net/batman-adv/bitarray.c

   1 /*
   2  * Copyright (C) 2006-2011 B.A.T.M.A.N. contributors:
   3  *
   4  * Simon Wunderlich, Marek Lindner
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of version 2 of the GNU General Public
   8  * License as published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  13  * General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  18  * 02110-1301, USA
  19  *
  20  */
  21
  22 #include "main.h"
  23 #include "bitarray.h"
  24
  25 #include <linux/bitops.h>
  26
  27 /* returns true if the corresponding bit in the given seq_bits indicates true
  28  * and curr_seqno is within range of last_seqno */
  29 int get_bit_status(const unsigned long *seq_bits, uint32_t last_seqno,
  30                    uint32_t curr_seqno)
  31 {
  32         int32_t diff, word_offset, word_num;
  33
  34         diff = last_seqno - curr_seqno;
  35         if (diff < 0 || diff >= TQ_LOCAL_WINDOW_SIZE) {
  36                 return 0;
  37         } else {
  38                 /* which word */
  39                 word_num = (last_seqno - curr_seqno) / WORD_BIT_SIZE;
  40                 /* which position in the selected word */
  41                 word_offset = (last_seqno - curr_seqno) % WORD_BIT_SIZE;
  42
  43                 if (test_bit(word_offset, &seq_bits[word_num]))
  44                         return 1;
  45                 else
  46                         return 0;
  47         }
  48 }
  49
  50 /* turn corresponding bit on, so we can remember that we got the packet */
  51 void bit_mark(unsigned long *seq_bits, int32_t n)
  52 {
  53         int32_t word_offset, word_num;
  54
  55         /* if too old, just drop it */
  56         if (n < 0 || n >= TQ_LOCAL_WINDOW_SIZE)
  57                 return;
  58
  59         /* which word */
  60         word_num = n / WORD_BIT_SIZE;
  61         /* which position in the selected word */
  62         word_offset = n % WORD_BIT_SIZE;
  63
  64         set_bit(word_offset, &seq_bits[word_num]); /* turn the position on */
  65 }
  66
  67 /* shift the packet array by n places. */
  68 static void bit_shift(unsigned long *seq_bits, int32_t n)
  69 {
  70         int32_t word_offset, word_num;
  71         int32_t i;
  72
  73         if (n <= 0 || n >= TQ_LOCAL_WINDOW_SIZE)
  74                 return;
  75
  76         word_offset = n % WORD_BIT_SIZE;/* shift how much inside each word */
  77         word_num = n / WORD_BIT_SIZE;   /* shift over how much (full) words */
  78
  79         for (i = NUM_WORDS - 1; i > word_num; i--) {
  80                 /* going from old to new, so we don't overwrite the data we copy
  81                  * from.
  82                  *
  83                  * left is high, right is low: FEDC BA98 7654 3210
  84                  *                                        ^^ ^^
  85                  *                             vvvv
  86                  * ^^^^ = from, vvvvv =to, we'd have word_num==1 and
  87                  * word_offset==WORD_BIT_SIZE/2 ????? in this example.
  88                  * (=24 bits)
  89                  *
  90                  * our desired output would be: 9876 5432 1000 0000
  91                  * */
  92
  93                 seq_bits[i] =
  94                         (seq_bits[i - word_num] << word_offset) +
  95                         /* take the lower port from the left half, shift it left
  96                          * to its final position */
  97                         (seq_bits[i - word_num - 1] >>
  98                          (WORD_BIT_SIZE-word_offset));
  99                 /* and the upper part of the right half and shift it left to
 100                  * it's position */
 101                 /* for our example that would be: word[0] = 9800 + 0076 =
 102                  * 9876 */
 103         }
 104         /* now for our last word, i==word_num, we only have the it's "left"
 105          * half. that's the 1000 word in our example.*/
 106
 107         seq_bits[i] = (seq_bits[i - word_num] << word_offset);
 108
 109         /* pad the rest with 0, if there is anything */
 110         i--;
 111
 112         for (; i >= 0; i--)
 113                 seq_bits[i] = 0;
 114 }
 115
 116 static void bit_reset_window(unsigned long *seq_bits)
 117 {
 118         int i;
 119         for (i = 0; i < NUM_WORDS; i++)
 120                 seq_bits[i] = 0;
 121 }
 122
 123
 124 /* receive and process one packet within the sequence number window.
 125  *
 126  * returns:
 127  *  1 if the window was moved (either new or very old)
 128  *  0 if the window was not moved/shifted.
 129  */
 130 int bit_get_packet(void *priv, unsigned long *seq_bits,
 131                     int32_t seq_num_diff, int set_mark)
 132 {
 133         struct bat_priv *bat_priv = priv;
 134
 135         /* sequence number is slightly older. We already got a sequence number
 136          * higher than this one, so we just mark it. */
 137
 138         if ((seq_num_diff <= 0) && (seq_num_diff > -TQ_LOCAL_WINDOW_SIZE)) {
 139                 if (set_mark)
 140                         bit_mark(seq_bits, -seq_num_diff);
 141                 return 0;
 142         }
 143
 144         /* sequence number is slightly newer, so we shift the window and
 145          * set the mark if required */
 146
 147         if ((seq_num_diff > 0) && (seq_num_diff < TQ_LOCAL_WINDOW_SIZE)) {
 148                 bit_shift(seq_bits, seq_num_diff);
 149
 150                 if (set_mark)
 151                         bit_mark(seq_bits, 0);
 152                 return 1;
 153         }
 154
 155         /* sequence number is much newer, probably missed a lot of packets */
 156
 157         if ((seq_num_diff >= TQ_LOCAL_WINDOW_SIZE)
 158                 || (seq_num_diff < EXPECTED_SEQNO_RANGE)) {
 159                 bat_dbg(DBG_BATMAN, bat_priv,
 160                         "We missed a lot of packets (%i) !\n",
 161                         seq_num_diff - 1);
 162                 bit_reset_window(seq_bits);
 163                 if (set_mark)
 164                         bit_mark(seq_bits, 0);
 165                 return 1;
 166         }
 167
 168         /* received a much older packet. The other host either restarted
 169          * or the old packet got delayed somewhere in the network. The
 170          * packet should be dropped without calling this function if the
 171          * seqno window is protected. */
 172
 173         if ((seq_num_diff <= -TQ_LOCAL_WINDOW_SIZE)
 174                 || (seq_num_diff >= EXPECTED_SEQNO_RANGE)) {
 175
 176                 bat_dbg(DBG_BATMAN, bat_priv,
 177                         "Other host probably restarted!\n");
 178
 179                 bit_reset_window(seq_bits);
 180                 if (set_mark)
 181                         bit_mark(seq_bits, 0);
 182
 183                 return 1;
 184         }
 185
 186         /* never reached */
 187         return 0;
 188 }
 189
 190 /* count the hamming weight, how many good packets did we receive? just count
 191  * the 1's.
 192  */
 193 int bit_packet_count(const unsigned long *seq_bits)
 194 {
 195         int i, hamming = 0;
 196
 197         for (i = 0; i < NUM_WORDS; i++)
 198                 hamming += hweight_long(seq_bits[i]);
 199
 200         return hamming;
 201 }