1/* 2 * Copyright (C) 2004, 2005, 2007, 2009 Internet Systems Consortium, Inc. ("ISC") 3 * Copyright (C) 1999-2003 Internet Software Consortium. 4 * 5 * Permission to use, copy, modify, and/or distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH 10 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY 11 * AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, 12 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM 13 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE 14 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR 15 * PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18/* $Id: random.c,v 1.28 2009/07/16 05:52:46 marka Exp $ */ 19 20/*! \file */ 21 22#include <config.h> 23 24#include <stdlib.h> 25#include <time.h> /* Required for time(). */ 26#ifdef HAVE_SYS_TYPES_H 27#include <sys/types.h> 28#endif 29#ifdef HAVE_UNISTD_H 30#include <unistd.h> 31#endif 32 33#include <isc/mutex.h> 34#include <isc/once.h> 35#include <isc/random.h> 36#include <isc/string.h> 37#include <isc/util.h> 38 39static isc_once_t once = ISC_ONCE_INIT; 40 41static void 42initialize_rand(void) 43{ 44#ifndef HAVE_ARC4RANDOM 45 unsigned int pid = getpid(); 46 47 /* 48 * The low bits of pid generally change faster. 49 * Xor them with the high bits of time which change slowly. 50 */ 51 pid = ((pid << 16) & 0xffff0000) | ((pid >> 16) & 0xffff); 52 53 srand(time(NULL) ^ pid); 54#endif 55} 56 57static void 58initialize(void) 59{ 60 RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS); 61} 62 63void 64isc_random_seed(isc_uint32_t seed) 65{ 66 initialize(); 67 68#ifndef HAVE_ARC4RANDOM 69 srand(seed); 70#else 71 arc4random_addrandom((u_char *) &seed, sizeof(isc_uint32_t)); 72#endif 73} 74 75void 76isc_random_get(isc_uint32_t *val) 77{ 78 REQUIRE(val != NULL); 79 80 initialize(); 81 82#ifndef HAVE_ARC4RANDOM 83 /* 84 * rand()'s lower bits are not random. 85 * rand()'s upper bit is zero. 86 */ 87#if RAND_MAX >= 0xfffff 88 /* We have at least 20 bits. Use lower 16 excluding lower most 4 */ 89 *val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000); 90#elif RAND_MAX >= 0x7fff 91 /* We have at least 15 bits. Use lower 10/11 excluding lower most 4 */ 92 *val = ((rand() >> 4) & 0x000007ff) | ((rand() << 7) & 0x003ff800) | 93 ((rand() << 18) & 0xffc00000); 94#else 95#error RAND_MAX is too small 96#endif 97#else 98 *val = arc4random(); 99#endif 100} 101 102isc_uint32_t 103isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) { 104 isc_uint32_t rnd; 105 106 REQUIRE(jitter < max || (jitter == 0 && max == 0)); 107 108 if (jitter == 0) 109 return (max); 110 111 isc_random_get(&rnd); 112 return (max - rnd % jitter); 113} 114