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/*
* Portions Copyright (C) 2008 Theo de Raadt
*
* 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.
*/
/* $OpenBSD: shuffle.c,v 1.1 2008/02/29 12:21:12 deraadt Exp $ */
#include <config.h>
#include <stdlib.h>
#include <isc/shuffle.h>
#include <isc/random.h>
#include <isc/time.h>
#include <isc/util.h>
#define VALID_SHUFFLE(x) (x != NULL)
void
isc_shuffle_init(isc_shuffle_t *shuffle)
{
isc_uint32_t si;
isc_uint16_t r;
int i, i2;
REQUIRE(VALID_SHUFFLE(shuffle));
shuffle->isindex = 0;
for (i = 0; i < 65536; ++i)
shuffle->id_shuffle[i] = i;
/* Initialize using a Durstenfeld shuffle */
for (i = 65536; --i; ) {
isc_random_get(&si);
/* disregard the modulo bias because it is small */
i2 = (si % (i + 1)) & 0xffff;
r = shuffle->id_shuffle[i];
shuffle->id_shuffle[i] = shuffle->id_shuffle[i2];
shuffle->id_shuffle[i2] = r;
}
}
isc_uint16_t
isc_shuffle_generate16(isc_shuffle_t *shuffle)
{
isc_uint32_t si;
isc_uint16_t r;
int i, i2;
REQUIRE(VALID_SHUFFLE(shuffle));
do {
isc_random_get(&si);
i = shuffle->isindex & 0xFFFF;
i2 = (shuffle->isindex - (si & 0x7FFF)) & 0xFFFF;
r = shuffle->id_shuffle[i];
shuffle->id_shuffle[i] = shuffle->id_shuffle[i2];
shuffle->id_shuffle[i2] = r;
shuffle->isindex++;
} while (r == 0);
return (r);
}
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