/* SCTP kernel reference Implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 * Copyright (c) 2001 Intel Corp.
 *
 * This file is part of the SCTP kernel reference Implementation
 *
 * These functions manipulate sctp tsn mapping array.
 *
 * The SCTP reference implementation is free software;
 * you can redistribute it and/or modify it under the terms of
 * the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * The SCTP reference implementation 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 GNU CC; see the file COPYING.  If not, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <lksctp-developers@lists.sourceforge.net>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <piggy@acm.org>
 *    Jon Grimm             <jgrimm@us.ibm.com>
 *    Karl Knutson          <karl@athena.chicago.il.us>
 *    Sridhar Samudrala     <sri@us.ibm.com>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#include <linux/types.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>

static void sctp_tsnmap_update(struct sctp_tsnmap *map);
static void sctp_tsnmap_find_gap_ack(__u8 *map, __u16 off,
                                     __u16 len, __u16 base,
                                     int *started, __u16 *start,
                                     int *ended, __u16 *end);

/* Initialize a block of memory as a tsnmap.  */
struct sctp_tsnmap *sctp_tsnmap_init(struct sctp_tsnmap *map, __u16 len,
                                     __u32 initial_tsn)
{
        map->tsn_map = map->raw_map;
        map->overflow_map = map->tsn_map + len;
        map->len = len;

        /* Clear out a TSN ack status.  */
        memset(map->tsn_map, 0x00, map->len + map->len);

        /* Keep track of TSNs represented by tsn_map.  */
        map->base_tsn = initial_tsn;
        map->overflow_tsn = initial_tsn + map->len;
        map->cumulative_tsn_ack_point = initial_tsn - 1;
        map->max_tsn_seen = map->cumulative_tsn_ack_point;
        map->malloced = 0;
        map->num_dup_tsns = 0;

        return map;
}

/* Test the tracking state of this TSN.
 * Returns:
 *   0 if the TSN has not yet been seen
 *  >0 if the TSN has been seen (duplicate)
 *  <0 if the TSN is invalid (too large to track)
 */
int sctp_tsnmap_check(const struct sctp_tsnmap *map, __u32 tsn)
{
        __s32 gap;
        int dup;

        /* Calculate the index into the mapping arrays.  */
        gap = tsn - map->base_tsn;

        /* Verify that we can hold this TSN.  */
        if (gap >= (/* base */ map->len + /* overflow */ map->len)) {
                dup = -1;
                goto out;
        }

        /* Honk if we've already seen this TSN.
         * We have three cases:
         *      1. The TSN is ancient or belongs to a previous tsn_map.
         *      2. The TSN is already marked in the tsn_map.
         *      3. The TSN is already marked in the tsn_map_overflow.
         */
        if (gap < 0 ||
            (gap < map->len && map->tsn_map[gap]) ||
            (gap >= map->len && map->overflow_map[gap - map->len]))
                dup = 1;
        else
                dup = 0;

out:
        return dup;
}


/* Mark this TSN as seen.  */
void sctp_tsnmap_mark(struct sctp_tsnmap *map, __u32 tsn)
{
        __s32 gap;

        /* Vacuously mark any TSN which precedes the map base or
         * exceeds the end of the map.
         */
        if (TSN_lt(tsn, map->base_tsn))
                return;
        if (!TSN_lt(tsn, map->base_tsn + map->len + map->len))
                return;

        /* Bump the max.  */
        if (TSN_lt(map->max_tsn_seen, tsn))
                map->max_tsn_seen = tsn;

        /* Assert: TSN is in range.  */
        gap = tsn - map->base_tsn;

        /* Mark the TSN as received.  */
        if (gap < map->len)
                map->tsn_map[gap]++;
        else
                map->overflow_map[gap - map->len]++;

        /* Go fixup any internal TSN mapping variables including
         * cumulative_tsn_ack_point.
         */
        sctp_tsnmap_update(map);
}


/* Initialize a Gap Ack Block iterator from memory being provided.  */
SCTP_STATIC void sctp_tsnmap_iter_init(const struct sctp_tsnmap *map,
                                       struct sctp_tsnmap_iter *iter)
{
        /* Only start looking one past the Cumulative TSN Ack Point.  */
        iter->start = map->cumulative_tsn_ack_point + 1;
}

/* Get the next Gap Ack Blocks. Returns 0 if there was not another block
 * to get.
 */
SCTP_STATIC int sctp_tsnmap_next_gap_ack(const struct sctp_tsnmap *map,
                                         struct sctp_tsnmap_iter *iter,
                                         __u16 *start, __u16 *end)
{
        int started, ended;
        __u16 start_, end_, offset;

        /* We haven't found a gap yet.  */
        started = ended = 0;

        /* If there are no more gap acks possible, get out fast.  */
        if (TSN_lte(map->max_tsn_seen, iter->start))
                return 0;

        /* Search the first mapping array.  */
        if (iter->start - map->base_tsn < map->len) {

                offset = iter->start - map->base_tsn;
                sctp_tsnmap_find_gap_ack(map->tsn_map, offset, map->len, 0,
                                         &started, &start_, &ended, &end_);
        }

        /* Do we need to check the overflow map? */
        if (!ended) {
                /* Fix up where we'd like to start searching in the
                 * overflow map.
                 */
                if (iter->start - map->base_tsn < map->len)
                        offset = 0;
                else
                        offset = iter->start - map->base_tsn - map->len;

                /* Search the overflow map.  */
                sctp_tsnmap_find_gap_ack(map->overflow_map,
                                         offset,
                                         map->len,
                                         map->len,
                                         &started, &start_,
                                         &ended, &end_);
        }

        /* The Gap Ack Block happens to end at the end of the
         * overflow map.
         */
        if (started && !ended) {
                ended++;
                end_ = map->len + map->len - 1;
        }

        /* If we found a Gap Ack Block, return the start and end and
         * bump the iterator forward.
         */
        if (ended) {
                /* Fix up the start and end based on the
                 * Cumulative TSN Ack offset into the map.
                 */
                int gap = map->cumulative_tsn_ack_point -
                        map->base_tsn;

                *start = start_ - gap;
                *end = end_ - gap;

                /* Move the iterator forward.  */
                iter->start = map->cumulative_tsn_ack_point + *end + 1;
        }

        return ended;
}

/* Mark this and any lower TSN as seen.  */
void sctp_tsnmap_skip(struct sctp_tsnmap *map, __u32 tsn)
{
        __s32 gap;

        /* Vacuously mark any TSN which precedes the map base or
         * exceeds the end of the map.
         */
        if (TSN_lt(tsn, map->base_tsn))
                return;
        if (!TSN_lt(tsn, map->base_tsn + map->len + map->len))
                return;

        /* Bump the max.  */
        if (TSN_lt(map->max_tsn_seen, tsn))
                map->max_tsn_seen = tsn;

        /* Assert: TSN is in range.  */
        gap = tsn - map->base_tsn + 1;

        /* Mark the TSNs as received.  */
        if (gap <= map->len)
                memset(map->tsn_map, 0x01, gap);
        else {
                memset(map->tsn_map, 0x01, map->len);
                memset(map->overflow_map, 0x01, (gap - map->len));
        }

        /* Go fixup any internal TSN mapping variables including
         * cumulative_tsn_ack_point.
         */
        sctp_tsnmap_update(map);
}

/********************************************************************
 * 2nd Level Abstractions
 ********************************************************************/

/* This private helper function updates the tsnmap buffers and
 * the Cumulative TSN Ack Point.
 */
static void sctp_tsnmap_update(struct sctp_tsnmap *map)
{
        __u32 ctsn;

        ctsn = map->cumulative_tsn_ack_point;
        do {
                ctsn++;
                if (ctsn == map->overflow_tsn) {
                        /* Now tsn_map must have been all '1's,
                         * so we swap the map and check the overflow table
                         */
                        __u8 *tmp = map->tsn_map;
                        memset(tmp, 0, map->len);
                        map->tsn_map = map->overflow_map;
                        map->overflow_map = tmp;

                        /* Update the tsn_map boundaries.  */
                        map->base_tsn += map->len;
                        map->overflow_tsn += map->len;
                }
        } while (map->tsn_map[ctsn - map->base_tsn]);

        map->cumulative_tsn_ack_point = ctsn - 1; /* Back up one. */
}

/* How many data chunks  are we missing from our peer?
 */
__u16 sctp_tsnmap_pending(struct sctp_tsnmap *map)
{
        __u32 cum_tsn = map->cumulative_tsn_ack_point;
        __u32 max_tsn = map->max_tsn_seen;
        __u32 base_tsn = map->base_tsn;
        __u16 pending_data;
        __s32 gap, start, end, i;

        pending_data = max_tsn - cum_tsn;
        gap = max_tsn - base_tsn;

        if (gap <= 0 || gap >= (map->len + map->len))
                goto out;

        start = ((cum_tsn >= base_tsn) ? (cum_tsn - base_tsn + 1) : 0);
        end = ((gap > map->len ) ? map->len : gap + 1);

        for (i = start; i < end; i++) {
                if (map->tsn_map[i])
                        pending_data--;
        }

        if (gap >= map->len) {
                start = 0;
                end = gap - map->len + 1;
                for (i = start; i < end; i++) {
                        if (map->overflow_map[i])
                                pending_data--;
                }
        }

out:
        return pending_data;
}

/* This is a private helper for finding Gap Ack Blocks.  It searches a
 * single array for the start and end of a Gap Ack Block.
 *
 * The flags "started" and "ended" tell is if we found the beginning
 * or (respectively) the end of a Gap Ack Block.
 */
static void sctp_tsnmap_find_gap_ack(__u8 *map, __u16 off,
                                     __u16 len, __u16 base,
                                     int *started, __u16 *start,
                                     int *ended, __u16 *end)
{
        int i = off;

        /* Look through the entire array, but break out
         * early if we have found the end of the Gap Ack Block.
         */

        /* Also, stop looking past the maximum TSN seen. */

        /* Look for the start. */
        if (!(*started)) {
                for (; i < len; i++) {
                        if (map[i]) {
                                (*started)++;
                                *start = base + i;
                                break;
                        }
                }
        }

        /* Look for the end.  */
        if (*started) {
                /* We have found the start, let's find the
                 * end.  If we find the end, break out.
                 */
                for (; i < len; i++) {
                        if (!map[i]) {
                                (*ended)++;
                                *end = base + i - 1;
                                break;
                        }
                }
        }
}

/* Renege that we have seen a TSN.  */
void sctp_tsnmap_renege(struct sctp_tsnmap *map, __u32 tsn)
{
        __s32 gap;

        if (TSN_lt(tsn, map->base_tsn))
                return;
        if (!TSN_lt(tsn, map->base_tsn + map->len + map->len))
                return;

        /* Assert: TSN is in range.  */
        gap = tsn - map->base_tsn;

        /* Pretend we never saw the TSN.  */
        if (gap < map->len)
                map->tsn_map[gap] = 0;
        else
                map->overflow_map[gap - map->len] = 0;
}

/* How many gap ack blocks do we have recorded? */
__u16 sctp_tsnmap_num_gabs(struct sctp_tsnmap *map)
{
        struct sctp_tsnmap_iter iter;
        int gabs = 0;

        /* Refresh the gap ack information. */
        if (sctp_tsnmap_has_gap(map)) {
                __u16 start, end;
                sctp_tsnmap_iter_init(map, &iter);
                while (sctp_tsnmap_next_gap_ack(map, &iter,
                                                &start,
                                                &end)) {

                        map->gabs[gabs].start = htons(start);
                        map->gabs[gabs].end = htons(end);
                        gabs++;
                        if (gabs >= SCTP_MAX_GABS)
                                break;
                }
        }
        return gabs;
}