summaryrefslogtreecommitdiff
path: root/net/batman-adv/bitarray.c
blob: 9bc63b209b3fd0987c31db60716d70f92cd9e7a5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
/*
 * Copyright (C) 2006-2011 B.A.T.M.A.N. contributors:
 *
 * Simon Wunderlich, Marek Lindner
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA
 *
 */

#include "main.h"
#include "bitarray.h"

#include <linux/bitops.h>

/* returns true if the corresponding bit in the given seq_bits indicates true
 * and curr_seqno is within range of last_seqno */
int get_bit_status(const unsigned long *seq_bits, uint32_t last_seqno,
		   uint32_t curr_seqno)
{
	int32_t diff, word_offset, word_num;

	diff = last_seqno - curr_seqno;
	if (diff < 0 || diff >= TQ_LOCAL_WINDOW_SIZE) {
		return 0;
	} else {
		/* which word */
		word_num = (last_seqno - curr_seqno) / WORD_BIT_SIZE;
		/* which position in the selected word */
		word_offset = (last_seqno - curr_seqno) % WORD_BIT_SIZE;

		if (test_bit(word_offset, &seq_bits[word_num]))
			return 1;
		else
			return 0;
	}
}

/* turn corresponding bit on, so we can remember that we got the packet */
void bit_mark(unsigned long *seq_bits, int32_t n)
{
	int32_t word_offset, word_num;

	/* if too old, just drop it */
	if (n < 0 || n >= TQ_LOCAL_WINDOW_SIZE)
		return;

	/* which word */
	word_num = n / WORD_BIT_SIZE;
	/* which position in the selected word */
	word_offset = n % WORD_BIT_SIZE;

	set_bit(word_offset, &seq_bits[word_num]); /* turn the position on */
}

/* shift the packet array by n places. */
static void bit_shift(unsigned long *seq_bits, int32_t n)
{
	int32_t word_offset, word_num;
	int32_t i;

	if (n <= 0 || n >= TQ_LOCAL_WINDOW_SIZE)
		return;

	word_offset = n % WORD_BIT_SIZE;/* shift how much inside each word */
	word_num = n / WORD_BIT_SIZE;	/* shift over how much (full) words */

	for (i = NUM_WORDS - 1; i > word_num; i--) {
		/* going from old to new, so we don't overwrite the data we copy
		 * from.
		 *
		 * left is high, right is low: FEDC BA98 7654 3210
		 *					  ^^ ^^
		 *			       vvvv
		 * ^^^^ = from, vvvvv =to, we'd have word_num==1 and
		 * word_offset==WORD_BIT_SIZE/2 ????? in this example.
		 * (=24 bits)
		 *
		 * our desired output would be: 9876 5432 1000 0000
		 * */

		seq_bits[i] =
			(seq_bits[i - word_num] << word_offset) +
			/* take the lower port from the left half, shift it left
			 * to its final position */
			(seq_bits[i - word_num - 1] >>
			 (WORD_BIT_SIZE-word_offset));
		/* and the upper part of the right half and shift it left to
		 * its position */
		/* for our example that would be: word[0] = 9800 + 0076 =
		 * 9876 */
	}
	/* now for our last word, i==word_num, we only have its "left" half.
	 * that's the 1000 word in our example.*/

	seq_bits[i] = (seq_bits[i - word_num] << word_offset);

	/* pad the rest with 0, if there is anything */
	i--;

	for (; i >= 0; i--)
		seq_bits[i] = 0;
}

static void bit_reset_window(unsigned long *seq_bits)
{
	int i;
	for (i = 0; i < NUM_WORDS; i++)
		seq_bits[i] = 0;
}


/* receive and process one packet within the sequence number window.
 *
 * returns:
 *  1 if the window was moved (either new or very old)
 *  0 if the window was not moved/shifted.
 */
int bit_get_packet(void *priv, unsigned long *seq_bits,
		    int32_t seq_num_diff, int set_mark)
{
	struct bat_priv *bat_priv = priv;

	/* sequence number is slightly older. We already got a sequence number
	 * higher than this one, so we just mark it. */

	if ((seq_num_diff <= 0) && (seq_num_diff > -TQ_LOCAL_WINDOW_SIZE)) {
		if (set_mark)
			bit_mark(seq_bits, -seq_num_diff);
		return 0;
	}

	/* sequence number is slightly newer, so we shift the window and
	 * set the mark if required */

	if ((seq_num_diff > 0) && (seq_num_diff < TQ_LOCAL_WINDOW_SIZE)) {
		bit_shift(seq_bits, seq_num_diff);

		if (set_mark)
			bit_mark(seq_bits, 0);
		return 1;
	}

	/* sequence number is much newer, probably missed a lot of packets */

	if ((seq_num_diff >= TQ_LOCAL_WINDOW_SIZE)
		&& (seq_num_diff < EXPECTED_SEQNO_RANGE)) {
		bat_dbg(DBG_BATMAN, bat_priv,
			"We missed a lot of packets (%i) !\n",
			seq_num_diff - 1);
		bit_reset_window(seq_bits);
		if (set_mark)
			bit_mark(seq_bits, 0);
		return 1;
	}

	/* received a much older packet. The other host either restarted
	 * or the old packet got delayed somewhere in the network. The
	 * packet should be dropped without calling this function if the
	 * seqno window is protected. */

	if ((seq_num_diff <= -TQ_LOCAL_WINDOW_SIZE)
		|| (seq_num_diff >= EXPECTED_SEQNO_RANGE)) {

		bat_dbg(DBG_BATMAN, bat_priv,
			"Other host probably restarted!\n");

		bit_reset_window(seq_bits);
		if (set_mark)
			bit_mark(seq_bits, 0);

		return 1;
	}

	/* never reached */
	return 0;
}

/* count the hamming weight, how many good packets did we receive? just count
 * the 1's.
 */
int bit_packet_count(const unsigned long *seq_bits)
{
	int i, hamming = 0;

	for (i = 0; i < NUM_WORDS; i++)
		hamming += hweight_long(seq_bits[i]);

	return hamming;
}