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 39 static isc_once_t once = ISC_ONCE_INIT; 40 41 static void 42 initialize_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 57 static void 58 initialize(void) 59 { 60 RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS); 61 } 62 63 void 64 isc_random_seed(isc_uint32_t seed) 65 { 66 initialize(); 67 68 #ifndef HAVE_ARC4RANDOM 69 srand(seed); 70 #endif 71 } 72 73 void 74 isc_random_get(isc_uint32_t *val) 75 { 76 REQUIRE(val != NULL); 77 78 initialize(); 79 80 #ifndef HAVE_ARC4RANDOM 81 /* 82 * rand()'s lower bits are not random. 83 * rand()'s upper bit is zero. 84 */ 85 #if RAND_MAX >= 0xfffff 86 /* We have at least 20 bits. Use lower 16 excluding lower most 4 */ 87 *val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000); 88 #elif RAND_MAX >= 0x7fff 89 /* We have at least 15 bits. Use lower 10/11 excluding lower most 4 */ 90 *val = ((rand() >> 4) & 0x000007ff) | ((rand() << 7) & 0x003ff800) | 91 ((rand() << 18) & 0xffc00000); 92 #else 93 #error RAND_MAX is too small 94 #endif 95 #else 96 *val = arc4random(); 97 #endif 98 } 99 100 isc_uint32_t 101 isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) { 102 isc_uint32_t rnd; 103 104 REQUIRE(jitter < max || (jitter == 0 && max == 0)); 105 106 if (jitter == 0) 107 return (max); 108 109 isc_random_get(&rnd); 110 return (max - rnd % jitter); 111 } 112