This is an HDF5 Plugin for the SPERR compressor.
It is registered with the HDF Group with a plugin ID of 32028.
Needless to say, H5Z-SPERR depends on both HDF5 and SPERR.
After HDF5 and SPERR are installed, H5Z-SPERR can be configured and built using cmake:
export HDF5_ROOT=/path/to/your/preferred/HDF5/installation
mkdir build-H5-SPERR && cd build-H5-SPERR
cmake -DSPERR_INSTALL_DIR=/path/to/SPERR/installation \
-DCMAKE_INSTALL_PREFIX=/path/to/install/this/plugin \
/path/to/H5Z-SPERR/source/code
make installThe plugin library file libh5z-sperr.so will be placed at directory /path/to/install/this/plugin.
Using the dynamically loaded plugin mechanism by HDF5,
one may use H5Z-SPERR by simply setting the environment variable HDF5_PLUGIN_PATH to the directory containing the plugin
library file:
export HDF5_PLUGIN_PATH=/path/to/install/this/pluginThe user program does not need to link to this plugin or SPERR; it only needs to specify the plugin ID of 32028.
To apply SPERR compression using the HDF5 plugin, one needs to specify 1) what compression mode and 2) what compression quality to use. Supported compression modes and qualities are summarized below:
| Mode No. | Mode Meaning | Meaningful Quality Range |
|---|---|---|
| 1 | Fixed bit-per-pixel (BPP) | 0.0 < quality < 64.0 |
| 2 | Fixed peak signal-to-noise ratio (PSNR) | 0.0 < quality |
| 3 | Fixed point-wise error (PWE) | 0.0 < quality |
In addition, the rank order needs to be swapped sometimes to achieve the best compression.
For example, if a 2D slice of dimensions (64, 128) has the dim=128 rank being the fastest
varying rank, then this slice needs a "rank order swap" to achieve the best compression.
In general, given dimensions of (NX, NY, NZ), we want the X rank to be varying the fastest,
and the Z rank to be varying the slowest, before the data is passed to the compressor.
"Rank order swap" helps to achieve it.
The HDF5 libraries takes in these compression parameters as one or more 32-bit unsigned int values,
which are named cd_values[] in most HDF5 routines.
In the case of H5Z-SPERR, there is exactly one unsigned int used to carry this information.
Using the HDF5 programming interface, cd_values[] carrying the compression parameters are passed
to HDF5 routines such as H5Pset_filter(). To find the correct cd_values[], a user
needs to include the header h5z-sperr.h
from this repository
and call the unsigned int H5Z_SPERR_make_cd_values(int mode, double quality, int swap) function
to have these two pieces of information correctly encoded. For example:
int mode = 3; /* Fixed PWE compression */
double quality = 1e-6; /* PWE tolerance = 1e-6 */
int swap = 1; /* Enable rank order swap */
unsigned int cd_values = H5Z_SPERR_make_cd_values(mode, quality, swap); /* Generate cd_values */
H5Pset_filter(prop, 32028, H5Z_FLAG_MANDATORY, 1, &cd_values); /* Specify SPERR compression in HDF5 */See a complete example here.
After building H5Z-SPERR, a command line tool named generate_cd_values becomes available to encode 1) SPERR
compression mode, 2) quality, and 3) if to perform rank order swap
into a single unsigned int. The produced value can then be used in other command line tools such as h5repack.
In the following example, generate_cd_values reports that 268651725u encodes fixed-rate compression with
a bitrate of 3.3 bit-per-value, without doing rank order swap.
$ ./bin/generate_cd_values 1 3.3
For fixed-rate compression with a bitrate of 3.3, without swapping rank orders,
H5Z-SPERR cd_values = 268651725u (Filter ID = 32028).
Please use this value as a single 32-bit unsigned integer in your applications.Note: an integer produced by generate_cd_values can be decoded by another command line tool, decode_cd_values,
to show the coded compression parameters.
H5Z-SPERR also facilitates the application of SPERR compression on
NetCDF-4 files;
one simply needs to define the filter on a variable:
nc_def_var_filter(ncid, varid, 32028, 1, &cd_values);See a complete example here.