lib/isc/random.c

	random.c revision 1b5a72829324a0d2fa327a270caea8fd02ae8779
/*
 * Copyright (C) 1999-2001  Internet Software Consortium.
 *
 * 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 INTERNET SOFTWARE CONSORTIUM
 * DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
 * INTERNET SOFTWARE CONSORTIUM 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.
 */

/* $Id: random.c,v 1.18 2003/08/05 00:08:30 marka Exp $ */

#include <config.h>

#include <stdlib.h>
#include <time.h>       /* Required for time(). */

#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);
#else
    arc4random_addrandom((u_char *) &seed, sizeof(isc_uint32_t));
#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_jitter(isc_uint32_t max, isc_uint32_t jitter) {
    REQUIRE(jitter < max);
    if (jitter == 0)
        return (max);
    else
#ifndef HAVE_ARC4RANDOM
        return (max - rand() % jitter);
#else
        return (max - arc4random() % jitter);
#endif
}