1 /* $NetBSD: random.c,v 1.5 2014/12/10 04:37:59 christos Exp $ */ 2 3 /* 4 * Copyright (C) 2004, 2005, 2007, 2009, 2013, 2014 Internet Systems Consortium, Inc. ("ISC") 5 * Copyright (C) 1999-2003 Internet Software Consortium. 6 * 7 * Permission to use, copy, modify, and/or distribute this software for any 8 * purpose with or without fee is hereby granted, provided that the above 9 * copyright notice and this permission notice appear in all copies. 10 * 11 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH 12 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY 13 * AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, 14 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM 15 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE 16 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR 17 * PERFORMANCE OF THIS SOFTWARE. 18 */ 19 20 /* Id: random.c,v 1.28 2009/07/16 05:52:46 marka Exp */ 21 22 /*! \file */ 23 24 #include <config.h> 25 26 #include <stdlib.h> 27 #include <time.h> /* Required for time(). */ 28 #ifdef HAVE_SYS_TYPES_H 29 #include <sys/types.h> 30 #endif 31 #ifdef HAVE_UNISTD_H 32 #include <unistd.h> 33 #endif 34 35 #include <isc/mutex.h> 36 #include <isc/once.h> 37 #include <isc/random.h> 38 #include <isc/string.h> 39 #include <isc/util.h> 40 41 static isc_once_t once = ISC_ONCE_INIT; 42 43 static void 44 initialize_rand(void) 45 { 46 #ifndef HAVE_ARC4RANDOM 47 unsigned int pid = getpid(); 48 49 /* 50 * The low bits of pid generally change faster. 51 * Xor them with the high bits of time which change slowly. 52 */ 53 pid = ((pid << 16) & 0xffff0000) | ((pid >> 16) & 0xffff); 54 55 srand((unsigned)time(NULL) ^ pid); 56 #endif 57 } 58 59 static void 60 initialize(void) 61 { 62 RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS); 63 } 64 65 void 66 isc_random_seed(isc_uint32_t seed) 67 { 68 initialize(); 69 70 #ifndef HAVE_ARC4RANDOM 71 srand(seed); 72 #elif defined(HAVE_ARC4RANDOM_ADDRANDOM) 73 arc4random_addrandom((u_char *) &seed, sizeof(isc_uint32_t)); 74 #else 75 /* 76 * If arcrandom() is available and no corresponding seeding 77 * function arc4random_addrandom() is available, no seeding is 78 * done on such platforms (e.g., OpenBSD 5.5). This is because 79 * the OS itself is supposed to seed the RNG and it is assumed 80 * that no explicit seeding is required. 81 */ 82 #endif 83 } 84 85 void 86 isc_random_get(isc_uint32_t *val) 87 { 88 REQUIRE(val != NULL); 89 90 initialize(); 91 92 #ifndef HAVE_ARC4RANDOM 93 /* 94 * rand()'s lower bits are not random. 95 * rand()'s upper bit is zero. 96 */ 97 #if RAND_MAX >= 0xfffff 98 /* We have at least 20 bits. Use lower 16 excluding lower most 4 */ 99 *val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000); 100 #elif RAND_MAX >= 0x7fff 101 /* We have at least 15 bits. Use lower 10/11 excluding lower most 4 */ 102 *val = ((rand() >> 4) & 0x000007ff) | ((rand() << 7) & 0x003ff800) | 103 ((rand() << 18) & 0xffc00000); 104 #else 105 #error RAND_MAX is too small 106 #endif 107 #else 108 *val = arc4random(); 109 #endif 110 } 111 112 isc_uint32_t 113 isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) { 114 isc_uint32_t rnd; 115 116 REQUIRE(jitter < max || (jitter == 0 && max == 0)); 117 118 if (jitter == 0) 119 return (max); 120 121 isc_random_get(&rnd); 122 return (max - rnd % jitter); 123 } 124