How to get the size of compressed data?

[lenalana]

Please I need to print all the decompress data how can I get on the size of decompress data?

int8_t *data2 = (int8_t*) SZ_decompress(SZ_INT8, bytes, byteLength, r5, r4, r3, r2, r1);
    for(int i=0;i<?;i++) {
      printf("SZ_decompress data  %d   \n"data2[i]); 
    }

[robertu94]

When you call SZ_Compress, the routine populates memory pointed to by the outSize input parameter that you pass to SZ_decompress here as byteLength. You will need to store/communicate r1-r5 separately on your own. LibPressio has the ability to store this information in the compressed byte stream when using SZ for you if you need this. Here is what that would look like in C:

#include <libpressio.h>
#include <stddef.h>
#include <stdlib.h>
#include <limits.h>
#include <stdio.h>

int main() {
    //get a dataset from somewhere, here we make it randomly
    size_t r1 = 500, r2=500, r3=100;
    int8_t* ptr = (int8_t*) malloc(sizeof(int8_t) * r1*r2*r3);
    for (size_t i = 0; i < r1; ++i) {
        for (int j = 0; j < r2; ++j) {
            for (int k = 0; k < r3; ++k) {
                ptr[i*r3*r2+j*r3+k] = rand() % CHAR_MAX;
            }
        }
    }

    // configure compressor; here we use manifest to store metadata about compression, and SZ2 to actually compress it with an absolute error bound of 1e-4
    struct pressio* library = pressio_instance();
    struct pressio_compressor* compressor = pressio_get_compressor(library, "manifest");
    struct pressio_options* opts = pressio_options_new();
    pressio_options_set_double(opts, "pressio:abs", 1e-4);
    pressio_options_set_string(opts, "manifest:compressor", "sz");
    pressio_compressor_set_options(compressor, opts);
    pressio_options_free(opts);

    //compress
    size_t dims[] ={r1,r2,r3};
    struct pressio_data* input = pressio_data_new_nonowning(pressio_int8_dtype, ptr, sizeof(dims)/sizeof(dims[0]), dims);
    struct pressio_data* compressed = pressio_data_new_empty(pressio_byte_dtype, 0, NULL);
    struct pressio_data* decompressed = pressio_data_new_empty(pressio_byte_dtype, 0, NULL);
    if(pressio_compressor_compress(compressor, input, compressed)) {
        printf("compression error: %s\n", pressio_compressor_error_msg(compressor));
        exit(1);
    }

    //decompress
    if(pressio_compressor_decompress(compressor, compressed, decompressed)) {
        printf("decompression error: %s\n", pressio_compressor_error_msg(compressor));
        exit(1);
    }

    //get a pointer to the data, and it's size in bytes;
    size_t size;
    int8_t* data = pressio_data_ptr(decompressed, &size);
    printf("size of decompressed %zd\n", size);

    pressio_data_free(input);
    pressio_data_free(decompressed);
    pressio_data_free(compressed);
    pressio_compressor_release(compressor);
    pressio_release(library);

}

To install a version of LibPressio with spack spack install libpressio+sz+json and then spack load libpressio. If you prefer anaconda, conda install -c lcls-ii libpressio should also work. Installing from source shouldn't be too complicated here either.