Function decompress

src/IECore/StreamIndexedIO.cpp:491–529

decompress a memory buffer which is formed by a number of blosc compressed blocks returns the number of compression blocks 'outputBuffer' contains the decompressed data and is resized in this function if not large enough.

/// returns the number of compression blocks
/// 'outputBuffer' contains the decompressed data and is resized in this function if not large enough.
size_t decompress( const char *data, size_t size, std::vector<char> &outputBuffer, int threadCount )
{
	std::vector<std::pair<size_t, size_t>> blockSizes;
	size_t totalDecompressedSize = 0;
	size_t compressedBytesRead = 0;

	while( compressedBytesRead < size )
	{
		size_t compressedNumBytes = 0, decompressedNumBytes = 0, blockSize = 0;
		blosc_cbuffer_sizes( &data[compressedBytesRead], &decompressedNumBytes, &compressedNumBytes, &blockSize );

		blockSizes.push_back( std::make_pair( compressedNumBytes, decompressedNumBytes ) );
		totalDecompressedSize += decompressedNumBytes;
		compressedBytesRead += compressedNumBytes;
	}

	if( outputBuffer.size() < totalDecompressedSize )
	{
		std::vector<char> b ( totalDecompressedSize );
		outputBuffer.swap( b );
	}

	compressedBytesRead = 0;
	size_t decompressedBytesWritten = 0;
	for( const auto &blockSize : blockSizes )
	{
		int bloscResult = blosc_decompress_ctx( &data[compressedBytesRead], &outputBuffer[decompressedBytesWritten], blockSize.second, threadCount );

		if( bloscResult <= 0 )
		{
			throw IECore::IOException( "StreamIndexedIO (decompress) - Corrupted compressed archive" );
		}

		compressedBytesRead += blockSize.first;
		decompressedBytesWritten += blockSize.second;
	}

	return blockSizes.size();
}

} // namespace