drivers/staging/batman-adv/bitarray.c

   1 /*
   2  * Copyright (C) 2006-2009 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 #include "log.h"
  25
  26 /* returns true if the corresponding bit in the given seq_bits indicates true
  27  * and curr_seqno is within range of last_seqno */
  28 uint8_t get_bit_status(TYPE_OF_WORD *seq_bits, uint16_t last_seqno,
  29                        uint16_t curr_seqno)
  30 {
  31         int16_t diff, word_offset, word_num;
  32
  33         diff = last_seqno - curr_seqno;
  34         if (diff < 0 || diff >= TQ_LOCAL_WINDOW_SIZE) {
  35                 return 0;
  36         } else {
  37                 /* which word */
  38                 word_num = (last_seqno - curr_seqno) / WORD_BIT_SIZE;
  39                 /* which position in the selected word */
  40                 word_offset = (last_seqno - curr_seqno) % WORD_BIT_SIZE;
  41
  42                 if (seq_bits[word_num] & 1 << word_offset)
  43                         return 1;
  44                 else
  45                         return 0;
  46         }
  47 }
  48
  49 /* turn corresponding bit on, so we can remember that we got the packet */
  50 void bit_mark(TYPE_OF_WORD *seq_bits, int32_t n)
  51 {
  52         int32_t word_offset, word_num;
  53
  54         /* if too old, just drop it */
  55         if (n < 0 || n >= TQ_LOCAL_WINDOW_SIZE)
  56                 return;
  57
  58         /* which word */
  59         word_num = n / WORD_BIT_SIZE;
  60         /* which position in the selected word */
  61         word_offset = n % WORD_BIT_SIZE;
  62
  63         seq_bits[word_num] |= 1 << word_offset; /* turn the position on */
  64 }
  65
  66 /* shift the packet array by n places. */
  67 void bit_shift(TYPE_OF_WORD *seq_bits, int32_t n)
  68 {
  69         int32_t word_offset, word_num;
  70         int32_t i;
  71
  72         if (n <= 0)
  73                 return;
  74
  75         word_offset = n % WORD_BIT_SIZE;/* shift how much inside each word */
  76         word_num = n / WORD_BIT_SIZE;   /* shift over how much (full) words */
  77
  78         for (i = NUM_WORDS - 1; i > word_num; i--) {
  79                 /* going from old to new, so we don't overwrite the data we copy
  80                  * from.
  81                  *
  82                  * left is high, right is low: FEDC BA98 7654 3210
  83                  *                                        ^^ ^^
  84                  *                             vvvv
  85                  * ^^^^ = from, vvvvv =to, we'd have word_num==1 and
  86                  * word_offset==WORD_BIT_SIZE/2 ????? in this example.
  87                  * (=24 bits)
  88                  *
  89                  * our desired output would be: 9876 5432 1000 0000
  90                  * */
  91
  92                 seq_bits[i] =
  93                         (seq_bits[i - word_num] << word_offset) +
  94                         /* take the lower port from the left half, shift it left
  95                          * to its final position */
  96                         (seq_bits[i - word_num - 1] >>
  97                          (WORD_BIT_SIZE-word_offset));
  98                 /* and the upper part of the right half and shift it left to
  99                  * it's position */
 100                 /* for our example that would be: word[0] = 9800 + 0076 =
 101                  * 9876 */
 102         }
 103         /* now for our last word, i==word_num, we only have the it's "left"
 104          * half. that's the 1000 word in our example.*/
 105
 106         seq_bits[i] = (seq_bits[i - word_num] << word_offset);
 107
 108         /* pad the rest with 0, if there is anything */
 109         i--;
 110
 111         for (; i >= 0; i--)
 112                 seq_bits[i] = 0;
 113 }
 114
 115
 116 /* receive and process one packet, returns 1 if received seq_num is considered
 117  * new, 0 if old  */
 118 char bit_get_packet(TYPE_OF_WORD *seq_bits, int16_t seq_num_diff,
 119                     int8_t set_mark)
 120 {
 121         int i;
 122
 123         /* we already got a sequence number higher than this one, so we just
 124          * mark it. this should wrap around the integer just fine */
 125         if ((seq_num_diff < 0) && (seq_num_diff >= -TQ_LOCAL_WINDOW_SIZE)) {
 126                 if (set_mark)
 127                         bit_mark(seq_bits, -seq_num_diff);
 128                 return 0;
 129         }
 130
 131         /* it seems we missed a lot of packets or the other host restarted */
 132         if ((seq_num_diff > TQ_LOCAL_WINDOW_SIZE) ||
 133             (seq_num_diff < -TQ_LOCAL_WINDOW_SIZE)) {
 134
 135                 if (seq_num_diff > TQ_LOCAL_WINDOW_SIZE)
 136                         debug_log(LOG_TYPE_BATMAN,
 137                                   "We missed a lot of packets (%i) !\n",
 138                                   seq_num_diff-1);
 139
 140                 if (-seq_num_diff > TQ_LOCAL_WINDOW_SIZE)
 141                         debug_log(LOG_TYPE_BATMAN,
 142                                   "Other host probably restarted !\n");
 143
 144                 for (i = 0; i < NUM_WORDS; i++)
 145                         seq_bits[i] = 0;
 146
 147                 if (set_mark)
 148                         seq_bits[0] = 1;  /* we only have the latest packet */
 149         } else {
 150                 bit_shift(seq_bits, seq_num_diff);
 151
 152                 if (set_mark)
 153                         bit_mark(seq_bits, 0);
 154         }
 155
 156         return 1;
 157 }
 158
 159 /* count the hamming weight, how many good packets did we receive? just count
 160  * the 1's. The inner loop uses the Kernighan algorithm, see
 161  * http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan
 162  */
 163 int bit_packet_count(TYPE_OF_WORD *seq_bits)
 164 {
 165         int i, hamming = 0;
 166         TYPE_OF_WORD word;
 167
 168         for (i = 0; i < NUM_WORDS; i++) {
 169                 word = seq_bits[i];
 170
 171                 while (word) {
 172                         word &= word-1;
 173                         hamming++;
 174                 }
 175         }
 176         return hamming;
 177 }