Function getTreeInflateDynamic

deps/lodepng/lodepng.cpp:991–1136

get the tree of a deflated block with dynamic tree, the tree itself is also Huffman compressed with a known tree*/

/*get the tree of a deflated block with dynamic tree, the tree itself is also Huffman compressed with a known tree*/
static unsigned getTreeInflateDynamic(HuffmanTree* tree_ll, HuffmanTree* tree_d,
                                      const unsigned char* in, size_t* bp, size_t inlength)
{
  /*make sure that length values that aren't filled in will be 0, or a wrong tree will be generated*/
  unsigned error = 0;
  unsigned n, HLIT, HDIST, HCLEN, i;
  size_t inbitlength = inlength * 8;

  /*see comments in deflateDynamic for explanation of the context and these variables, it is analogous*/
  unsigned* bitlen_ll = 0; /*lit,len code lengths*/
  unsigned* bitlen_d = 0; /*dist code lengths*/
  /*code length code lengths ("clcl"), the bit lengths of the huffman tree used to compress bitlen_ll and bitlen_d*/
  unsigned* bitlen_cl = 0;
  HuffmanTree tree_cl; /*the code tree for code length codes (the huffman tree for compressed huffman trees)*/

  if((*bp) + 14 > (inlength << 3)) return 49; /*error: the bit pointer is or will go past the memory*/

  /*number of literal/length codes + 257. Unlike the spec, the value 257 is added to it here already*/
  HLIT =  readBitsFromStream(bp, in, 5) + 257;
  /*number of distance codes. Unlike the spec, the value 1 is added to it here already*/
  HDIST = readBitsFromStream(bp, in, 5) + 1;
  /*number of code length codes. Unlike the spec, the value 4 is added to it here already*/
  HCLEN = readBitsFromStream(bp, in, 4) + 4;

  if((*bp) + HCLEN * 3 > (inlength << 3)) return 50; /*error: the bit pointer is or will go past the memory*/

  HuffmanTree_init(&tree_cl);

  while(!error)
  {
    /*read the code length codes out of 3 * (amount of code length codes) bits*/

    bitlen_cl = (unsigned*)lodepng_malloc(NUM_CODE_LENGTH_CODES * sizeof(unsigned));
    if(!bitlen_cl) ERROR_BREAK(83 /*alloc fail*/);

    for(i = 0; i != NUM_CODE_LENGTH_CODES; ++i)
    {
      if(i < HCLEN) bitlen_cl[CLCL_ORDER[i]] = readBitsFromStream(bp, in, 3);
      else bitlen_cl[CLCL_ORDER[i]] = 0; /*if not, it must stay 0*/
    }

    error = HuffmanTree_makeFromLengths(&tree_cl, bitlen_cl, NUM_CODE_LENGTH_CODES, 7);
    if(error) break;

    /*now we can use this tree to read the lengths for the tree that this function will return*/
    bitlen_ll = (unsigned*)lodepng_malloc(NUM_DEFLATE_CODE_SYMBOLS * sizeof(unsigned));
    bitlen_d = (unsigned*)lodepng_malloc(NUM_DISTANCE_SYMBOLS * sizeof(unsigned));
    if(!bitlen_ll || !bitlen_d) ERROR_BREAK(83 /*alloc fail*/);
    for(i = 0; i != NUM_DEFLATE_CODE_SYMBOLS; ++i) bitlen_ll[i] = 0;
    for(i = 0; i != NUM_DISTANCE_SYMBOLS; ++i) bitlen_d[i] = 0;

    /*i is the current symbol we're reading in the part that contains the code lengths of lit/len and dist codes*/
    i = 0;
    while(i < HLIT + HDIST)
    {
      unsigned code = huffmanDecodeSymbol(in, bp, &tree_cl, inbitlength);
      if(code <= 15) /*a length code*/
      {