h5ex_d_nbit.c

/************************************************************

  This example shows how to read and write data to a dataset
  using the N-Bit filter.  The program first checks if the
  N-Bit filter is available, then if it is it writes
  integers to a dataset using N-Bit, then closes the file.
  Next, it reopens the file, reads back the data, and
  outputs the type of filter and the maximum value in the
  dataset to the screen.

 ************************************************************/

#include "hdf5.h"
#include <stdio.h>
#include <stdlib.h>

#define FILE    "h5ex_d_nbit.h5"
#define DATASET "DS1"
#define DIM0    32
#define DIM1    64
#define CHUNK0  4
#define CHUNK1  8

int
main(void)
{
    hid_t file  = H5I_INVALID_HID;
    hid_t space = H5I_INVALID_HID;
    hid_t dset  = H5I_INVALID_HID;
    hid_t dtype = H5I_INVALID_HID;
    hid_t dcpl  = H5I_INVALID_HID;
    /* Handles */
    herr_t       status;
    htri_t       avail;
    H5Z_filter_t filter_type;
    hsize_t      dims[2]  = {DIM0, DIM1};
    hsize_t      chunk[2] = {CHUNK0, CHUNK1};
    size_t       nelmts;
    unsigned int flags;
    unsigned int filter_info;
    int          wdata[DIM0][DIM1]; /* Write buffer */
    int          rdata[DIM0][DIM1]; /* Read buffer */
    int          max;
    hsize_t      i, j;

    /*
     * Check if N-Bit compression is available and can be used for both
     * compression and decompression.  Normally we do not perform error
     * checking in these examples for the sake of clarity, but in this
     * case we will make an exception because this filter is an
     * optional part of the hdf5 library.
     */
    avail = H5Zfilter_avail(H5Z_FILTER_NBIT);
    if (!avail) {
        printf("N-Bit filter not available.\n");
        return 1;
    }
    status = H5Zget_filter_info(H5Z_FILTER_NBIT, &filter_info);
    if (!(filter_info & H5Z_FILTER_CONFIG_ENCODE_ENABLED) ||
        !(filter_info & H5Z_FILTER_CONFIG_DECODE_ENABLED)) {
        printf("N-Bit filter not available for encoding and decoding.\n");
        return 1;
    }

    /*
     * Initialize data.
     */
    for (i = 0; i < DIM0; i++)
        for (j = 0; j < DIM1; j++)
            wdata[i][j] = i * j - j;

    /*
     * Create a new file using the default properties.
     */
    file = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    /*
     * Create dataspace.  Setting maximum size to NULL sets the maximum
     * size to be the current size.
     */
    space = H5Screate_simple(2, dims, NULL);

    /*
     * Create the datatype to use with the N-Bit filter.  It has an
     * uncompressed size of 32 bits, but will have a size of 16 bits
     * after being packed by the N-Bit filter.
     */
    dtype  = H5Tcopy(H5T_STD_I32LE);
    status = H5Tset_precision(dtype, 16);
    status = H5Tset_offset(dtype, 5);

    /*
     * Create the dataset creation property list, add the N-Bit filter
     * and set the chunk size.
     */
    dcpl   = H5Pcreate(H5P_DATASET_CREATE);
    status = H5Pset_nbit(dcpl);
    status = H5Pset_chunk(dcpl, 2, chunk);

    /*
     * Create the dataset.
     */
    dset = H5Dcreate(file, DATASET, dtype, space, H5P_DEFAULT, dcpl, H5P_DEFAULT);

    /*
     * Write the data to the dataset.
     */
    status = H5Dwrite(dset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, wdata[0]);

    /*
     * Close and release resources.
     */
    status = H5Pclose(dcpl);
    status = H5Tclose(dtype);
    status = H5Dclose(dset);
    status = H5Sclose(space);
    status = H5Fclose(file);

    /*
     * Now we begin the read section of this example.
     */

    /*
     * Open file and dataset using the default properties.
     */
    file = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT);
    dset = H5Dopen(file, DATASET, H5P_DEFAULT);

    /*
     * Retrieve dataset creation property list.
     */
    dcpl = H5Dget_create_plist(dset);

    /*
     * Retrieve and print the filter type.  Here we only retrieve the
     * first filter because we know that we only added one filter.
     */
    nelmts      = 0;
    filter_type = H5Pget_filter(dcpl, 0, &flags, &nelmts, NULL, 0, NULL, &filter_info);
    printf("Filter type is: ");
    switch (filter_type) {
        case H5Z_FILTER_DEFLATE:
            printf("H5Z_FILTER_DEFLATE\n");
            break;
        case H5Z_FILTER_SHUFFLE:
            printf("H5Z_FILTER_SHUFFLE\n");
            break;
        case H5Z_FILTER_FLETCHER32:
            printf("H5Z_FILTER_FLETCHER32\n");
            break;
        case H5Z_FILTER_SZIP:
            printf("H5Z_FILTER_SZIP\n");
            break;
        case H5Z_FILTER_NBIT:
            printf("H5Z_FILTER_NBIT\n");
            break;
        case H5Z_FILTER_SCALEOFFSET:
            printf("H5Z_FILTER_SCALEOFFSET\n");
    }

    /*
     * Read the data using the default properties.
     */
    status = H5Dread(dset, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, rdata[0]);

    /*
     * Find the maximum value in the dataset, to verify that it was
     * read correctly.
     */
    max = rdata[0][0];
    for (i = 0; i < DIM0; i++)
        for (j = 0; j < DIM1; j++)
            if (max < rdata[i][j])
                max = rdata[i][j];

    /*
     * Print the maximum value.
     */
    printf("Maximum value in %s is: %d\n", DATASET, max);

    /*
     * Close and release resources.
     */
    status = H5Pclose(dcpl);
    status = H5Dclose(dset);
    status = H5Fclose(file);

    return 0;
}