/*

  * 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 "avcodec.h"

 #include "get_bits.h"

 #include "huffman.h"
 
 /* symbol for Huffman tree node */
 #define HNODE -1
 

 typedef struct {
     uint64_t val;
     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;
     }
 }
 
 void ff_huff_gen_len_table(uint8_t *dst, const uint64_t *stats)
 {
     HeapElem h[256];
     int up[2*256];
     int len[2*256];
     int offset, i, next;
     int size = 256;
 
     for (offset = 1; ; offset <<= 1) {
         for (i=0; i < size; i++) {
             h[i].name = i;
             h[i].val = (stats[i] << 8) + 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[i] = len[up[i]] + 1;
             if (dst[i] >= 32) break;
         }
         if (i==size) break;
     }
 }

 static void get_tree_codes(uint32_t *bits, int16_t *lens, uint8_t *xlat,
                            Node *nodes, int node,
                            uint32_t pfx, int pl, int *pos, int no_zero_count)

 {
     int s;
 
     s = nodes[node].sym;

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

         bits[*pos] = pfx;
         lens[*pos] = pl;
         xlat[*pos] = s;
         (*pos)++;

     } else {

         pfx <<= 1;
         pl++;

         get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0, pfx, pl,
                        pos, no_zero_count);

         pfx |= 1;

         get_tree_codes(bits, lens, xlat, nodes, nodes[node].n0 + 1, pfx, pl,
                        pos, no_zero_count);

     }
 }
 

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

 {

     int no_zero_count = !(flags & FF_HUFFMAN_FLAG_ZERO_COUNT);

     uint32_t bits[256];
     int16_t lens[256];
     uint8_t xlat[256];
     int pos = 0;
 

     get_tree_codes(bits, lens, xlat, nodes, head, 0, 0,
                    &pos, no_zero_count);

     return ff_init_vlc_sparse(vlc, nb_bits, pos, lens, 2, 2, bits, 4, 4, xlat, 1, 1, 0);

 }
 
 
 /**

  * nodes size must be 2*nb_codes

  * first nb_codes nodes.count must be set
  */

 int ff_huff_build_tree(AVCodecContext *avctx, 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(avctx, AV_LOG_ERROR,
                "Too high symbol frequencies. "
                "Tree construction is not possible\n");

         return -1;
     }
     qsort(nodes, nb_codes, sizeof(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) < 0) {

         av_log(avctx, AV_LOG_ERROR, "Error building tree\n");
         return -1;
     }
     return 0;
 }