source: thirdparty/blosc/README.rst @ 981e22c

===============================================================
 Blosc: A blocking, shuffling and lossless compression library
===============================================================

:Author: Francesc Alted
:Contact: [email protected]
:URL: http://www.blosc.org
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What is it?
===========

Blosc [1]_ is a high performance compressor optimized for binary data.
It has been designed to transmit data to the processor cache faster
than the traditional, non-compressed, direct memory fetch approach via
a memcpy() OS call.  Blosc is the first compressor (that I'm aware of)
that is meant not only to reduce the size of large datasets on-disk or
in-memory, but also to accelerate memory-bound computations.

It uses the blocking technique (as described in [2]_) to reduce
activity on the memory bus as much as possible. In short, this
technique works by dividing datasets in blocks that are small enough
to fit in caches of modern processors and perform compression /
decompression there.  It also leverages, if available, SIMD
instructions (SSE2, AVX2) and multi-threading capabilities of CPUs, in
order to accelerate the compression / decompression process to a
maximum.

Blosc is actually a metacompressor, that meaning that it can use a range
of compression libraries for performing the actual
compression/decompression. Right now, it comes with integrated support
for BloscLZ (the original one), LZ4, LZ4HC, Snappy, Zlib and Zstd. Blosc
comes with full sources for all compressors, so in case it does not find
the libraries installed in your system, it will compile from the
included sources and they will be integrated into the Blosc library
anyway. That means that you can trust in having all supported
compressors integrated in Blosc in all supported platforms.

You can see some benchmarks about Blosc performance in [3]_

Blosc is distributed using the MIT license, see LICENSES/BLOSC.txt for
details.

.. [1] http://www.blosc.org
.. [2] http://blosc.org/docs/StarvingCPUs-CISE-2010.pdf
.. [3] http://blosc.org/synthetic-benchmarks.html

Meta-compression and other advantages over existing compressors
===============================================================

C-Blosc is not like other compressors: it should rather be called a
meta-compressor.  This is so because it can use different compressors
and filters (programs that generally improve compression ratio).  At
any rate, it can also be called a compressor because it happens that
it already comes with several compressor and filters, so it can
actually work like so.

Currently C-Blosc comes with support of BloscLZ, a compressor heavily
based on FastLZ (http://fastlz.org/), LZ4 and LZ4HC
(https://github.com/Cyan4973/lz4), Snappy
(https://github.com/google/snappy) and Zlib (http://www.zlib.net/), as
well as a highly optimized (it can use SSE2 or AVX2 instructions, if
available) shuffle and bitshuffle filters (for info on how and why
shuffling works, see slide 17 of
http://www.slideshare.net/PyData/blosc-py-data-2014).  However,
different compressors or filters may be added in the future.

C-Blosc is in charge of coordinating the different compressor and
filters so that they can leverage the blocking technique (described
above) as well as multi-threaded execution (if several cores are
available) automatically. That makes that every compressor and filter
will work at very high speeds, even if it was not initially designed
for doing blocking or multi-threading.

Other advantages of Blosc are:

* Meant for binary data: can take advantage of the type size
  meta-information for improved compression ratio (using the
  integrated shuffle and bitshuffle filters).

* Small overhead on non-compressible data: only a maximum of (16 + 4 *
  nthreads) additional bytes over the source buffer length are needed
  to compress *any kind of input*.

* Maximum destination length: contrarily to many other compressors,
  both compression and decompression routines have support for maximum
  size lengths for the destination buffer.

When taken together, all these features set Blosc apart from other
similar solutions.

Compiling your application with a minimalistic Blosc
====================================================

The minimal Blosc consists of the next files (in `blosc/ directory
<https://github.com/Blosc/c-blosc/tree/master/blosc>`_)::

    blosc.h and blosc.c        -- the main routines
    shuffle*.h and shuffle*.c  -- the shuffle code
    blosclz.h and blosclz.c    -- the blosclz compressor

Just add these files to your project in order to use Blosc.  For
information on compression and decompression routines, see `blosc.h
<https://github.com/Blosc/c-blosc/blob/master/blosc/blosc.h>`_.

To compile using GCC (4.9 or higher recommended) on Unix:

.. code-block:: console

   $ gcc -O3 -mavx2 -o myprog myprog.c blosc/*.c -Iblosc -lpthread

Using Windows and MINGW:

.. code-block:: console

   $ gcc -O3 -mavx2 -o myprog myprog.c -Iblosc blosc\*.c

Using Windows and MSVC (2013 or higher recommended):

.. code-block:: console

  $ cl /Ox /Femyprog.exe /Iblosc myprog.c blosc\*.c

In the `examples/ directory
<https://github.com/Blosc/c-blosc/tree/master/examples>`_ you can find
more hints on how to link your app with Blosc.

I have not tried to compile this with compilers other than GCC, clang,
MINGW, Intel ICC or MSVC yet. Please report your experiences with your
own platforms.

Adding support for other compressors with a minimalistic Blosc
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The official cmake files (see below) for Blosc try hard to include
support for LZ4, LZ4HC, Snappy, Zlib inside the Blosc library, so
using them is just a matter of calling the appropriate
`blosc_set_compressor() API call
<https://github.com/Blosc/c-blosc/blob/master/blosc/blosc.h>`_.  See
an `example here
<https://github.com/Blosc/c-blosc/blob/master/examples/many_compressors.c>`_.

Having said this, it is also easy to use a minimalistic Blosc and just
add the symbols HAVE_LZ4 (will include both LZ4 and LZ4HC),
HAVE_SNAPPY and HAVE_ZLIB during compilation as well as the
appropriate libraries. For example, for compiling with minimalistic
Blosc but with added Zlib support do:

.. code-block:: console

   $ gcc -O3 -msse2 -o myprog myprog.c blosc/*.c -Iblosc -lpthread -DHAVE_ZLIB -lz

In the `bench/ directory
<https://github.com/Blosc/c-blosc/tree/master/bench>`_ there a couple
of Makefile files (one for UNIX and the other for MinGW) with more
complete building examples, like switching between libraries or
internal sources for the compressors.

Supported platforms
~~~~~~~~~~~~~~~~~~~

Blosc is meant to support all platforms where a C89 compliant C
compiler can be found.  The ones that are mostly tested are Intel
(Linux, Mac OSX and Windows) and ARM (Linux), but exotic ones as IBM
Blue Gene Q embedded "A2" processor are reported to work too.

Compiling the Blosc library with CMake
======================================

Blosc can also be built, tested and installed using CMake_. Although
this procedure might seem a bit more involved than the one described
above, it is the most general because it allows to integrate other
compressors than BloscLZ either from libraries or from internal
sources. Hence, serious library developers are encouraged to use this
way.

The following procedure describes the "out of source" build.

Create the build directory and move into it:

.. code-block:: console

  $ mkdir build
  $ cd build

Now run CMake configuration and optionally specify the installation
directory (e.g. '/usr' or '/usr/local'):

.. code-block:: console

  $ cmake -DCMAKE_INSTALL_PREFIX=your_install_prefix_directory ..

CMake allows to configure Blosc in many different ways, like prefering
internal or external sources for compressors or enabling/disabling
them.  Please note that configuration can also be performed using UI
tools provided by CMake_ (ccmake or cmake-gui):

.. code-block:: console

  $ ccmake ..      # run a curses-based interface
  $ cmake-gui ..   # run a graphical interface

Build, test and install Blosc:

.. code-block:: console

  $ cmake --build .
  $ ctest
  $ cmake --build . --target install

The static and dynamic version of the Blosc library, together with
header files, will be installed into the specified
CMAKE_INSTALL_PREFIX.

.. _CMake: http://www.cmake.org

Once you have compiled your Blosc library, you can easily link your
apps with it as shown in the `example/ directory
<https://github.com/Blosc/c-blosc/blob/master/examples>`_.

Adding support for other compressors (LZ4, LZ4HC, Snappy, Zlib) with CMake
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The CMake files in Blosc are configured to automatically detect other
compressors like LZ4, LZ4HC, Snappy or Zlib by default.  So as long as
the libraries and the header files for these libraries are accessible,
these will be used by default.  See an `example here
<https://github.com/Blosc/c-blosc/blob/master/examples/many_compressors.c>`_.

*Note on Zlib*: the library should be easily found on UNIX systems,
although on Windows, you can help CMake to find it by setting the
environment variable 'ZLIB_ROOT' to where zlib 'include' and 'lib'
directories are. Also, make sure that Zlib DDL library is in your
'\Windows' directory.

However, the full sources for LZ4, LZ4HC, Snappy and Zlib have been
included in Blosc too. So, in general, you should not worry about not
having (or CMake not finding) the libraries in your system because in
this case, their sources will be automatically compiled for you. That
effectively means that you can be confident in having a complete
support for all the supported compression libraries in all supported
platforms.

If you want to force Blosc to use external libraries instead of
the included compression sources:

.. code-block:: console

  $ cmake -DPREFER_EXTERNAL_LZ4=ON ..

You can also disable support for some compression libraries:

.. code-block:: console

  $ cmake -DDEACTIVATE_SNAPPY=ON ..

Mac OSX troubleshooting
~~~~~~~~~~~~~~~~~~~~~~~

If you run into compilation troubles when using Mac OSX, please make
sure that you have installed the command line developer tools.  You
can always install them with:

.. code-block:: console

  $ xcode-select --install

Wrapper for Python
==================

Blosc has an official wrapper for Python.  See:

https://github.com/Blosc/python-blosc

Command line interface and serialization format for Blosc
=========================================================

Blosc can be used from command line by using Bloscpack.  See:

https://github.com/Blosc/bloscpack

Filter for HDF5
===============

For those who want to use Blosc as a filter in the HDF5 library,
there is a sample implementation in the blosc/hdf5 project in:

https://github.com/Blosc/hdf5

Mailing list
============

There is an official mailing list for Blosc at:

[email protected]
http://groups.google.es/group/blosc

Acknowledgments
===============

See THANKS.rst.


----

  **Enjoy data!**