clarified comments on LDM parameters

diff --git a/lib/zstd.h b/lib/zstd.h
index be73d25b4251d2d89ac000646214b5000f4d42bd..c3630eb0010f7e2d6afb7f1b7690b46cadc9249a 100644 (file)
--- 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 4e5d7c4116671a9cedff01d65d0f4baad6be7084..8bfdc20ee0d26e42d68c008e292fd6eaf08b737f 100644 (file)
--- 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 */