drivers/staging/batman-adv/bitarray.c

   1 /*
   2  * Copyright (C) 2006-2010 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 /* returns true if the corresponding bit in the given seq_bits indicates true
  26  * and curr_seqno is within range of last_seqno */
  27 uint8_t get_bit_status(TYPE_OF_WORD *seq_bits, uint32_t last_seqno,
  28                        uint32_t curr_seqno)
  29 {
  30         int32_t diff, word_offset, word_num;
  31
  32         diff = last_seqno - curr_seqno;
  33         if (diff < 0 || diff >= TQ_LOCAL_WINDOW_SIZE) {
  34                 return 0;
  35         } else {
  36                 /* which word */
  37                 word_num = (last_seqno - curr_seqno) / WORD_BIT_SIZE;
  38                 /* which position in the selected word */
  39                 word_offset = (last_seqno - curr_seqno) % WORD_BIT_SIZE;
  40
  41                 if (seq_bits[word_num] & 1 << word_offset)
  42                         return 1;
  43                 else
  44                         return 0;
  45         }
  46 }
  47
  48 /* turn corresponding bit on, so we can remember that we got the packet */
  49 void bit_mark(TYPE_OF_WORD *seq_bits, int32_t n)
  50 {
  51         int32_t word_offset, word_num;
  52
  53         /* if too old, just drop it */
  54         if (n < 0 || n >= TQ_LOCAL_WINDOW_SIZE)
  55                 return;
  56
  57         /* which word */
  58         word_num = n / WORD_BIT_SIZE;
  59         /* which position in the selected word */
  60         word_offset = n % WORD_BIT_SIZE;
  61
  62         seq_bits[word_num] |= 1 << word_offset; /* turn the position on */
  63 }
  64
  65 /* shift the packet array by n places. */
  66 static void bit_shift(TYPE_OF_WORD *seq_bits, int32_t n)
  67 {
  68         int32_t word_offset, word_num;
  69         int32_t i;
  70
  71         if (n <= 0 || n >= TQ_LOCAL_WINDOW_SIZE)
  72                 return;
  73
  74         word_offset = n % WORD_BIT_SIZE;/* shift how much inside each word */
  75         word_num = n / WORD_BIT_SIZE;   /* shift over how much (full) words */
  76
  77         for (i = NUM_WORDS - 1; i > word_num; i--) {
  78                 /* going from old to new, so we don't overwrite the data we copy
  79                  * from.
  80                  *
  81                  * left is high, right is low: FEDC BA98 7654 3210
  82                  *                                        ^^ ^^
  83                  *                             vvvv
  84                  * ^^^^ = from, vvvvv =to, we'd have word_num==1 and
  85                  * word_offset==WORD_BIT_SIZE/2 ????? in this example.
  86                  * (=24 bits)
  87                  *
  88                  * our desired output would be: 9876 5432 1000 0000
  89                  * */
  90
  91                 seq_bits[i] =
  92                         (seq_bits[i - word_num] << word_offset) +
  93                         /* take the lower port from the left half, shift it left
  94                          * to its final position */
  95                         (seq_bits[i - word_num - 1] >>
  96                          (WORD_BIT_SIZE-word_offset));
  97                 /* and the upper part of the right half and shift it left to
  98                  * it's position */
  99                 /* for our example that would be: word[0] = 9800 + 0076 =
 100                  * 9876 */
 101         }
 102         /* now for our last word, i==word_num, we only have the it's "left"
 103          * half. that's the 1000 word in our example.*/
 104
 105         seq_bits[i] = (seq_bits[i - word_num] << word_offset);
 106
 107         /* pad the rest with 0, if there is anything */
 108         i--;
 109
 110         for (; i >= 0; i--)
 111                 seq_bits[i] = 0;
 112 }
 113
 114 static void bit_reset_window(TYPE_OF_WORD *seq_bits)
 115 {
 116         int i;
 117         for (i = 0; i < NUM_WORDS; i++)
 118                 seq_bits[i] = 0;
 119 }
 120
 121
 122 /* receive and process one packet within the sequence number window.
 123  *
 124  * returns:
 125  *  1 if the window was moved (either new or very old)
 126  *  0 if the window was not moved/shifted.
 127  */
 128 char bit_get_packet(TYPE_OF_WORD *seq_bits, int32_t seq_num_diff,
 129                     int8_t set_mark)
 130 {
 131         /* sequence number is slightly older. We already got a sequence number
 132          * higher than this one, so we just mark it. */
 133
 134         if ((seq_num_diff <= 0) && (seq_num_diff > -TQ_LOCAL_WINDOW_SIZE)) {
 135                 if (set_mark)
 136                         bit_mark(seq_bits, -seq_num_diff);
 137                 return 0;
 138         }
 139
 140         /* sequence number is slightly newer, so we shift the window and
 141          * set the mark if required */
 142
 143         if ((seq_num_diff > 0) && (seq_num_diff < TQ_LOCAL_WINDOW_SIZE)) {
 144                 bit_shift(seq_bits, seq_num_diff);
 145
 146                 if (set_mark)
 147                         bit_mark(seq_bits, 0);
 148                 return 1;
 149         }
 150
 151         /* sequence number is much newer, probably missed a lot of packets */
 152
 153         if ((seq_num_diff >= TQ_LOCAL_WINDOW_SIZE)
 154                 || (seq_num_diff < EXPECTED_SEQNO_RANGE)) {
 155                 bat_dbg(DBG_BATMAN,
 156                         "We missed a lot of packets (%i) !\n",
 157                         seq_num_diff - 1);
 158                 bit_reset_window(seq_bits);
 159                 if (set_mark)
 160                         bit_mark(seq_bits, 0);
 161                 return 1;
 162         }
 163
 164         /* received a much older packet. The other host either restarted
 165          * or the old packet got delayed somewhere in the network. The
 166          * packet should be dropped without calling this function if the
 167          * seqno window is protected. */
 168
 169         if ((seq_num_diff <= -TQ_LOCAL_WINDOW_SIZE)
 170                 || (seq_num_diff >= EXPECTED_SEQNO_RANGE)) {
 171
 172                 bat_dbg(DBG_BATMAN,
 173                         "Other host probably restarted!\n");
 174
 175                 bit_reset_window(seq_bits);
 176                 if (set_mark)
 177                         bit_mark(seq_bits, 0);
 178
 179                 return 1;
 180         }
 181
 182         /* never reached */
 183         return 0;
 184 }
 185
 186 /* count the hamming weight, how many good packets did we receive? just count
 187  * the 1's. The inner loop uses the Kernighan algorithm, see
 188  * http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan
 189  */
 190 int bit_packet_count(TYPE_OF_WORD *seq_bits)
 191 {
 192         int i, hamming = 0;
 193         TYPE_OF_WORD word;
 194
 195         for (i = 0; i < NUM_WORDS; i++) {
 196                 word = seq_bits[i];
 197
 198                 while (word) {
 199                         word &= word-1;
 200                         hamming++;
 201                 }
 202         }
 203         return hamming;
 204 }