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/*
* Copyright (C) 2004, 2005 Internet Systems Consortium, Inc. ("ISC")
* Copyright (C) 1999-2003 Internet Software Consortium.
* Copyright (C) 2008 Damien Miller
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
* OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
* PERFORMANCE OF THIS SOFTWARE.
*/
/* $ISC: random.c,v 1.21.18.2 2005/04/29 00:16:48 marka Exp $ */
/*! \file */
#include <config.h>
#include <stdlib.h>
#include <time.h> /* Required for time(). */
#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <isc/mutex.h>
#include <isc/once.h>
#include <isc/random.h>
#include <isc/string.h>
#include <isc/util.h>
static isc_once_t once = ISC_ONCE_INIT;
static void
initialize_rand(void)
{
#ifndef HAVE_ARC4RANDOM
unsigned int pid = getpid();
/*
* The low bits of pid generally change faster.
* Xor them with the high bits of time which change slowly.
*/
pid = ((pid << 16) & 0xffff0000) | ((pid >> 16) & 0xffff);
srand(time(NULL) ^ pid);
#endif
}
static void
initialize(void)
{
RUNTIME_CHECK(isc_once_do(&once, initialize_rand) == ISC_R_SUCCESS);
}
void
isc_random_seed(isc_uint32_t seed)
{
initialize();
#ifndef HAVE_ARC4RANDOM
srand(seed);
#endif
}
void
isc_random_get(isc_uint32_t *val)
{
REQUIRE(val != NULL);
initialize();
#ifndef HAVE_ARC4RANDOM
/*
* rand()'s lower bits are not random.
* rand()'s upper bit is zero.
*/
*val = ((rand() >> 4) & 0xffff) | ((rand() << 12) & 0xffff0000);
#else
*val = arc4random();
#endif
}
isc_uint32_t
isc_random_uniform(isc_uint32_t upper_bound)
{
isc_uint32_t r, min;
/*
* Uniformity is achieved by generating new random numbers until
* the one returned is outside the range [0, 2**32 % upper_bound).
* This guarantees the selected random number will be inside
* [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
* after reduction modulo upper_bound.
*/
if (upper_bound < 2)
return 0;
#if (ULONG_MAX > 0xffffffffUL)
min = 0x100000000UL % upper_bound;
#else
/* Calculate (2**32 % upper_bound) avoiding 64-bit math */
if (upper_bound > 0x80000000)
min = 1 + ~upper_bound; /* 2**32 - upper_bound */
else {
/* (2**32 - x) % x == 2**32 % x when x <= 2**31 */
min = ((0xffffffff - upper_bound) + 1) % upper_bound;
}
#endif
/*
* This could theoretically loop forever doing this, but each retry
* has p > 0.5 (worst case, usually far better) of selecting a
* number inside the range we need, so it should rarely need to
* re-roll.
*/
for (;;) {
isc_random_get(&r);
if (r >= min)
break;
}
return r % upper_bound;
}
isc_uint32_t
isc_random_jitter(isc_uint32_t max, isc_uint32_t jitter) {
REQUIRE(jitter < max);
if (jitter == 0)
return (max);
else
return max - isc_random_uniform(jitter);
}
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