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[examples] Clean up and comment the examples

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This commit is contained in:
Nick Terrell
2019-04-05 18:11:17 -07:00
parent 1dfe37fea9
commit 1d0c1707d1
11 changed files with 143 additions and 141 deletions
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55
examples/dictionary_decompression.c
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@ -9,15 +9,10 @@
*/
#include <stdlib.h> // malloc, exit
#include <stdio.h> // printf
#include <string.h> // strerror
#include <errno.h> // errno
#include <sys/stat.h> // stat
#define ZSTD_STATIC_LINKING_ONLY // ZSTD_findDecompressedSize
#include <stdlib.h> // free
#include <zstd.h> // presumes zstd library is installed
#include "utils.h"
#include "common.h" // Helper functions, CHECK(), and CHECK_ZSTD()
/* createDict() :
`dictFileName` is supposed to have been created using `zstd --train` */
@ -27,7 +22,7 @@ static ZSTD_DDict* createDict_orDie(const char* dictFileName)
printf("loading dictionary %s \n", dictFileName);
void* const dictBuffer = mallocAndLoadFile_orDie(dictFileName, &dictSize);
ZSTD_DDict* const ddict = ZSTD_createDDict(dictBuffer, dictSize);
if (ddict==NULL) { fprintf(stderr, "ZSTD_createDDict error \n"); exit(5); }
CHECK(ddict != NULL, "ZSTD_createDDict() failed!");
free(dictBuffer);
return ddict;
}
@ -36,24 +31,40 @@ static void decompress(const char* fname, const ZSTD_DDict* ddict)
{
size_t cSize;
void* const cBuff = mallocAndLoadFile_orDie(fname, &cSize);
unsigned long long const rSize = ZSTD_findDecompressedSize(cBuff, cSize);
if (rSize==ZSTD_CONTENTSIZE_ERROR) {
fprintf(stderr, "%s : it was not compressed by zstd.\n", fname);
exit(5);
} else if (rSize==ZSTD_CONTENTSIZE_UNKNOWN) {
fprintf(stderr, "%s : original size unknown \n", fname);
exit(6);
}
/* Read the content size from the frame header. For simplicity we require
* that it is always present. By default, zstd will write the content size
* in the header when it is known. If you can't guarantee that the frame
* content size is always written into the header, either use streaming
* decompression, or ZSTD_decompressBound().
*/
unsigned long long const rSize = ZSTD_getFrameContentSize(cBuff, cSize);
CHECK(rSize != ZSTD_CONTENTSIZE_ERROR, "%s: not compressed by zstd!", fname);
CHECK(rSize != ZSTD_CONTENTSIZE_UNKNOWN, "%s: original size unknown!", fname);
void* const rBuff = malloc_orDie((size_t)rSize);
/* Check that the dictionary ID matches.
* If a non-zstd dictionary is used, then both will be zero.
* By default zstd always writes the dictionary ID into the frame.
* Zstd will check if there is a dictionary ID mismatch as well.
*/
unsigned const expectedDictID = ZSTD_getDictID_fromDDict(ddict);
unsigned const actualDictID = ZSTD_getDictID_fromFrame(cBuff, cSize);
CHECK(actualDictID == expectedDictID,
"DictID mismatch: expected %u got %u",
expectedDictID,
actualDictID);
/* Decompress using the dictionary.
* If you need to control the decompression parameters, then use the
* advanced API: ZSTD_DCtx_setParameter(), ZSTD_DCtx_refDDict(), and
* ZSTD_decompressDCtx().
*/
ZSTD_DCtx* const dctx = ZSTD_createDCtx();
if (dctx==NULL) { fprintf(stderr, "ZSTD_createDCtx() error \n"); exit(10); }
CHECK(dctx != NULL, "ZSTD_createDCtx() failed!");
size_t const dSize = ZSTD_decompress_usingDDict(dctx, rBuff, rSize, cBuff, cSize, ddict);
if (dSize != rSize) {
fprintf(stderr, "error decoding %s : %s \n", fname, ZSTD_getErrorName(dSize));
exit(7);
}
CHECK_ZSTD(dSize);
/* When zstd knows the content size, it will error if it doesn't match. */
CHECK(dSize == rSize, "Impossible because zstd will check this condition!");
/* success */
printf("%25s : %6u -> %7u \n", fname, (unsigned)cSize, (unsigned)rSize);