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/*
* Copyright (C) 2006-2009 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"
/* returns true if the corresponding bit in the given seq_bits indicates true
* and curr_seqno is within range of last_seqno */
uint8_t get_bit_status(TYPE_OF_WORD *seq_bits, uint16_t last_seqno,
uint16_t curr_seqno)
{
int16_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 (seq_bits[word_num] & 1 << word_offset)
return 1;
else
return 0;
}
}
/* turn corresponding bit on, so we can remember that we got the packet */
void bit_mark(TYPE_OF_WORD *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;
seq_bits[word_num] |= 1 << word_offset; /* turn the position on */
}
/* shift the packet array by n places. */
void bit_shift(TYPE_OF_WORD *seq_bits, int32_t n)
{
int32_t word_offset, word_num;
int32_t i;
if (n <= 0)
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
* it's position */
/* for our example that would be: word[0] = 9800 + 0076 =
* 9876 */
}
/* now for our last word, i==word_num, we only have the it's "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;
}
/* receive and process one packet, returns 1 if received seq_num is considered
* new, 0 if old */
char bit_get_packet(TYPE_OF_WORD *seq_bits, int16_t seq_num_diff,
int8_t set_mark)
{
int i;
/* we already got a sequence number higher than this one, so we just
* mark it. this should wrap around the integer just fine */
if ((seq_num_diff < 0) && (seq_num_diff >= -TQ_LOCAL_WINDOW_SIZE)) {
if (set_mark)
bit_mark(seq_bits, -seq_num_diff);
return 0;
}
/* it seems we missed a lot of packets or the other host restarted */
if ((seq_num_diff > TQ_LOCAL_WINDOW_SIZE) ||
(seq_num_diff < -TQ_LOCAL_WINDOW_SIZE)) {
if (seq_num_diff > TQ_LOCAL_WINDOW_SIZE)
bat_dbg(DBG_BATMAN,
"We missed a lot of packets (%i) !\n",
seq_num_diff-1);
if (-seq_num_diff > TQ_LOCAL_WINDOW_SIZE)
bat_dbg(DBG_BATMAN,
"Other host probably restarted !\n");
for (i = 0; i < NUM_WORDS; i++)
seq_bits[i] = 0;
if (set_mark)
seq_bits[0] = 1; /* we only have the latest packet */
} else {
bit_shift(seq_bits, seq_num_diff);
if (set_mark)
bit_mark(seq_bits, 0);
}
return 1;
}
/* count the hamming weight, how many good packets did we receive? just count
* the 1's. The inner loop uses the Kernighan algorithm, see
* http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan
*/
int bit_packet_count(TYPE_OF_WORD *seq_bits)
{
int i, hamming = 0;
TYPE_OF_WORD word;
for (i = 0; i < NUM_WORDS; i++) {
word = seq_bits[i];
while (word) {
word &= word-1;
hamming++;
}
}
return hamming;
}
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