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