/contrib/bind9/lib/isc/random.c

  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}