Function compress

src/IECore/StreamIndexedIO.cpp:411–486

compress 'size' bytes at 'data' into 'outputBuffer' compressionLevel, compressor & threadCount are passed directly to blosc ( see blosc.h ) if 'size' is greater than the max buffer blosc can handle we split into a number of independently compressed blocks. returns the number of compression blocks 'outputBuffer' contains the compressed block data and is resized in this function. 'maxBlockSize' is

/// 'outputBuffer' contains the compressed block data and is resized in this function.
/// 'maxBlockSize' is useful for testing the compression block size without using buffers greater than 2GB
size_t compress(
	const char *data,
	size_t size,
	std::vector<char> &outputBuffer,
	int compressionLevel,
	const std::string &compressor,
	int threadCount,
	std::optional<size_t> maxBlockSize = std::optional<size_t>(),
	size_t minCompressedBlockSize = 1024U
)
{
	const size_t maxCompressedBlockSize = maxBlockSize.value_or( BLOSC_MAX_BUFFERSIZE );

	if( size < minCompressedBlockSize )
	{
		return 0;
	}

	size_t bytesToCompress = size;
	const char *currentBlockCompressed = data;

	size_t numBlocks = 0;

	/// this isn't enough space in some edge cases but is sufficient in the common case
	/// and we check if we have enough size in the compression loop
	outputBuffer.resize( size + BLOSC_MAX_OVERHEAD );
	char *writePtr = outputBuffer.data();
	size_t writerBufferBytes = outputBuffer.size();

	size_t totalCompressedSize = 0;

	while ( bytesToCompress )
	{
		size_t currentBlockUncompressedSize = std::min( maxCompressedBlockSize, bytesToCompress );
		size_t compressedBufferMaxSize = currentBlockUncompressedSize + BLOSC_MAX_OVERHEAD;
		if( writerBufferBytes < compressedBufferMaxSize )
		{
			size_t additionalBytes = (size_t) ( compressedBufferMaxSize - writerBufferBytes );
			outputBuffer.resize( outputBuffer.size() + additionalBytes );
		}

		int compressedSize = blosc_compress_ctx(
			compressionLevel,
			true,
			4,
			currentBlockUncompressedSize,
			currentBlockCompressed,
			writePtr,
			compressedBufferMaxSize,
			compressor.c_str(),
			0,
			threadCount
		);

		if ( compressedSize < 0 )
		{
			outputBuffer.clear();
			return 0;