1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 1990, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of the University nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 * 31 * Posix rand_r function added May 1999 by Wes Peters <wes@softweyr.com>. 32 */ 33 34 #if defined(LIBC_SCCS) && !defined(lint) 35 static char sccsid[] = "@(#)rand.c 8.1 (Berkeley) 6/14/93"; 36 #endif /* LIBC_SCCS and not lint */ 37 #include <sys/cdefs.h> 38 __FBSDID("$FreeBSD$"); 39 40 #include "namespace.h" 41 #include <sys/param.h> 42 #include <sys/sysctl.h> 43 #include <stdlib.h> 44 #include "un-namespace.h" 45 46 #ifdef TEST 47 #include <stdio.h> 48 #endif /* TEST */ 49 50 static int 51 do_rand(unsigned long *ctx) 52 { 53 /* 54 * Compute x = (7^5 * x) mod (2^31 - 1) 55 * without overflowing 31 bits: 56 * (2^31 - 1) = 127773 * (7^5) + 2836 57 * From "Random number generators: good ones are hard to find", 58 * Park and Miller, Communications of the ACM, vol. 31, no. 10, 59 * October 1988, p. 1195. 60 */ 61 long hi, lo, x; 62 63 /* Transform to [1, 0x7ffffffe] range. */ 64 x = (*ctx % 0x7ffffffe) + 1; 65 hi = x / 127773; 66 lo = x % 127773; 67 x = 16807 * lo - 2836 * hi; 68 if (x < 0) 69 x += 0x7fffffff; 70 /* Transform to [0, 0x7ffffffd] range. */ 71 x--; 72 *ctx = x; 73 return (x); 74 } 75 76 77 int 78 rand_r(unsigned *ctx) 79 { 80 u_long val; 81 int r; 82 83 val = *ctx; 84 r = do_rand(&val); 85 *ctx = (unsigned)val; 86 return (r); 87 } 88 89 90 static u_long next = 1; 91 92 int 93 rand(void) 94 { 95 return (do_rand(&next)); 96 } 97 98 void 99 srand(unsigned seed) 100 { 101 next = seed; 102 } 103 104 105 /* 106 * sranddev: 107 * 108 * Many programs choose the seed value in a totally predictable manner. 109 * This often causes problems. We seed the generator using pseudo-random 110 * data from the kernel. 111 */ 112 void 113 sranddev(void) 114 { 115 int mib[2]; 116 size_t len; 117 118 len = sizeof(next); 119 120 mib[0] = CTL_KERN; 121 mib[1] = KERN_ARND; 122 sysctl(mib, 2, (void *)&next, &len, NULL, 0); 123 } 124 125 126 #ifdef TEST 127 128 main() 129 { 130 int i; 131 unsigned myseed; 132 133 printf("seeding rand with 0x19610910: \n"); 134 srand(0x19610910); 135 136 printf("generating three pseudo-random numbers:\n"); 137 for (i = 0; i < 3; i++) 138 { 139 printf("next random number = %d\n", rand()); 140 } 141 142 printf("generating the same sequence with rand_r:\n"); 143 myseed = 0x19610910; 144 for (i = 0; i < 3; i++) 145 { 146 printf("next random number = %d\n", rand_r(&myseed)); 147 } 148 149 return 0; 150 } 151 152 #endif /* TEST */ 153 154