zstd Interfaces

Interface Description

Optimized zstd interfaces.

Interface Format

Compression interface:

size_t ZSTD_compress2(ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);

Decompression interface:

size_t ZSTD_decompress(void* dst, size_t dstCapacity, const void* src, size_t compressedSize);

Parameters

**Table 1** Parameters of the compression interface
Parameter	Type	Description	Input/Output
cctx	Structure pointer	Initialization parameter information of the content to be compressed. (The ZSTD_createCCTX() function of the open source zstd is used for initialization. The ZSTD_CCtx_setParameter() function is used to assign values to parameters. For details, see the zstd.h header file.)	Input
dst	Pointer array	Destination array that stores the compressed content.	Input/Output
dstCapacity	Integer	Number of bytes of the compressed content.	Input
src	Pointer array	Source array that stores the content to be compressed.	Input
srcSize	Integer	Number of bytes of the content to be compressed.	Input
ret	Integer	If the operation succeeds, the number of bytes after compression is returned. Otherwise, an error code is returned.	Output

**Table 2** Parameters of the decompression interface
Parameter	Type	Description	Input/Output
dst	Pointer array	Destination array that stores the decompressed content.	Input/Output
dstCapacity	Integer	Upper limit of the number of bytes of the decompressed content.	Input
src	Pointer array	Source array that stores the content to be decompressed.	Input
compressedSize	Integer	Number of bytes of the content to be decompressed.	Input
ret	Integer	If the operation succeeds, the number of bytes of the source content after decompression is returned. Otherwise, an error code is returned.	Output

Dependency

zstd.h

Before using the interfaces, compile and deploy the complete libzstd.so dynamic library. For details, see Compiling and Installing the KSAL zstd Algorithm Package.

Example

Write zstd test code.

Create a test.c file.
```
vi test.c
```

Press i to enter the insert mode and add the following test code to the file:

#include <stdint.h>
#include <stdio.h>
#include <assert.h>
#include <string.h>
#include "/usr/ksal_zstd/zstd.h"

#define BLOCK_SIZE (128 * 1024)
#define DST_SIZE (1024 * 1024)

uint8_t inn[BLOCK_SIZE]={0};
uint8_t outt[DST_SIZE];
uint8_t doutt[DST_SIZE];

int main(int argc, char **argv)
{
    ZSTD_CCtx *cctx = ZSTD_createCCtx();
    ZSTD_CCtx_setParameter(cctx, ZSTD_c_compressionLevel, 5);
	
    size_t compressed = ZSTD_compress2(cctx, (void *)outt, DST_SIZE, (void *)inn, BLOCK_SIZE);
    size_t decompressed = ZSTD_decompress(doutt, DST_SIZE, outt, compressed);
	
    assert(decompressed == BLOCK_SIZE);
    assert(memcmp(doutt, inn, BLOCK_SIZE) == 0);

    ZSTD_freeCCtx(cctx);
    printf("compression and decompression succ!!\n");
    return 0;
}

Press Esc to exit the insert mode. Type :wq! and press Enter to save and exit the file.

Compile the test.c file into an executable file test.
```
gcc test.c -L/usr/ksal_zstd -l:libzstd.so -o test
```

Run the test executable file.

LD_PRELOAD=/usr/ksal_zstd/libzstd.so ./test

The command output is as follows:

compression and decompression succ!!

Parent topic: KSAL Development Reference