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 <sys/types.h> 42 #include <stdlib.h> 43 #include "un-namespace.h" 44 45 #ifdef TEST 46 #include <stdio.h> 47 #endif /* TEST */ 48 49 static int 50 do_rand(unsigned long *ctx) 51 { 52 #ifdef USE_WEAK_SEEDING 53 /* 54 * Historic implementation compatibility. 55 * The random sequences do not vary much with the seed, 56 * even with overflowing. 57 */ 58 return ((*ctx = *ctx * 1103515245 + 12345) % ((u_long)RAND_MAX + 1)); 59 #else /* !USE_WEAK_SEEDING */ 60 /* 61 * Compute x = (7^5 * x) mod (2^31 - 1) 62 * without overflowing 31 bits: 63 * (2^31 - 1) = 127773 * (7^5) + 2836 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 long hi, lo, x; 69 70 /* Must be in [1, 0x7ffffffe] range at this point. */ 71 hi = *ctx / 127773; 72 lo = *ctx % 127773; 73 x = 16807 * lo - 2836 * hi; 74 if (x < 0) 75 x += 0x7fffffff; 76 *ctx = x; 77 /* Transform to [0, 0x7ffffffd] range. */ 78 return (x - 1); 79 #endif /* !USE_WEAK_SEEDING */ 80 } 81 82 83 int 84 rand_r(unsigned int *ctx) 85 { 86 u_long val; 87 int r; 88 89 #ifdef USE_WEAK_SEEDING 90 val = *ctx; 91 #else 92 /* Transform to [1, 0x7ffffffe] range. */ 93 val = (*ctx % 0x7ffffffe) + 1; 94 #endif 95 r = do_rand(&val); 96 97 #ifdef USE_WEAK_SEEDING 98 *ctx = (unsigned int)val; 99 #else 100 *ctx = (unsigned int)(val - 1); 101 #endif 102 return (r); 103 } 104 105 106 static u_long next = 107 #ifdef USE_WEAK_SEEDING 108 1; 109 #else 110 2; 111 #endif 112 113 int 114 rand() 115 { 116 return (do_rand(&next)); 117 } 118 119 void 120 srand(seed) 121 u_int seed; 122 { 123 next = seed; 124 #ifndef USE_WEAK_SEEDING 125 /* Transform to [1, 0x7ffffffe] range. */ 126 next = (next % 0x7ffffffe) + 1; 127 #endif 128 } 129 130 131 /* 132 * sranddev: 133 * 134 * Many programs choose the seed value in a totally predictable manner. 135 * This often causes problems. We seed the generator using pseudo-random 136 * data from the kernel. 137 */ 138 void 139 sranddev() 140 { 141 int mib[2]; 142 size_t len; 143 144 len = sizeof(next); 145 146 mib[0] = CTL_KERN; 147 mib[1] = KERN_ARND; 148 sysctl(mib, 2, (void *)&next, &len, NULL, 0); 149 #ifndef USE_WEAK_SEEDING 150 /* Transform to [1, 0x7ffffffe] range. */ 151 next = (next % 0x7ffffffe) + 1; 152 #endif 153 } 154 155 156 #ifdef TEST 157 158 main() 159 { 160 int i; 161 unsigned myseed; 162 163 printf("seeding rand with 0x19610910: \n"); 164 srand(0x19610910); 165 166 printf("generating three pseudo-random numbers:\n"); 167 for (i = 0; i < 3; i++) 168 { 169 printf("next random number = %d\n", rand()); 170 } 171 172 printf("generating the same sequence with rand_r:\n"); 173 myseed = 0x19610910; 174 for (i = 0; i < 3; i++) 175 { 176 printf("next random number = %d\n", rand_r(&myseed)); 177 } 178 179 return 0; 180 } 181 182 #endif /* TEST */ 183 184