1 /*	$OpenBSD: shuffle.c,v 1.4 2015/01/22 17:42:09 reyk Exp $	*/
2 
3 /*
4  * Portions Copyright (C) 2008 Theo de Raadt
5  *
6  * Permission to use, copy, modify, and distribute this software for any
7  * purpose with or without fee is hereby granted, provided that the above
8  * copyright notice and this permission notice appear in all copies.
9  *
10  * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM
11  * DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
12  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
13  * INTERNET SOFTWARE CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
14  * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
15  * FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
16  * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
17  * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18  */
19 
20 /* based on: bind/lib/isc/shuffle.c,v 1.4 2008/07/09 17:07:32 reyk Exp $ */
21 
22 #include <sys/types.h>
23 
24 #include <stdlib.h>
25 #include <assert.h>
26 
27 #include "relayd.h"
28 
29 #define VALID_SHUFFLE(x)	(x != NULL)
30 
31 void
32 shuffle_init(struct shuffle *shuffle)
33 {
34 	int i, i2;
35 
36 	assert(VALID_SHUFFLE(shuffle));
37 
38 	shuffle->isindex = 0;
39 	/* Initialize using a Knuth shuffle */
40 	for (i = 0; i < 65536; ++i) {
41 		i2 = arc4random_uniform(i + 1);
42 		shuffle->id_shuffle[i] = shuffle->id_shuffle[i2];
43 		shuffle->id_shuffle[i2] = i;
44 	}
45 }
46 
47 u_int16_t
48 shuffle_generate16(struct shuffle *shuffle)
49 {
50 	u_int32_t si;
51 	u_int16_t r;
52 	int i, i2;
53 
54 	assert(VALID_SHUFFLE(shuffle));
55 
56 	do {
57 		si = arc4random();
58 		i = shuffle->isindex & 0xFFFF;
59 		i2 = (shuffle->isindex - (si & 0x7FFF)) & 0xFFFF;
60 		r = shuffle->id_shuffle[i];
61 		shuffle->id_shuffle[i] = shuffle->id_shuffle[i2];
62 		shuffle->id_shuffle[i2] = r;
63 		shuffle->isindex++;
64 	} while (r == 0);
65 
66 	return (r);
67 }