2 * Copyright (C) 2004, 2005, 2007, 2009, 2013, 2014 Internet Systems Consortium, Inc. ("ISC")
3 * Copyright (C) 1999-2003 Internet Software Consortium.
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.
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.
18 /* $Id: random.c,v 1.28 2009/07/16 05:52:46 marka Exp $ */
25 #include <time.h> /* Required for time(). */
26 #ifdef HAVE_SYS_TYPES_H
27 #include <sys/types.h>
33 #include <isc/mutex.h>
35 #include <isc/random.h>
36 #include <isc/string.h>
39 static isc_once_t once = ISC_ONCE_INIT;
44 #ifndef HAVE_ARC4RANDOM
45 unsigned int pid = getpid();
48 * The low bits of pid generally change faster.
49 * Xor them with the high bits of time which change slowly.
51 pid = ((pid << 16) & 0xffff0000) | ((pid >> 16) & 0xffff);
53 srand((unsigned)time(NULL) ^ pid);
60 RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS);
64 isc_random_seed(isc_uint32_t seed)
68 #ifndef HAVE_ARC4RANDOM
70 #elif defined(HAVE_ARC4RANDOM_ADDRANDOM)
71 arc4random_addrandom((u_char *) &seed, sizeof(isc_uint32_t));
74 * If arcrandom() is available and no corresponding seeding
75 * function arc4random_addrandom() is available, no seeding is
76 * done on such platforms (e.g., OpenBSD 5.5). This is because
77 * the OS itself is supposed to seed the RNG and it is assumed
78 * that no explicit seeding is required.
84 isc_random_get(isc_uint32_t *val)
90 #ifndef HAVE_ARC4RANDOM
92 * rand()'s lower bits are not random.
93 * rand()'s upper bit is zero.
95 #if RAND_MAX >= 0xfffff
96 /* We have at least 20 bits. Use lower 16 excluding lower most 4 */
97 *val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000);
98 #elif RAND_MAX >= 0x7fff
99 /* We have at least 15 bits. Use lower 10/11 excluding lower most 4 */
100 *val = ((rand() >> 4) & 0x000007ff) | ((rand() << 7) & 0x003ff800) |
101 ((rand() << 18) & 0xffc00000);
103 #error RAND_MAX is too small
111 isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) {
114 REQUIRE(jitter < max || (jitter == 0 && max == 0));
119 isc_random_get(&rnd);
120 return (max - rnd % jitter);