Github user xndai commented on a diff in the pull request:

    https://github.com/apache/orc/pull/301#discussion_r215486619
  
    --- Diff: c++/src/Compression.cc ---
    @@ -899,6 +907,166 @@ DIAGNOSTIC_POP
         return static_cast<uint64_t>(result);
       }
     
    +  /**
    +   * Block compression base class
    +   */
    +  class BlockCompressionStream: public CompressionStreamBase {
    +  public:
    +    BlockCompressionStream(OutputStream * outStream,
    +                           int compressionLevel,
    +                           uint64_t capacity,
    +                           uint64_t blockSize,
    +                           MemoryPool& pool)
    +                           : CompressionStreamBase(outStream,
    +                                                   compressionLevel,
    +                                                   capacity,
    +                                                   blockSize,
    +                                                   pool)
    +                           , compressorBuffer(pool) {
    +      // PASS
    +    }
    +
    +    virtual bool Next(void** data, int*size) override;
    +    virtual std::string getName() const override = 0;
    +
    +  protected:
    +    // compresses a block and returns the compressed size
    +    virtual uint64_t doBlockCompression() = 0;
    +
    +    // return maximum possible compression size for allocating space for
    +    // compressorBuffer below
    +    virtual uint64_t estimateMaxCompressionSize() = 0;
    +
    +    // should allocate max possible compressed size
    +    DataBuffer<unsigned char> compressorBuffer;
    +  };
    +
    +  bool BlockCompressionStream::Next(void** data, int*size) {
    +    if (bufferSize != 0) {
    +      ensureHeader();
    +
    +      // perform compression
    +      size_t totalCompressedSize = doBlockCompression();
    +
    +      const unsigned char * dataToWrite = nullptr;
    +      int totalSizeToWrite = 0;
    +      char * header = outputBuffer + outputPosition - 3;
    +
    +      if (totalCompressedSize >= static_cast<size_t>(bufferSize)) {
    +        writeHeader(header, static_cast<size_t>(bufferSize), true);
    +        dataToWrite = rawInputBuffer.data();
    +        totalSizeToWrite = bufferSize;
    +      } else {
    +        writeHeader(header, totalCompressedSize, false);
    +        dataToWrite = compressorBuffer.data();
    +        totalSizeToWrite = static_cast<int>(totalCompressedSize);
    +      }
    +
    +      char * dst = header + 3;
    +      while (totalSizeToWrite > 0) {
    +        if (outputPosition >= outputSize) {
    --- End diff --
    
    assert outputPosition not larger than outputSize.


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