/*

 * Copyright (c) 2006 Konstantin Shishkov

 * Copyright (c) 2007 Loren Merritt

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * FFmpeg 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

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with FFmpeg; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

 */

/**

 * @file

 * huffman tree builder and VLC generator

 */

#include <stdint.h>

#include "libavutil/error.h"

#include "libavutil/log.h"

#include "libavutil/macros.h"

#include "libavutil/mem.h"

#include "libavutil/qsort.h"

#include "huffman.h"

#include "vlc.h"

/* symbol for Huffman tree node */

#define HNODE -1

typedef struct HeapElem {

    union {

        uint64_t val;

        uint16_t dummy; // exists solely to ensure alignof(HeapElem) >= alignof(uint16_t)

    };

    int name;

} HeapElem;

static void heap_sift(HeapElem *h, int root, int size)

{

    while (root * 2 + 1 < size) {

        int child = root * 2 + 1;

        if (child < size - 1 && h[child].val > h[child+1].val)

            child++;

        if (h[root].val > h[child].val) {

            FFSWAP(HeapElem, h[root], h[child]);

            root = child;

        } else

            break;

    }

}

int ff_huff_gen_len_table(uint8_t *dst, const uint64_t *stats, int stats_size, int skip0)

{

    int *up;

    uint16_t *map;

    uint8_t *len;

    HeapElem *h = av_malloc_array(stats_size,

                                  sizeof(*h) + 2 * sizeof(up) + 2 * sizeof(len) + sizeof(map));

    if (!h)

        return AVERROR(ENOMEM);

    up  = (int*)(h + stats_size);

    // map is suitably aligned because up uses an even number of elements

    // and alignof(uint16_t) is either 1 or 2.

    map = (uint16_t*)(up + 2 * stats_size);

    len = (uint8_t*)(map + stats_size);

    int offset, i, next;

    int size = 0;

    int ret = 0;

    for (i = 0; i<stats_size; i++) {

        dst[i] = 255;

        if (stats[i] || !skip0)

            map[size++] = i;

    }

    for (offset = 1; ; offset <<= 1) {

        for (i=0; i < size; i++) {

            h[i].name = i;

            h[i].val = (stats[map[i]] << 14) + offset;

        }

        for (i = size / 2 - 1; i >= 0; i--)

            heap_sift(h, i, size);

        for (next = size; next < size * 2 - 1; next++) {

            // merge the two smallest entries, and put it back in the heap

            uint64_t min1v = h[0].val;

            up[h[0].name] = next;

            h[0].val = INT64_MAX;

            heap_sift(h, 0, size);

            up[h[0].name] = next;

            h[0].name = next;

            h[0].val += min1v;

            heap_sift(h, 0, size);

        }

        len[2 * size - 2] = 0;

        for (i = 2 * size - 3; i >= size; i--)

            len[i] = len[up[i]] + 1;

        for (i = 0; i < size; i++) {

            dst[map[i]] = len[up[i]] + 1;

            if (dst[map[i]] >= 32) break;

        }

        if (i==size) break;

    }

    av_free(h);

    return ret;

}

static void get_tree_codes(int8_t *lens, uint8_t *xlat,

                           Node *nodes, int node, int pl, int *pos, int no_zero_count)

{

    int s;

    s = nodes[node].sym;

    if (s != HNODE || (no_zero_count && !nodes[node].count)) {

        lens[*pos] = pl;

        xlat[*pos] = s;

        (*pos)++;

    } else {

        pl++;

        get_tree_codes(lens, xlat, nodes, nodes[node].n0, pl,

                       pos, no_zero_count);

        get_tree_codes(lens, xlat, nodes, nodes[node].n0 + 1, pl,

                       pos, no_zero_count);

    }

}

static int build_huff_tree(VLC *vlc, Node *nodes, int head, int flags, int nb_bits, void *logctx)

{

    int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);

    int8_t lens[256];

    uint8_t xlat[256];

    int pos = 0;

    get_tree_codes(lens, xlat, nodes, head, 0,

                   &pos, no_zero_count);

    return ff_vlc_init_from_lengths(vlc, nb_bits, pos, lens, 1,

                                    xlat, 1, 1, 0, 0, logctx);

}

/**

 * nodes size must be 2*nb_codes

 * first nb_codes nodes.count must be set

 */

int ff_huff_build_tree(void *logctx, VLC *vlc, int nb_codes, int nb_bits,

                       Node *nodes, HuffCmp cmp, int flags)

{

    int i, j;

    int cur_node;

    int64_t sum = 0;

    for (i = 0; i < nb_codes; i++) {

        nodes[i].sym = i;

        nodes[i].n0 = -2;

        sum += nodes[i].count;

    }

    if (sum >> 31) {

        av_log(logctx, AV_LOG_ERROR,

               "Too high symbol frequencies. "

               "Tree construction is not possible\n");

        return -1;

    }

    AV_QSORT(nodes, nb_codes, Node, cmp);

    cur_node = nb_codes;

    nodes[nb_codes*2-1].count = 0;

    for (i = 0; i < nb_codes * 2 - 1; i += 2) {

        uint32_t cur_count = nodes[i].count + nodes[i+1].count;

        // find correct place to insert new node, and

        // make space for the new node while at it

        for(j = cur_node; j > i + 2; j--){

            if(cur_count > nodes[j-1].count ||

               (cur_count == nodes[j-1].count &&

                !(flags & FF_HUFFMAN_FLAG_HNODE_FIRST)))

                break;

            nodes[j] = nodes[j - 1];

        }

        nodes[j].sym = HNODE;

        nodes[j].count = cur_count;

        nodes[j].n0 = i;

        cur_node++;

    }

    if (build_huff_tree(vlc, nodes, nb_codes * 2 - 2, flags, nb_bits, logctx) < 0) {

        av_log(logctx, AV_LOG_ERROR, "Error building tree\n");

        return -1;

    }

    return 0;

}