Contribute

This project follows the standard open-source project github workflow, which is described in other projects like matplotlib or scikit-image.

Testing

To run self-contained tests, from Python:

import hdf5plugin.test
hdf5plugin.test.run_tests()

Or, from the command line:

python -m hdf5plugin.test

To also run tests relying on actual HDF5 files, run from the source directory:

python test/test.py

This tests the installed version of hdf5plugin.

Building documentation

Documentation relies on Sphinx.

To build documentation, run from the project root directory:

python setup.py build
PYTHONPATH=build/lib.<os>-<machine>-<pyver>/ sphinx-build -b html doc/ build/html

Guidelines to add a compression filter

This briefly describes the steps to add a HDF5 compression filter to the zoo.

Add the source of the HDF5 filter and compression algorithm code in a subdirectory in src/[filter]. Best is to use git subtree else copy the files there (including the license file). A released version of the filter + compression library should be used.

git subtree command:
```
git subtree add --prefix=src/[filter]  [git repository]  [release tag] --squash
```
Update setup.py to build the filter dynamic library by adding an extension using the HDF5PluginExtension class (a subclass of setuptools.Extension) which adds extra files and compile options to enable dynamic loading of the filter. The name of the extension should be hdf5plugin.plugins.libh5<filter_name>.
In case of import errors related to HDF5-related undefined symbols, add eventual missing functions under src/hdf5_dl.c.
Add a “CONSTANT” in src/hdf5plugin/_filters.py named with the FILTER_NAME_ID which value is the HDF5 filter ID (See HDF5 registered filters).
Add a compression options helper class named FilterName in hdf5plugins/_filters.py which should inherit from _FilterRefClass. This is intended to ease the usage of h5py.Group.create_dataset compression_opts argument. It must have a filter_name class attribute with the same name as in the extension defined in setup.py (without the libh5 prefix) . This name is used to find the filter library.
Add FilterName to hdf5plugin._filters.FILTER_CLASSES.
Add to hdf5plugin/__init__.py the import of the filter ID and helper class: from ._filters import FILTER_NAME_ID, FilterName # noqa
Add tests:
- In test/test.py for testing reading a compressed file that was produced with another software.
- In src/hdf5plugin/test.py for tests that writes data using the compression filter and the compression options helper function and reads back the data.
Update the doc/information.rst file to document:
- The version of the HDF5 filter that is embedded in hdf5plugin.
- The license of the filter (by adding a link to the license file).
Update the doc/usage.rst file to document:
- The hdf5plugin.<FilterName> compression argument helper class.
Update doc/contribute.rst to document the format of compression_opts expected by the filter (see h5py custom compression filters).

Low-level compression filter arguments

Compression filters can be configured with the compression_opts argument of h5py.Group.create_dataset method by providing a tuple of integers.

The meaning of those integers is filter dependent and is described below.

bitshuffle

compression_opts: (block_size, compression, level)

block size: Number of elements (not bytes) per block. It MUST be a mulitple of 8. Default: 0 for a block size of about 8 kB.
compression:
- 0: No compression
- 2: LZ4
- 3: Zstd
level: Compression level, only used with Zstd compression.

By default the filter uses bitshuffle, but does NOT compress with LZ4.

blosc

compression_opts: (0, 0, 0, 0, compression level, shuffle, compression)

First 4 values are reserved.
compression level: From 0 (no compression) to 9 (maximum compression). Default: 5.
shuffle: Shuffle filter:
- 0: no shuffle
- 1: byte shuffle
- 2: bit shuffle
compression: The compressor blosc ID:
- 0: blosclz (default)
- 1: lz4
- 2: lz4hc
- 3: snappy
- 4: zlib
- 5: zstd

By default the filter uses byte shuffle and blosclz.

bzip2

compression_opts: (block size,)

block_size: Size of the blocks as a multiple of 100k. It must be in the range [1, 9].

lz4

compression_opts: (block_size,)

block size: Number of bytes per block. Default 0 for a block size of 1GB. It MUST be < 1.9 GB.

sz

compression_opts:

error_bound_mode (int32)
abs_error high (big endian float64)
abs_error low
rel_error high (big endian float64)
rel_error low
pw_rel_error high (big endian float64)
pw_rel_error low
psnr high (big endian float64)
psnr low

The set_local function prepends:

For dim size from 2 to 5:

(dim size, data type, r1, r2, r3 (if dim size >= 3), r4 (if dim size >= 4), r5 (if dim size == 5))

rX are set up to dim size (e.g., For dim size == 2 only r1 and r2 are used)
For dim size == 1: r1 is stored on 64 bits:

(dim size, data type, r1 most-significant bytes, r1 least-significant bytes)

zfp

For more information, see zfp modes and hdf5-zfp generic interface.

The first value of compression_opts is mode. The following values depends on the value of mode:

Fixed-rate mode: (1, 0, rateHigh, rateLow, 0, 0) Rate, i.e., number of compressed bits per value, as a double stored as:
- rateHigh: High 32-bit word of the rate double.
- rateLow: Low 32-bit word of the rate double.
Fixed-precision mode: (2, 0, prec, 0, 0, 0)
- prec: Number of uncompressed bits per value.
Fixed-accuracy mode: (3, 0, accHigh, accLow, 0, 0) Accuracy, i.e., absolute error tolerance, as a double stored as:
- accHigh: High 32-bit word of the accuracy double.
- accLow: Low 32-bit word of the accuracy double.
Expert mode: (4, 0, minbits, maxbits, maxprec, minexp)
- minbits: Minimum number of compressed bits used to represent a block.
- maxbits: Maximum number of bits used to represent a block.
- maxprec: Maximum number of bit planes encoded.
- minexp: Smallest absolute bit plane number encoded.
Reversible mode: (5, 0, 0, 0, 0, 0)

zstd

compression_opts: (clevel,)

clevel: Compression level from 1 (lowest compression) to 22 (maximum compression). Ultra compression extends from 20 through 22. Default: 3.