ZLIB in ROOT

meyerma · June 28, 2023, 4:12am

Hello,

I have to read some text files using zlib decompression. I have noticed that ROOT is implementing a Compression class. It seems to be very related to ROOT files decompression.

Is there a way to take advantage of this already existing dependencies in root ?

ferhue · June 28, 2023, 3:58pm

what about: GitHub - mateidavid/zstr: A C++ header-only ZLib wrapper

meyerma · June 29, 2023, 1:34am

Hi @ferhue,

Thank you ! Yes I have implemented it, but I wanted to be sure this was not already done in ROOT directly without handling additional deps in my C++ compilation

Is that so ?

ferhue · June 29, 2023, 8:08am

Maybe @linev or @pcanal know if there is something of the sort directly withiin ROOT.

linev · June 29, 2023, 8:28am

Hi,

ROOT internally uses several compression algorithms.
But there is no documentation or tutorials for that.

There are only low-level functions which can be in RZip.h include file:

github.com

root-project/root/blob/master/core/zip/inc/RZip.h

// @(#)root/zip:$Id$
// Author: Sergey Linev   7 July 2014

/*************************************************************************
 * Copyright (C) 1995-2014, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/
#include "Compression.h"

/**
 * These are definitions of various free functions for the C-style compression routines in ROOT.
 */

#ifndef ROOT_RZip
#define ROOT_RZip

extern "C" unsigned long R__crc32(unsigned long crc, const unsigned char* buf, unsigned int len);

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One usually compress data using R__zipMultipleAlgorithm function and decompress with R__unzip.
You could try to find examples in ROOT source code. Like in TMessage class:

github.com

root-project/root/blob/master/net/net/src/TMessage.cxx

// @(#)root/net:$Id$
// Author: Fons Rademakers   19/12/96

/*************************************************************************
 * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

//////////////////////////////////////////////////////////////////////////
//                                                                      //
// TMessage                                                             //
//                                                                      //
// Message buffer class used for serializing objects and sending them   //
// over a network. This class inherits from TBuffer the basic I/O       //
// serializer.                                                          //
//                                                                      //
//////////////////////////////////////////////////////////////////////////

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Be aware of kMAXZIPBUF constant which defines maximal buffer size for compression.

Regards,
Sergey

system · July 13, 2023, 8:29am

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