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clarified comments on LDM parameters

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This commit is contained in:
Yann Collet 2018-02-01 17:07:27 -08:00
parent 60fa90b6c0
commit 4b6a94f0cc
2 changed files with 23 additions and 20 deletions
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34
lib/zstd.h
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@ -1015,7 +1015,7 @@ typedef enum {
/* advanced parameters - may not remain available after API update */
ZSTD_p_forceMaxWindow=1100, /* Force back-reference distances to remain < windowSize,
* even when referencing into Dictionary content (default:0) */
ZSTD_p_enableLongDistanceMatching=1200, /* Enable long distance matching.
ZSTD_p_enableLongDistanceMatching=1200, /* Enable long distance matching.
* This parameter is designed to improve the compression
* ratio for large inputs with long distance matches.
* This increases the memory usage as well as window size.
@ -1025,25 +1025,29 @@ typedef enum {
* other LDM parameters. Setting the compression level
* after this parameter overrides the window log, though LDM
* will remain enabled until explicitly disabled. */
ZSTD_p_ldmHashLog, /* Size of the table for long distance matching, as a power of 2.
* Larger values increase memory usage and compression ratio, but decrease
* compression speed.
* Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX
* (default: windowlog - 7). */
ZSTD_p_ldmMinMatch, /* Minimum size of searched matches for long distance matcher.
* Larger/too small values usually decrease compression ratio.
* Must be clamped between ZSTD_LDM_MINMATCH_MIN
* and ZSTD_LDM_MINMATCH_MAX (default: 64). */
ZSTD_p_ldmBucketSizeLog, /* Log size of each bucket in the LDM hash table for collision resolution.
* Larger values usually improve collision resolution but may decrease
* compression speed.
* The maximum value is ZSTD_LDM_BUCKETSIZELOG_MAX (default: 3). */
ZSTD_p_ldmHashLog, /* Size of the table for long distance matching, as a power of 2.
* Larger values increase memory usage and compression ratio, but decrease
* compression speed.
* Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX
* (default: windowlog - 7).
* Special: value 0 means "do not change ldmHashLog". */
ZSTD_p_ldmMinMatch, /* Minimum size of searched matches for long distance matcher.
* Larger/too small values usually decrease compression ratio.
* Must be clamped between ZSTD_LDM_MINMATCH_MIN
* and ZSTD_LDM_MINMATCH_MAX (default: 64).
* Special: value 0 means "do not change ldmMinMatch". */
ZSTD_p_ldmBucketSizeLog, /* Log size of each bucket in the LDM hash table for collision resolution.
* Larger values usually improve collision resolution but may decrease
* compression speed.
* The maximum value is ZSTD_LDM_BUCKETSIZELOG_MAX (default: 3).
* note : 0 is a valid value */
ZSTD_p_ldmHashEveryLog, /* Frequency of inserting/looking up entries in the LDM hash table.
* The default is MAX(0, (windowLog - ldmHashLog)) to
* optimize hash table usage.
* Larger values improve compression speed. Deviating far from the
* default value will likely result in a decrease in compression ratio.
* Must be clamped between 0 and ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN. */
* Must be clamped between 0 and ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN.
* note : 0 is a valid value */
} ZSTD_cParameter;

9
programs/fileio.c
View File

@ -430,7 +430,7 @@ static cRess_t FIO_createCResources(const char* dictFileName, int cLevel,
if (!ress.srcBuffer || !ress.dstBuffer)
EXM_THROW(31, "allocation error : not enough memory");
/* Advances parameters, including dictionary */
/* Advanced parameters, including dictionary */
{ void* dictBuffer;
size_t const dictBuffSize = FIO_createDictBuffer(&dictBuffer, dictFileName); /* works with dictFileName==NULL */
if (dictFileName && (dictBuffer==NULL))
@ -442,8 +442,7 @@ static cRess_t FIO_createCResources(const char* dictFileName, int cLevel,
/* compression level */
CHECK( ZSTD_CCtx_setParameter(ress.cctx, ZSTD_p_compressionLevel, cLevel) );
/* long distance matching */
CHECK( ZSTD_CCtx_setParameter(
ress.cctx, ZSTD_p_enableLongDistanceMatching, g_ldmFlag) );
CHECK( ZSTD_CCtx_setParameter(ress.cctx, ZSTD_p_enableLongDistanceMatching, g_ldmFlag) );
CHECK( ZSTD_CCtx_setParameter(ress.cctx, ZSTD_p_ldmHashLog, g_ldmHashLog) );
CHECK( ZSTD_CCtx_setParameter(ress.cctx, ZSTD_p_ldmMinMatch, g_ldmMinMatch) );
if (g_ldmBucketSizeLog != FIO_LDM_PARAM_NOTSET) {
@ -461,13 +460,13 @@ static cRess_t FIO_createCResources(const char* dictFileName, int cLevel,
CHECK( ZSTD_CCtx_setParameter(ress.cctx, ZSTD_p_targetLength, comprParams->targetLength) );
CHECK( ZSTD_CCtx_setParameter(ress.cctx, ZSTD_p_compressionStrategy, (U32)comprParams->strategy) );
/* multi-threading */
#ifdef ZSTD_MULTITHREAD
DISPLAYLEVEL(5,"set nb threads = %u \n", g_nbThreads);
CHECK( ZSTD_CCtx_setParameter(ress.cctx, ZSTD_p_nbThreads, g_nbThreads) );
#ifdef ZSTD_MULTITHREAD
CHECK( ZSTD_CCtx_setParameter(ress.cctx, ZSTD_p_nonBlockingMode, 1) );
#endif
/* dictionary */
CHECK( ZSTD_CCtx_setPledgedSrcSize(ress.cctx, srcSize) ); /* just for dictionary loading, for compression parameters adaptation */
CHECK( ZSTD_CCtx_setPledgedSrcSize(ress.cctx, srcSize) ); /* set the value temporarily for dictionary loading, to adapt compression parameters */
CHECK( ZSTD_CCtx_loadDictionary(ress.cctx, dictBuffer, dictBuffSize) );
CHECK( ZSTD_CCtx_setPledgedSrcSize(ress.cctx, ZSTD_CONTENTSIZE_UNKNOWN) ); /* reset */