Merge branch 'dev' into BD_deterministic

11 files changed, 152 insertions, 49 deletions

diff --git a/doc/lz4_manual.html b/doc/lz4_manual.html
index f8639fe..ddd2724 100644
--- a/doc/lz4_manual.html
+++ b/doc/lz4_manual.html
@@ -126,15 +126,17 @@ int LZ4_compress_fast_extState (void* state, const char* src, char* dst, int src
 
 <pre><b>int LZ4_decompress_fast (const char* src, char* dst, int originalSize);
 </b><p>This function is a bit faster than LZ4_decompress_safe(),
-but doesn't provide any security guarantee.
+but it may misbehave on malformed input because it doesn't perform full validation of compressed data.
     originalSize : is the uncompressed size to regenerate
                    Destination buffer must be already allocated, and its size must be >= 'originalSize' bytes.
     return : number of bytes read from source buffer (== compressed size).
              If the source stream is detected malformed, the function stops decoding and return a negative result.
-    note : This function respects memory boundaries for *properly formed* compressed data.
-           However, it does not provide any protection against malicious input.
-           It also doesn't know 'src' size, and implies it's >= compressed size.
-           Use this function in trusted environment **only**.
+    note : This function is only usable if the originalSize of uncompressed data is known in advance.
+           The caller should also check that all the compressed input has been consumed properly,
+           i.e. that the return value matches the size of the buffer with compressed input.
+           The function never writes past the output buffer.  However, since it doesn't know its 'src' size,
+           it may read past the intended input.  Also, because match offsets are not validated during decoding,
+           reads from 'src' may underflow.  Use this function in trusted environment **only**.
 </p></pre><BR>
 
 <pre><b>int LZ4_decompress_safe_partial (const char* src, char* dst, int srcSize, int targetOutputSize, int dstCapacity);
diff --git a/doc/lz4frame_manual.html b/doc/lz4frame_manual.html
index 459bac8..53ea7eb 100644
--- a/doc/lz4frame_manual.html
+++ b/doc/lz4frame_manual.html
@@ -18,6 +18,7 @@
 <li><a href="#Chapter8">Compression</a></li>
 <li><a href="#Chapter9">Decompression functions</a></li>
 <li><a href="#Chapter10">Streaming decompression functions</a></li>
+<li><a href="#Chapter11">Bulk processing dictionary API</a></li>
 </ol>
 <hr>
 <a name="Chapter1"></a><h2>Introduction</h2><pre>
@@ -89,12 +90,13 @@
 
 <pre><b>typedef struct {
   LZ4F_frameInfo_t frameInfo;
-  int      compressionLevel;       </b>/* 0: default (fast mode); values > LZ4HC_CLEVEL_MAX count as LZ4HC_CLEVEL_MAX; values < 0 trigger "fast acceleration" */<b>
-  unsigned autoFlush;              </b>/* 1 == always flush, to reduce usage of internal buffers */<b>
-  unsigned reserved[4];            </b>/* must be zero for forward compatibility */<b>
+  int      compressionLevel;    </b>/* 0: default (fast mode); values > LZ4HC_CLEVEL_MAX count as LZ4HC_CLEVEL_MAX; values < 0 trigger "fast acceleration" */<b>
+  unsigned autoFlush;           </b>/* 1: always flush, to reduce usage of internal buffers */<b>
+  unsigned favorDecSpeed;       </b>/* 1: parser favors decompression speed vs compression ratio. Only works for high compression modes (>= LZ4LZ4HC_CLEVEL_OPT_MIN) */  /* >= v1.8.2 */<b>
+  unsigned reserved[3];         </b>/* must be zero for forward compatibility */<b>
 } LZ4F_preferences_t;
 </b><p>  makes it possible to supply detailed compression parameters to the stream interface.
-  It's not required to set all fields, as long as the structure was initially memset() to zero.
+  Structure is presumed initially memset() to zero, representing default settings.
   All reserved fields must be set to zero. 
 </p></pre><BR>
 
@@ -293,5 +295,58 @@ LZ4F_errorCode_t LZ4F_freeDecompressionContext(LZ4F_dctx* dctx);
   and start a new one using same context resources. 
 </p></pre><BR>
 
+<pre><b>typedef enum { LZ4F_LIST_ERRORS(LZ4F_GENERATE_ENUM) } LZ4F_errorCodes;
+</b></pre><BR>
+<a name="Chapter11"></a><h2>Bulk processing dictionary API</h2><pre></pre>
+
+<pre><b>LZ4FLIB_STATIC_API LZ4F_CDict* LZ4F_createCDict(const void* dictBuffer, size_t dictSize);
+LZ4FLIB_STATIC_API void        LZ4F_freeCDict(LZ4F_CDict* CDict);
+</b><p>  When compressing multiple messages / blocks with the same dictionary, it's recommended to load it just once.
+  LZ4_createCDict() will create a digested dictionary, ready to start future compression operations without startup delay.
+  LZ4_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only.
+ `dictBuffer` can be released after LZ4_CDict creation, since its content is copied within CDict 
+</p></pre><BR>
+
+<pre><b>LZ4FLIB_STATIC_API size_t LZ4F_compressFrame_usingCDict(
+    LZ4F_cctx* cctx,
+    void* dst, size_t dstCapacity,
+    const void* src, size_t srcSize,
+    const LZ4F_CDict* cdict,
+    const LZ4F_preferences_t* preferencesPtr);
+</b><p>  Compress an entire srcBuffer into a valid LZ4 frame using a digested Dictionary.
+  cctx must point to a context created by LZ4F_createCompressionContext().
+  If cdict==NULL, compress without a dictionary.
+  dstBuffer MUST be >= LZ4F_compressFrameBound(srcSize, preferencesPtr).
+  If this condition is not respected, function will fail (@return an errorCode).
+  The LZ4F_preferences_t structure is optional : you may provide NULL as argument,
+  but it's not recommended, as it's the only way to provide dictID in the frame header.
+ @return : number of bytes written into dstBuffer.
+           or an error code if it fails (can be tested using LZ4F_isError()) 
+</p></pre><BR>
+
+<pre><b>LZ4FLIB_STATIC_API size_t LZ4F_compressBegin_usingCDict(
+    LZ4F_cctx* cctx,
+    void* dstBuffer, size_t dstCapacity,
+    const LZ4F_CDict* cdict,
+    const LZ4F_preferences_t* prefsPtr);
+</b><p>  Inits streaming dictionary compression, and writes the frame header into dstBuffer.
+  dstCapacity must be >= LZ4F_HEADER_SIZE_MAX bytes.
+ `prefsPtr` is optional : you may provide NULL as argument,
+  however, it's the only way to provide dictID in the frame header.
+ @return : number of bytes written into dstBuffer for the header,
+           or an error code (which can be tested using LZ4F_isError()) 
+</p></pre><BR>
+
+<pre><b>LZ4FLIB_STATIC_API size_t LZ4F_decompress_usingDict(
+    LZ4F_dctx* dctxPtr,
+    void* dstBuffer, size_t* dstSizePtr,
+    const void* srcBuffer, size_t* srcSizePtr,
+    const void* dict, size_t dictSize,
+    const LZ4F_decompressOptions_t* decompressOptionsPtr);
+</b><p>  Same as LZ4F_decompress(), using a predefined dictionary.
+  Dictionary is used "in place", without any preprocessing.
+  It must remain accessible throughout the entire frame decoding. 
+</p></pre><BR>
+
 </html>
 </body>
diff --git a/examples/frameCompress.c b/examples/frameCompress.c
index 972f716..9bfea48 100644
--- a/examples/frameCompress.c
+++ b/examples/frameCompress.c
@@ -21,7 +21,8 @@ static const LZ4F_preferences_t kPrefs = {
       0 /* unknown content size */, 0 /* no dictID */ , LZ4F_noBlockChecksum },
     0,   /* compression level; 0 == default */
     0,   /* autoflush */
-    { 0, 0, 0, 0 },  /* reserved, must be set to 0 */
+    0,   /* favor decompression speed */
+    { 0, 0, 0 },  /* reserved, must be set to 0 */
 };
 
 
diff --git a/lib/lz4.c b/lib/lz4.c
index b4d3140..06ff611 100644
--- a/lib/lz4.c
+++ b/lib/lz4.c
@@ -161,11 +161,11 @@
 *  Memory routines
 **************************************/
 #include <stdlib.h>   /* malloc, calloc, free */
-#define ALLOC(s) malloc(s)
+#define ALLOC(s)          malloc(s)
 #define ALLOC_AND_ZERO(s) calloc(1,s)
-#define FREEMEM        free
+#define FREEMEM(p)        free(p)
 #include <string.h>   /* memset, memcpy */
-#define MEM_INIT       memset
+#define MEM_INIT(p,v,s)   memset((p),(v),(s))
 
 
 /*-************************************
diff --git a/lib/lz4frame.c b/lib/lz4frame.c
index 4d6d39c..93ce696 100644
--- a/lib/lz4frame.c
+++ b/lib/lz4frame.c
@@ -612,6 +612,9 @@ size_t LZ4F_compressBegin_usingCDict(LZ4F_cctx* cctxPtr,
         /* frame init only for blockLinked : blockIndependent will be init at each block */
         LZ4F_applyCDict(cctxPtr->lz4CtxPtr, cdict, cctxPtr->prefs.compressionLevel);
     }
+    if (preferencesPtr->compressionLevel >= LZ4HC_CLEVEL_MIN) {
+          LZ4_favorDecompressionSpeed((LZ4_streamHC_t*)cctxPtr->lz4CtxPtr, (int)preferencesPtr->favorDecSpeed);
+    }
 
     /* Magic Number */
     LZ4F_writeLE32(dstPtr, LZ4F_MAGICNUMBER);
diff --git a/lib/lz4frame.h b/lib/lz4frame.h
index bd715bd..fb434ff 100644
--- a/lib/lz4frame.h
+++ b/lib/lz4frame.h
@@ -173,13 +173,14 @@ typedef struct {
 
 /*! LZ4F_preferences_t :
  *  makes it possible to supply detailed compression parameters to the stream interface.
- *  It's not required to set all fields, as long as the structure was initially memset() to zero.
+ *  Structure is presumed initially memset() to zero, representing default settings.
  *  All reserved fields must be set to zero. */
 typedef struct {
   LZ4F_frameInfo_t frameInfo;
-  int      compressionLevel;       /* 0: default (fast mode); values > LZ4HC_CLEVEL_MAX count as LZ4HC_CLEVEL_MAX; values < 0 trigger "fast acceleration" */
-  unsigned autoFlush;              /* 1 == always flush, to reduce usage of internal buffers */
-  unsigned reserved[4];            /* must be zero for forward compatibility */
+  int      compressionLevel;    /* 0: default (fast mode); values > LZ4HC_CLEVEL_MAX count as LZ4HC_CLEVEL_MAX; values < 0 trigger "fast acceleration" */
+  unsigned autoFlush;           /* 1: always flush, to reduce usage of internal buffers */
+  unsigned favorDecSpeed;       /* 1: parser favors decompression speed vs compression ratio. Only works for high compression modes (>= LZ4LZ4HC_CLEVEL_OPT_MIN) */  /* >= v1.8.2 */
+  unsigned reserved[3];         /* must be zero for forward compatibility */
 } LZ4F_preferences_t;
 
 LZ4FLIB_API int LZ4F_compressionLevel_max(void);
diff --git a/lib/lz4hc.c b/lib/lz4hc.c
index 184ca8c..f2dc21b 100644
--- a/lib/lz4hc.c
+++ b/lib/lz4hc.c
@@ -200,6 +200,7 @@ LZ4HC_reverseCountPattern(const BYTE* ip, const BYTE* const iLow, U32 pattern)
 }
 
 typedef enum { rep_untested, rep_not, rep_confirmed } repeat_state_e;
+typedef enum { favorCompressionRatio=0, favorDecompressionSpeed } HCfavor_e;
 
 LZ4_FORCE_INLINE int
 LZ4HC_InsertAndGetWiderMatch (
@@ -212,7 +213,8 @@ LZ4HC_InsertAndGetWiderMatch (
     const BYTE** startpos,
     const int maxNbAttempts,
     const int patternAnalysis,
-    const dictCtx_directive dict)
+    const dictCtx_directive dict,
+    const HCfavor_e favorDecSpeed)
 {
     U16* const chainTable = hc4->chainTable;
     U32* const HashTable = hc4->hashTable;
@@ -241,7 +243,10 @@ LZ4HC_InsertAndGetWiderMatch (
     while ((matchIndex>=lowLimit) && (nbAttempts)) {
         DEBUGLOG(7, "remaining attempts : %i", nbAttempts);
         nbAttempts--;
-        if (matchIndex >= dictLimit) {
+        assert(matchIndex < ipIndex);
+        if (favorDecSpeed && (ipIndex - matchIndex < 8)) {
+            /* do nothing */
+        } else if (matchIndex >= dictLimit) {
             const BYTE* const matchPtr = base + matchIndex;
             assert(matchPtr >= lowPrefixPtr);
             assert(matchPtr < ip);
@@ -328,14 +333,12 @@ LZ4HC_InsertAndGetWiderMatch (
                 }
             }
 
-            {
-                U32 const nextOffset = DELTANEXTU16(dictCtx->chainTable, dictMatchIndex);
+            {   U32 const nextOffset = DELTANEXTU16(dictCtx->chainTable, dictMatchIndex);
                 dictMatchIndex -= nextOffset;
                 matchIndex -= nextOffset;
             }
         }
     }
-
     return longest;
 }
 
@@ -351,7 +354,7 @@ int LZ4HC_InsertAndFindBestMatch(LZ4HC_CCtx_internal* const hc4,   /* Index tabl
     /* note : LZ4HC_InsertAndGetWiderMatch() is able to modify the starting position of a match (*startpos),
      * but this won't be the case here, as we define iLowLimit==ip,
      * so LZ4HC_InsertAndGetWiderMatch() won't be allowed to search past ip */
-    return LZ4HC_InsertAndGetWiderMatch(hc4, ip, ip, iLimit, MINMATCH-1, matchpos, &uselessPtr, maxNbAttempts, patternAnalysis, dict);
+    return LZ4HC_InsertAndGetWiderMatch(hc4, ip, ip, iLimit, MINMATCH-1, matchpos, &uselessPtr, maxNbAttempts, patternAnalysis, dict, favorCompressionRatio);
 }
 
 
@@ -484,7 +487,7 @@ _Search2:
         if (ip+ml <= mflimit) {
             ml2 = LZ4HC_InsertAndGetWiderMatch(ctx,
                             ip + ml - 2, ip + 0, matchlimit, ml, &ref2, &start2,
-                            maxNbAttempts, patternAnalysis, dict);
+                            maxNbAttempts, patternAnalysis, dict, favorCompressionRatio);
         } else {
             ml2 = ml;
         }
@@ -529,7 +532,7 @@ _Search3:
         if (start2 + ml2 <= mflimit) {
             ml3 = LZ4HC_InsertAndGetWiderMatch(ctx,
                             start2 + ml2 - 3, start2, matchlimit, ml2, &ref3, &start3,
-                            maxNbAttempts, patternAnalysis, dict);
+                            maxNbAttempts, patternAnalysis, dict, favorCompressionRatio);
         } else {
             ml3 = ml2;
         }
@@ -650,12 +653,14 @@ _dest_overflow:
     return 0;
 }
 
+
 static int LZ4HC_compress_optimal( LZ4HC_CCtx_internal* ctx,
     const char* const source, char* dst,
     int* srcSizePtr, int dstCapacity,
     int const nbSearches, size_t sufficient_len,
     const limitedOutput_directive limit, int const fullUpdate,
-    const dictCtx_directive dict);
+    const dictCtx_directive dict,
+    HCfavor_e favorDecSpeed);
 
 
 LZ4_FORCE_INLINE int LZ4HC_compress_generic_internal (
@@ -700,6 +705,7 @@ LZ4_FORCE_INLINE int LZ4HC_compress_generic_internal (
     if (cLevel < 1) cLevel = LZ4HC_CLEVEL_DEFAULT;   /* note : convention is different from lz4frame, maybe something to review */
     cLevel = MIN(LZ4HC_CLEVEL_MAX, cLevel);
     {   cParams_t const cParam = clTable[cLevel];
+        HCfavor_e const favor = ctx->favorDecSpeed ? favorDecompressionSpeed : favorCompressionRatio;
         if (cParam.strat == lz4hc)
             return LZ4HC_compress_hashChain(ctx,
                                 src, dst, srcSizePtr, dstCapacity,
@@ -708,7 +714,8 @@ LZ4_FORCE_INLINE int LZ4HC_compress_generic_internal (
         return LZ4HC_compress_optimal(ctx,
                             src, dst, srcSizePtr, dstCapacity,
                             cParam.nbSearches, cParam.targetLength, limit,
-                            cLevel == LZ4HC_CLEVEL_MAX, dict);  /* ultra mode */
+                            cLevel == LZ4HC_CLEVEL_MAX,   /* ultra mode */
+                            dict, favor);
     }
 }
 
@@ -746,7 +753,7 @@ static int LZ4HC_compress_generic_dictCtx (
     } else if (position == 0 && *srcSizePtr > 4 KB) {
         memcpy(ctx, ctx->dictCtx, sizeof(LZ4HC_CCtx_internal));
         LZ4HC_setExternalDict(ctx, (const BYTE *)src);
-        ctx->compressionLevel = cLevel;
+        ctx->compressionLevel = (short)cLevel;
         return LZ4HC_compress_generic_noDictCtx(ctx, src, dst, srcSizePtr, dstCapacity, cLevel, limit);
     } else {
         return LZ4HC_compress_generic_internal(ctx, src, dst, srcSizePtr, dstCapacity, cLevel, limit, usingDictCtx);
@@ -795,7 +802,7 @@ int LZ4_compress_HC_extStateHC (void* state, const char* src, char* dst, int src
 int LZ4_compress_HC(const char* src, char* dst, int srcSize, int dstCapacity, int compressionLevel)
 {
 #if defined(LZ4HC_HEAPMODE) && LZ4HC_HEAPMODE==1
-    LZ4_streamHC_t* const statePtr = (LZ4_streamHC_t*)malloc(sizeof(LZ4_streamHC_t));
+    LZ4_streamHC_t* const statePtr = (LZ4_streamHC_t*)ALLOC(sizeof(LZ4_streamHC_t));
 #else
     LZ4_streamHC_t state;
     LZ4_streamHC_t* const statePtr = &state;
@@ -824,10 +831,9 @@ int LZ4_compress_HC_destSize(void* LZ4HC_Data, const char* source, char* dest, i
 **************************************/
 /* allocation */
 LZ4_streamHC_t* LZ4_createStreamHC(void) {
-    LZ4_streamHC_t* LZ4_streamHCPtr = (LZ4_streamHC_t*)malloc(sizeof(LZ4_streamHC_t));
-    LZ4_streamHCPtr->internal_donotuse.end = (const BYTE *)(ptrdiff_t)-1;
-    LZ4_streamHCPtr->internal_donotuse.base = NULL;
-    LZ4_streamHCPtr->internal_donotuse.dictCtx = NULL;
+    LZ4_streamHC_t* const LZ4_streamHCPtr = (LZ4_streamHC_t*)ALLOC(sizeof(LZ4_streamHC_t));
+    if (LZ4_streamHCPtr==NULL) return NULL;
+    LZ4_resetStreamHC(LZ4_streamHCPtr, LZ4HC_CLEVEL_DEFAULT);
     return LZ4_streamHCPtr;
 }
 
@@ -847,6 +853,7 @@ void LZ4_resetStreamHC (LZ4_streamHC_t* LZ4_streamHCPtr, int compressionLevel)
     LZ4_streamHCPtr->internal_donotuse.end = (const BYTE *)(ptrdiff_t)-1;
     LZ4_streamHCPtr->internal_donotuse.base = NULL;
     LZ4_streamHCPtr->internal_donotuse.dictCtx = NULL;
+    LZ4_streamHCPtr->internal_donotuse.favorDecSpeed = 0;
     LZ4_setCompressionLevel(LZ4_streamHCPtr, compressionLevel);
 }
 
@@ -863,7 +870,12 @@ void LZ4_setCompressionLevel(LZ4_streamHC_t* LZ4_streamHCPtr, int compressionLev
 {
     if (compressionLevel < 1) compressionLevel = LZ4HC_CLEVEL_DEFAULT;
     if (compressionLevel > LZ4HC_CLEVEL_MAX) compressionLevel = LZ4HC_CLEVEL_MAX;
-    LZ4_streamHCPtr->internal_donotuse.compressionLevel = compressionLevel;
+    LZ4_streamHCPtr->internal_donotuse.compressionLevel = (short)compressionLevel;
+}
+
+void LZ4_favorDecompressionSpeed(LZ4_streamHC_t* LZ4_streamHCPtr, int favor)
+{
+    LZ4_streamHCPtr->internal_donotuse.favorDecSpeed = (favor!=0);
 }
 
 int LZ4_loadDictHC (LZ4_streamHC_t* LZ4_streamHCPtr, const char* dictionary, int dictSize)
@@ -1080,23 +1092,26 @@ LZ4_FORCE_INLINE LZ4HC_match_t
 LZ4HC_FindLongerMatch(LZ4HC_CCtx_internal* const ctx,
                       const BYTE* ip, const BYTE* const iHighLimit,
                       int minLen, int nbSearches,
-                      const dictCtx_directive dict)
+                      const dictCtx_directive dict,
+                      const HCfavor_e favorDecSpeed)
 {
     LZ4HC_match_t match = { 0 , 0 };
     const BYTE* matchPtr = NULL;
     /* note : LZ4HC_InsertAndGetWiderMatch() is able to modify the starting position of a match (*startpos),
      * but this won't be the case here, as we define iLowLimit==ip,
      * so LZ4HC_InsertAndGetWiderMatch() won't be allowed to search past ip */
-    int const matchLength = LZ4HC_InsertAndGetWiderMatch(ctx,
+    int matchLength = LZ4HC_InsertAndGetWiderMatch(ctx,
                                 ip, ip, iHighLimit, minLen, &matchPtr, &ip,
-                                nbSearches, 1 /* patternAnalysis */, dict);
+                                nbSearches, 1 /* patternAnalysis */, dict, favorDecSpeed);
     if (matchLength <= minLen) return match;
+    if (favorDecSpeed) {
+        if ((matchLength>18) & (matchLength<=36)) matchLength=18;   /* favor shortcut */
+    }
     match.len = matchLength;
     match.off = (int)(ip-matchPtr);
     return match;
 }
 
-
 static int LZ4HC_compress_optimal (
     LZ4HC_CCtx_internal* ctx,
     const char* const source,
@@ -1107,7 +1122,8 @@ static int LZ4HC_compress_optimal (
     size_t sufficient_len,
     const limitedOutput_directive limit,
     int const fullUpdate,
-    const dictCtx_directive dict
+    const dictCtx_directive dict,
+    const HCfavor_e favorDecSpeed
     )
 {
 #define TRAILING_LITERALS 3
@@ -1135,7 +1151,7 @@ static int LZ4HC_compress_optimal (
          int best_mlen, best_off;
          int cur, last_match_pos = 0;
 
-         LZ4HC_match_t const firstMatch = LZ4HC_FindLongerMatch(ctx, ip, matchlimit, MINMATCH-1, nbSearches, dict);
+         LZ4HC_match_t const firstMatch = LZ4HC_FindLongerMatch(ctx, ip, matchlimit, MINMATCH-1, nbSearches, dict, favorDecSpeed);
          if (firstMatch.len==0) { ip++; continue; }
 
          if ((size_t)firstMatch.len > sufficient_len) {
@@ -1205,10 +1221,10 @@ static int LZ4HC_compress_optimal (
 
              DEBUGLOG(7, "search at rPos:%u", cur);
              if (fullUpdate)
-                 newMatch = LZ4HC_FindLongerMatch(ctx, curPtr, matchlimit, MINMATCH-1, nbSearches, dict);
+                 newMatch = LZ4HC_FindLongerMatch(ctx, curPtr, matchlimit, MINMATCH-1, nbSearches, dict, favorDecSpeed);
              else
                  /* only test matches of minimum length; slightly faster, but misses a few bytes */
-                 newMatch = LZ4HC_FindLongerMatch(ctx, curPtr, matchlimit, last_match_pos - cur, nbSearches, dict);
+                 newMatch = LZ4HC_FindLongerMatch(ctx, curPtr, matchlimit, last_match_pos - cur, nbSearches, dict, favorDecSpeed);
              if (!newMatch.len) continue;
 
              if ( ((size_t)newMatch.len > sufficient_len)
@@ -1256,7 +1272,9 @@ static int LZ4HC_compress_optimal (
                          price = opt[cur].price + LZ4HC_sequencePrice(0, ml);
                      }
 
-                     if (pos > last_match_pos+TRAILING_LITERALS || price <= opt[pos].price) {
+                    assert((U32)favorDecSpeed <= 1);
+                     if (pos > last_match_pos+TRAILING_LITERALS
+                      || price <= opt[pos].price - (int)favorDecSpeed) {
                          DEBUGLOG(7, "rPos:%3i => price:%3i (matchlen=%i)",
                                      pos, price, ml);
                          assert(pos < LZ4_OPT_NUM);
diff --git a/lib/lz4hc.h b/lib/lz4hc.h
index 28e2528..bb5e073 100644
--- a/lib/lz4hc.h
+++ b/lib/lz4hc.h
@@ -152,7 +152,8 @@ struct LZ4HC_CCtx_internal
     uint32_t   dictLimit;       /* below that point, need extDict */
     uint32_t   lowLimit;        /* below that point, no more dict */
     uint32_t   nextToUpdate;    /* index from which to continue dictionary update */
-    int        compressionLevel;
+    short      compressionLevel;
+    short      favorDecSpeed;
     const LZ4HC_CCtx_internal* dictCtx;
 };
 
@@ -169,7 +170,8 @@ struct LZ4HC_CCtx_internal
     unsigned int   dictLimit;        /* below that point, need extDict */
     unsigned int   lowLimit;         /* below that point, no more dict */
     unsigned int   nextToUpdate;     /* index from which to continue dictionary update */
-    int            compressionLevel;
+    short          compressionLevel;
+    short          favorDecSpeed;
     const LZ4HC_CCtx_internal* dictCtx;
 };
 
@@ -253,9 +255,9 @@ LZ4_DEPRECATED("use LZ4_resetStreamHC() instead") LZ4LIB_API  int   LZ4_resetStr
  * `srcSizePtr` : value will be updated to indicate how much bytes were read from `src`
  */
 int LZ4_compress_HC_destSize(void* LZ4HC_Data,
-                            const char* src, char* dst,
-                            int* srcSizePtr, int targetDstSize,
-                            int compressionLevel);
+                             const char* src, char* dst,
+                             int* srcSizePtr, int targetDstSize,
+                             int compressionLevel);
 
 /*! LZ4_compress_HC_continue_destSize() : v1.8.0 (experimental)
  *  Similar as LZ4_compress_HC_continue(),
@@ -275,6 +277,12 @@ int LZ4_compress_HC_continue_destSize(LZ4_streamHC_t* LZ4_streamHCPtr,
  */
 void LZ4_setCompressionLevel(LZ4_streamHC_t* LZ4_streamHCPtr, int compressionLevel);
 
+/*! LZ4_favorDecompressionSpeed() : v1.8.2 (experimental)
+ *  Parser will select decisions favoring decompression over compression ratio.
+ *  Only work at highest compression settings (level >= LZ4HC_CLEVEL_OPT_MIN)
+ */
+void LZ4_favorDecompressionSpeed(LZ4_streamHC_t* LZ4_streamHCPtr, int favor);
+
 /*! LZ4_resetStreamHC_fast() :
  *  When an LZ4_streamHC_t is known to be in a internally coherent state,
  *  it can often be prepared for a new compression with almost no work, only
diff --git a/programs/lz4cli.c b/programs/lz4cli.c
index 42392eb..ba519b4 100644
--- a/programs/lz4cli.c
+++ b/programs/lz4cli.c
@@ -140,6 +140,7 @@ static int usage_advanced(const char* exeName)
     DISPLAY( "--no-frame-crc : disable stream checksum (default:enabled) \n");
     DISPLAY( "--content-size : compressed frame includes original size (default:not present)\n");
     DISPLAY( "--[no-]sparse  : sparse mode (default:enabled on file, disabled on stdout)\n");
+    DISPLAY( "--favor-decSpeed: compressed files decompress faster, but are less compressed \n");
     DISPLAY( "Benchmark arguments : \n");
     DISPLAY( " -b#    : benchmark file(s), using # compression level (default : 1) \n");
     DISPLAY( " -e#    : test all compression levels from -bX to # (default : 1)\n");
@@ -355,6 +356,7 @@ int main(int argc, const char** argv)
                 if (!strcmp(argument,  "--no-content-size")) { LZ4IO_setContentSize(0); continue; }
                 if (!strcmp(argument,  "--sparse")) { LZ4IO_setSparseFile(2); continue; }
                 if (!strcmp(argument,  "--no-sparse")) { LZ4IO_setSparseFile(0); continue; }
+                if (!strcmp(argument,  "--favor-decSpeed")) { LZ4IO_favorDecSpeed(1); continue; }
                 if (!strcmp(argument,  "--verbose")) { displayLevel++; continue; }
                 if (!strcmp(argument,  "--quiet")) { if (displayLevel) displayLevel--; continue; }
                 if (!strcmp(argument,  "--version")) { DISPLAY(WELCOME_MESSAGE); return 0; }
diff --git a/programs/lz4io.c b/programs/lz4io.c
index ccf4fa1..b52c1f3 100644
--- a/programs/lz4io.c
+++ b/programs/lz4io.c
@@ -116,6 +116,7 @@ static int g_blockIndependence = 1;
 static int g_sparseFileSupport = 1;
 static int g_contentSizeFlag = 0;
 static int g_useDictionary = 0;
+static unsigned g_favorDecSpeed = 0;
 static const char* g_dictionaryFilename = NULL;
 
 
@@ -221,6 +222,12 @@ int LZ4IO_setContentSize(int enable)
     return g_contentSizeFlag;
 }
 
+/* Default setting : 0 (disabled) */
+void LZ4IO_favorDecSpeed(int favor)
+{
+    g_favorDecSpeed = (favor!=0);
+}
+
 static U32 g_removeSrcFile = 0;
 void LZ4IO_setRemoveSrcFile(unsigned flag) { g_removeSrcFile = (flag>0); }
 
@@ -548,6 +555,7 @@ static int LZ4IO_compressFilename_extRess(cRess_t ress, const char* srcFileName,
     prefs.frameInfo.blockSizeID = (LZ4F_blockSizeID_t)g_blockSizeId;
     prefs.frameInfo.blockChecksumFlag = (LZ4F_blockChecksum_t)g_blockChecksum;
     prefs.frameInfo.contentChecksumFlag = (LZ4F_contentChecksum_t)g_streamChecksum;
+    prefs.favorDecSpeed = g_favorDecSpeed;
     if (g_contentSizeFlag) {
       U64 const fileSize = UTIL_getFileSize(srcFileName);
       prefs.frameInfo.contentSize = fileSize;   /* == 0 if input == stdin */
diff --git a/programs/lz4io.h b/programs/lz4io.h
index b21b8b6..22c5e3e 100644
--- a/programs/lz4io.h
+++ b/programs/lz4io.h
@@ -94,10 +94,15 @@ int LZ4IO_setNotificationLevel(int level);
 /* Default setting : 0 (disabled) */
 int LZ4IO_setSparseFile(int enable);
 
-/* Default setting : 0 (disabled) */
+/* Default setting : 0 == no content size present in frame header */
 int LZ4IO_setContentSize(int enable);
 
+/* Default setting : 0 == src file preserved */
 void LZ4IO_setRemoveSrcFile(unsigned flag);
 
+/* Default setting : 0 == favor compression ratio
+ * Note : 1 only works for high compression levels (10+) */
+void LZ4IO_favorDecSpeed(int favor);
+
 
 #endif  /* LZ4IO_H_237902873 */