From: Yann Collet Date: Fri, 2 Feb 2018 01:07:27 +0000 (-0800) Subject: clarified comments on LDM parameters X-Git-Tag: v1.3.4~1^2~60^2~9 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4b6a94f0ccb3de6ba0ff3b840febecefb6285d81;p=thirdparty%2Fzstd.git clarified comments on LDM parameters --- diff --git a/lib/zstd.h b/lib/zstd.h index be73d25b4..c3630eb00 100644 --- a/lib/zstd.h +++ b/lib/zstd.h @@ -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; diff --git a/programs/fileio.c b/programs/fileio.c index 4e5d7c411..8bfdc20ee 100644 --- a/programs/fileio.c +++ b/programs/fileio.c @@ -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 */