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 * @(#)rand.c 8.1 (Berkeley) 6/14/93 32 * $FreeBSD: src/lib/libc/stdlib/rand.c,v 1.17 2007/12/11 20:39:32 ache Exp $ 33 */ 34 35 #include "namespace.h" 36 #include <sys/time.h> /* for sranddev() */ 37 #include <sys/types.h> 38 #include <fcntl.h> /* for sranddev() */ 39 #include <stdlib.h> 40 #include <unistd.h> /* for sranddev() */ 41 #include "un-namespace.h" 42 43 #ifdef TEST 44 #include <stdio.h> 45 #endif /* TEST */ 46 47 /* 48 * Compute x = (7^5 * x) mod (2^31 - 1) 49 * without overflowing 31 bits: 50 * (2^31 - 1) = 127773 * (7^5) + 2836 51 * From "Random number generators: good ones are hard to find", 52 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 53 * October 1988, p. 1195. 54 */ 55 static int 56 do_rand(unsigned long *ctx) 57 { 58 long hi, lo, x; 59 60 /* Can't be initialized with 0, so use another value. */ 61 if (*ctx == 0) 62 *ctx = 123459876; 63 hi = *ctx / 127773; 64 lo = *ctx % 127773; 65 x = 16807 * lo - 2836 * hi; 66 if (x < 0) 67 x += 0x7fffffff; 68 return ((*ctx = x) % ((u_long)RAND_MAX + 1)); 69 } 70 71 72 int 73 rand_r(unsigned int *ctx) 74 { 75 u_long val = (u_long) *ctx; 76 int r = do_rand(&val); 77 78 *ctx = (unsigned int) val; 79 return (r); 80 } 81 82 83 static u_long next = 1; 84 85 int 86 rand(void) 87 { 88 return (do_rand(&next)); 89 } 90 91 void 92 srand(u_int seed) 93 { 94 next = seed; 95 } 96 97 98 /* 99 * sranddev: 100 * 101 * Many programs choose the seed value in a totally predictable manner. 102 * This often causes problems. We seed the generator using the much more 103 * secure random(4) interface. 104 */ 105 void 106 sranddev(void) 107 { 108 int fd, done; 109 110 done = 0; 111 fd = _open("/dev/random", O_RDONLY, 0); 112 if (fd >= 0) { 113 if (_read(fd, (void *) &next, sizeof(next)) == sizeof(next)) 114 done = 1; 115 _close(fd); 116 } 117 118 if (!done) { 119 struct timeval tv; 120 unsigned long junk; /* XXX left uninitialized on purpose */ 121 122 gettimeofday(&tv, NULL); 123 srand((getpid() << 16) ^ tv.tv_sec ^ tv.tv_usec ^ junk); 124 } 125 } 126 127 128 #ifdef TEST 129 130 int 131 main(int argc __unused, char *argv[] __unused) 132 { 133 int i; 134 unsigned myseed; 135 136 printf("seeding rand with 0x19610910: \n"); 137 srand(0x19610910); 138 139 printf("generating three pseudo-random numbers:\n"); 140 for (i = 0; i < 3; i++) 141 { 142 printf("next random number = %d\n", rand()); 143 } 144 145 printf("generating the same sequence with rand_r:\n"); 146 myseed = 0x19610910; 147 for (i = 0; i < 3; i++) 148 { 149 printf("next random number = %d\n", rand_r(&myseed)); 150 } 151 152 return 0; 153 } 154 155 #endif /* TEST */ 156 157