/*
 * 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;
}