text: /*
   * id Quake II CIN Video Decoder
   * Copyright (C) 2003 The FFmpeg project
   *
   * 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
   * id Quake II Cin Video Decoder by Dr. Tim Ferguson
   * For more information about the id CIN format, visit:
   *   http://www.csse.monash.edu.au/~timf/
   *
   * This video decoder outputs PAL8 colorspace data. Interacting with this
   * decoder is a little involved. During initialization, the demuxer must
   * transmit the 65536-byte Huffman table(s) to the decoder via extradata.
   * Then, whenever a palette change is encountered while demuxing the file,
   * the demuxer must use the same extradata space to transmit an
   * AVPaletteControl structure.
   *
   * id CIN video is purely Huffman-coded, intraframe-only codec. It achieves
   * a little more compression by exploiting the fact that adjacent pixels
   * tend to be similar.
   *
   * Note that this decoder could use libavcodec's optimized VLC facilities
   * rather than naive, tree-based Huffman decoding. However, there are 256
   * Huffman tables. Plus, the VLC bit coding order is right -> left instead
   * or left -> right, so all of the bits would have to be reversed. Further,
   * the original Quake II implementation likely used a similar naive
   * decoding algorithm and it worked fine on much lower spec machines.
   */
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  
  #include "avcodec.h"
  #include "decode.h"
  #include "internal.h"
  #include "libavutil/internal.h"
  
  #define HUFFMAN_TABLE_SIZE 64 * 1024
  #define HUF_TOKENS 256
  #define PALETTE_COUNT 256
  
  typedef struct hnode {
    int count;
    unsigned char used;
    int children[2];
  } hnode;
  
  typedef struct IdcinContext {
  
      AVCodecContext *avctx;
  
      const unsigned char *buf;
      int size;
  
      hnode huff_nodes[256][HUF_TOKENS*2];
      int num_huff_nodes[256];
  
      uint32_t pal[256];
  } IdcinContext;
  
  /**
   * Find the lowest probability node in a Huffman table, and mark it as
   * being assigned to a higher probability.
   * @return the node index of the lowest unused node, or -1 if all nodes
   * are used.
   */
  static int huff_smallest_node(hnode *hnodes, int num_hnodes) {
      int i;
      int best, best_node;
  
      best = 99999999;
      best_node = -1;
      for(i = 0; i < num_hnodes; i++) {
          if(hnodes[i].used)
              continue;
          if(!hnodes[i].count)
              continue;
          if(hnodes[i].count < best) {
              best = hnodes[i].count;
              best_node = i;
          }
      }
  
      if(best_node == -1)
          return -1;
      hnodes[best_node].used = 1;
      return best_node;
  }
  
  /*
   * Build the Huffman tree using the generated/loaded probabilities histogram.
   *
   * On completion:
   *  huff_nodes[prev][i < HUF_TOKENS] - are the nodes at the base of the tree.
   *  huff_nodes[prev][i >= HUF_TOKENS] - are used to construct the tree.
   *  num_huff_nodes[prev] - contains the index to the root node of the tree.
   *    That is: huff_nodes[prev][num_huff_nodes[prev]] is the root node.
   */
  static av_cold void huff_build_tree(IdcinContext *s, int prev) {
      hnode *node, *hnodes;
       int num_hnodes, i;
  
      num_hnodes = HUF_TOKENS;
      hnodes = s->huff_nodes[prev];
      for(i = 0; i < HUF_TOKENS * 2; i++)
          hnodes[i].used = 0;
  
      while (1) {
          node = &hnodes[num_hnodes];             /* next free node */
  
          /* pick two lowest counts */
          node->children[0] = huff_smallest_node(hnodes, num_hnodes);
          if(node->children[0] == -1)
              break;      /* reached the root node */
  
          node->children[1] = huff_smallest_node(hnodes, num_hnodes);
          if(node->children[1] == -1)
              break;      /* reached the root node */
  
          /* combine nodes probability for new node */
          node->count = hnodes[node->children[0]].count +
          hnodes[node->children[1]].count;
          num_hnodes++;
      }
  
      s->num_huff_nodes[prev] = num_hnodes - 1;
  }
  
  static av_cold int idcin_decode_init(AVCodecContext *avctx)
  {
      IdcinContext *s = avctx->priv_data;
      int i, j, histogram_index = 0;
      unsigned char *histograms;
  
      s->avctx = avctx;
      avctx->pix_fmt = AV_PIX_FMT_PAL8;
  
      /* make sure the Huffman tables make it */
      if (s->avctx->extradata_size != HUFFMAN_TABLE_SIZE) {
          av_log(s->avctx, AV_LOG_ERROR, "  id CIN video: expected extradata size of %d\n", HUFFMAN_TABLE_SIZE);
          return -1;
      }
  
      /* build the 256 Huffman decode trees */
      histograms = (unsigned char *)s->avctx->extradata;
      for (i = 0; i < 256; i++) {
          for(j = 0; j < HUF_TOKENS; j++)
              s->huff_nodes[i][j].count = histograms[histogram_index++];
          huff_build_tree(s, i);
      }
  
      return 0;
  }
  
  static int idcin_decode_vlcs(IdcinContext *s, AVFrame *frame)
  {
      hnode *hnodes;
      long x, y;
      int prev;
      unsigned char v = 0;
      int bit_pos, node_num, dat_pos;
  
      prev = bit_pos = dat_pos = 0;
      for (y = 0; y < (frame->linesize[0] * s->avctx->height);
          y += frame->linesize[0]) {
          for (x = y; x < y + s->avctx->width; x++) {
              node_num = s->num_huff_nodes[prev];
              hnodes = s->huff_nodes[prev];
  
              while(node_num >= HUF_TOKENS) {
                  if(!bit_pos) {
                      if(dat_pos >= s->size) {
                          av_log(s->avctx, AV_LOG_ERROR, "Huffman decode error.\n");
                          return -1;
                      }
                      bit_pos = 8;
                      v = s->buf[dat_pos++];
                  }
  
                  node_num = hnodes[node_num].children[v & 0x01];
                  v = v >> 1;
                  bit_pos--;
              }
  
              frame->data[0][x] = node_num;
              prev = node_num;
          }
      }
  
      return 0;
  }
  
  static int idcin_decode_frame(AVCodecContext *avctx,
                                void *data, int *got_frame,
                                AVPacket *avpkt)
  {
      const uint8_t *buf = avpkt->data;
      int buf_size = avpkt->size;
      IdcinContext *s = avctx->priv_data;
      AVFrame *frame = data;
      int ret;
  
      s->buf = buf;
      s->size = buf_size;
  
      if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
          return ret;
  
      if (idcin_decode_vlcs(s, frame))
          return AVERROR_INVALIDDATA;
  
      frame->palette_has_changed = ff_copy_palette(s->pal, avpkt, avctx);
      /* make the palette available on the way out */
      memcpy(frame->data[1], s->pal, AVPALETTE_SIZE);
  
      *got_frame = 1;
  
      /* report that the buffer was completely consumed */
      return buf_size;
  }
  
  static const AVCodecDefault idcin_defaults[] = {
      { "max_pixels", "320*240" },
      { NULL },
  };
  
  AVCodec ff_idcin_decoder = {
      .name           = "idcinvideo",
      .long_name      = NULL_IF_CONFIG_SMALL("id Quake II CIN video"),
      .type           = AVMEDIA_TYPE_VIDEO,
      .id             = AV_CODEC_ID_IDCIN,
      .priv_data_size = sizeof(IdcinContext),
      .init           = idcin_decode_init,
      .decode         = idcin_decode_frame,
      .capabilities   = AV_CODEC_CAP_DR1,
      .defaults       = idcin_defaults,
      .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
  };
  