/*	$OpenBSD: shuffle.c,v 1.4 2015/01/22 17:42:09 reyk Exp $	*/

/*
 * 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.
 */

/* based on: bind/lib/isc/shuffle.c,v 1.4 2008/07/09 17:07:32 reyk Exp $ */

#include <sys/types.h>

#include <stdlib.h>
#include <assert.h>

#include "relayd.h"

#define VALID_SHUFFLE(x)	(x != NULL)

void
shuffle_init(struct shuffle *shuffle)
{
	int i, i2;

	assert(VALID_SHUFFLE(shuffle));

	shuffle->isindex = 0;
	/* Initialize using a Knuth shuffle */
	for (i = 0; i < 65536; ++i) {
		i2 = arc4random_uniform(i + 1);
		shuffle->id_shuffle[i] = shuffle->id_shuffle[i2];
		shuffle->id_shuffle[i2] = i;
	}
}

u_int16_t
shuffle_generate16(struct shuffle *shuffle)
{
	u_int32_t si;
	u_int16_t r;
	int i, i2;

	assert(VALID_SHUFFLE(shuffle));

	do {
		si = arc4random();
		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);
}