Method ReadCompressedData

IO/XMLParser/vtkXMLDataParser.cxx:704–837

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size_t vtkXMLDataParser::ReadCompressedData(
  unsigned char* data, vtkTypeUInt64 startWord, size_t numWords, size_t wordSize)
{
  // Make sure there are data.
  if (numWords == 0)
  {
    return 0;
  }

  // Find the begin and end offsets into the data.
  vtkTypeUInt64 beginOffset = startWord * wordSize;
  vtkTypeUInt64 endOffset = beginOffset + numWords * wordSize;

  // Find the total size of the data.
  vtkTypeUInt64 totalSize = this->NumberOfBlocks * this->BlockUncompressedSize;
  if (this->PartialLastBlockUncompressedSize)
  {
    totalSize -= this->BlockUncompressedSize;
    totalSize += this->PartialLastBlockUncompressedSize;
  }

  // Make sure there's even data to be read
  if (totalSize == 0)
  {
    return 0;
  }

  // Adjust the size to be a multiple of the wordSize by taking
  // advantage of integer division.  This will only change the value
  // when the input file is invalid.
  totalSize = (totalSize / wordSize) * wordSize;

  // Make sure the begin/end offsets fall within the total size.
  if (beginOffset > totalSize)
  {
    return 0;
  }
  endOffset = std::min(endOffset, totalSize);

  // Find the range of compression blocks to read.
  vtkTypeUInt64 firstBlock = beginOffset / this->BlockUncompressedSize;
  vtkTypeUInt64 lastBlock = endOffset / this->BlockUncompressedSize;

  // Find the offset into the first block where the data begin.
  size_t beginBlockOffset = beginOffset - firstBlock * this->BlockUncompressedSize;

  // Find the offset into the last block where the data end.
  size_t endBlockOffset = endOffset - lastBlock * this->BlockUncompressedSize;

  this->UpdateProgress(0);
  if (firstBlock == lastBlock)
  {
    // Everything fits in one block.
    unsigned char* blockBuffer = this->ReadBlock(firstBlock);
    if (!blockBuffer)
    {
      return 0;
    }