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 * 4. 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 /* Can't be initialized with 0, so use another value. */ 71 if (*ctx == 0) 72 *ctx = 123459876; 73 hi = *ctx / 127773; 74 lo = *ctx % 127773; 75 x = 16807 * lo - 2836 * hi; 76 if (x < 0) 77 x += 0x7fffffff; 78 return ((*ctx = x) % ((u_long)RAND_MAX + 1)); 79 #endif /* !USE_WEAK_SEEDING */ 80 } 81 82 83 int 84 rand_r(unsigned int *ctx) 85 { 86 u_long val = (u_long) *ctx; 87 int r = do_rand(&val); 88 89 *ctx = (unsigned int) val; 90 return (r); 91 } 92 93 94 static u_long next = 1; 95 96 int 97 rand() 98 { 99 return (do_rand(&next)); 100 } 101 102 void 103 srand(seed) 104 u_int seed; 105 { 106 next = seed; 107 } 108 109 110 /* 111 * sranddev: 112 * 113 * Many programs choose the seed value in a totally predictable manner. 114 * This often causes problems. We seed the generator using pseudo-random 115 * data from the kernel. 116 */ 117 void 118 sranddev() 119 { 120 int mib[2]; 121 size_t len; 122 123 len = sizeof(next); 124 125 mib[0] = CTL_KERN; 126 mib[1] = KERN_ARND; 127 sysctl(mib, 2, (void *)&next, &len, NULL, 0); 128 } 129 130 131 #ifdef TEST 132 133 main() 134 { 135 int i; 136 unsigned myseed; 137 138 printf("seeding rand with 0x19610910: \n"); 139 srand(0x19610910); 140 141 printf("generating three pseudo-random numbers:\n"); 142 for (i = 0; i < 3; i++) 143 { 144 printf("next random number = %d\n", rand()); 145 } 146 147 printf("generating the same sequence with rand_r:\n"); 148 myseed = 0x19610910; 149 for (i = 0; i < 3; i++) 150 { 151 printf("next random number = %d\n", rand_r(&myseed)); 152 } 153 154 return 0; 155 } 156 157 #endif /* TEST */ 158 159