute x = (7^5 * x) mod (2^31 - 1) 61 * without overflowing 31 bits: 62 * (2^31 - 1) = 127773 * (7^5) + 2836 63 * From "Random number generators: good ones are hard to find", 64 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 65 * October 1988, p. 1195. 66 */ 67 long hi, lo, x; 68 69 /* Must be in [1, 0x7ffffffe] range at this point. */ 70 hi = *ctx / 127773; 71 lo = *ctx % 127773; 72 x = 16807 * lo - 2836 * hi; 73 if (x < 0) 74 x += 0x7fffffff; 75 *ctx = x; 76 /* Transform to [0, 0x7ffffffd] range. */ 77 return (x - 1); 78 #endif /* !USE_WEAK_SEEDING */ 79 } 80 81 82 int 83 rand_r(unsigned int *ctx) 84 { 85 u_long val; 86 int r; 87 88 #ifdef USE_WEAK_SEEDING 89 val = *ctx; 90 #else 91 /* Transform to [1, 0x7ffffffe] range. */ 92 val = (*ctx % 0x7ffffffe) + 1; 93 #endif 94 r = do_rand(&val); 95 96 #ifdef USE_WEAK_SEEDING 97 *ctx = (unsigned int)val; 98 #else 99 *ctx = (unsigned int)(val - 1); 100 #endif 101 return (r); 102 } 103 104 105 static u_long next = 106 #ifdef USE_WEAK_SEEDING 107 1; 108 #else 109 2; 110 #endif 111 112 int 113 rand(void) 114 { 115 return (do_rand(&next)); 116 } 117 118 void 119 srand(u_int seed) 120 { 121 next = seed; 122 #ifndef USE_WEAK_SEEDING 123 /* Transform to [1, 0x7ffffffe] range. */ 124 next = (next % 0x7ffffffe) + 1; 125 #endif 126 } 127 128 129 /* 130 * sranddev: 131 * 132 * Many programs choose the seed value in a totally predictable manner. 133 * This often causes problems. We seed the generator using pseudo-random 134 * data from the kernel. 135 */ 136 void 137 sranddev(void) 138 { 139 int mib[2]; 140 size_t len; 141 142 len = sizeof(next); 143 144 mib[0] = CTL_KERN; 145 mib[1] = KERN_ARND; 146 sysctl(mib, 2, (void *)&next, &len, NULL, 0); 147 #ifndef USE_WEAK_SEEDING 148 /* Transform to [1, 0x7ffffffe] range. */ 149 next = (next % 0x7ffffffe) + 1; 150 #endif 151 } 152 153 154 #ifdef TEST 155 156 main() 157 { 158 int i; 159 unsigned myseed; 160 161 printf("seeding rand with 0x19610910: \n"); 162 srand(0x19610910); 163 164 printf("generating three pseudo-random numbers:\n"); 165 for (i = 0; i < 3; i++) 166 { 167 printf("next random number = %d\n", rand()); 168 } 169 170 printf("generating the same sequence with rand_r:\n"); 171 myseed = 0x19610910; 172 for (i = 0; i < 3; i++) 173 { 174 printf("next random number = %d\n", rand_r(&myseed)); 175 } 176 177 return 0; 178 } 179 180 #endif /* TEST */ 181 182