Merge pull request #347 from lz4/negativeCLevels

Negative Compression levels

5 files changed, 35 insertions, 22 deletions

diff --git a/NEWS b/NEWS
index 4fb8fdd..32fb613 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,7 @@ v1.7.6
 cli : fix : do not modify /dev/null permissions, reported by @Maokaman1
 cli : added GNU separator -- specifying that all following arguments are files
 API : added LZ4_compress_HC_destSize(), by Oleg (@remittor)
+API : lz4frame : negative compression levels trigger fast acceleration
 API : fix : expose obsolete decoding functions, reported by Chen Yufei
 build : dragonFlyBSD, OpenBSD, NetBSD supported
 build : LZ4_MEMORY_USAGE can be modified at compile time, through external define
diff --git a/lib/lz4.h b/lib/lz4.h
index 588de22..d5a3016 100644
--- a/lib/lz4.h
+++ b/lib/lz4.h
@@ -256,19 +256,19 @@ LZ4LIB_API int LZ4_loadDict (LZ4_stream_t* streamPtr, const char* dictionary, in
 
 /*! LZ4_compress_fast_continue() :
  *  Compress buffer content 'src', using data from previously compressed blocks as dictionary to improve compression ratio.
- *  Important : Previous data blocks are assumed to still be present and unmodified !
+ *  Important : Previous data blocks are assumed to remain present and unmodified !
  *  'dst' buffer must be already allocated.
- *  If maxDstSize >= LZ4_compressBound(srcSize), compression is guaranteed to succeed, and runs faster.
+ *  If dstCapacity >= LZ4_compressBound(srcSize), compression is guaranteed to succeed, and runs faster.
  *  If not, and if compressed data cannot fit into 'dst' buffer size, compression stops, and function returns a zero.
+ *  After an error, the stream status is invalid, and it can only be reset or freed.
  */
-LZ4LIB_API int LZ4_compress_fast_continue (LZ4_stream_t* streamPtr, const char* src, char* dst, int srcSize, int maxDstSize, int acceleration);
+LZ4LIB_API int LZ4_compress_fast_continue (LZ4_stream_t* streamPtr, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration);
 
 /*! LZ4_saveDict() :
- *  If previously compressed data block is not guaranteed to remain available at its memory location,
+ *  If previously compressed data block is not guaranteed to remain available at its current memory location,
  *  save it into a safer place (char* safeBuffer).
- *  Note : you don't need to call LZ4_loadDict() afterwards,
- *         dictionary is immediately usable, you can therefore call LZ4_compress_fast_continue().
- *  Return : saved dictionary size in bytes (necessarily <= dictSize), or 0 if error.
+ *  Note : it's not necessary to call LZ4_loadDict() after LZ4_saveDict(), dictionary is immediately usable.
+ *  @return : saved dictionary size in bytes (necessarily <= dictSize), or 0 if error.
  */
 LZ4LIB_API int LZ4_saveDict (LZ4_stream_t* streamPtr, char* safeBuffer, int dictSize);
 
diff --git a/lib/lz4frame.c b/lib/lz4frame.c
index e04fe83..356be8a 100644
--- a/lib/lz4frame.c
+++ b/lib/lz4frame.c
@@ -316,11 +316,11 @@ size_t LZ4F_compressFrame(void* dstBuffer, size_t dstCapacity, const void* srcBu
     BYTE* dstPtr = dstStart;
     BYTE* const dstEnd = dstStart + dstCapacity;
 
-    memset(&cctxI, 0, sizeof(cctxI));   /* works because no allocation */
+    memset(&cctxI, 0, sizeof(cctxI));
     memset(&options, 0, sizeof(options));
 
     cctxI.version = LZ4F_VERSION;
-    cctxI.maxBufferSize = 5 MB;   /* mess with real buffer size to prevent allocation; works because autoflush==1 & stableSrc==1 */
+    cctxI.maxBufferSize = 5 MB;   /* mess with real buffer size to prevent dynamic allocation; works because autoflush==1 & stableSrc==1 */
 
     if (preferencesPtr!=NULL)
         prefs = *preferencesPtr;
@@ -332,7 +332,7 @@ size_t LZ4F_compressFrame(void* dstBuffer, size_t dstCapacity, const void* srcBu
     if (prefs.compressionLevel < LZ4HC_CLEVEL_MIN) {
         cctxI.lz4CtxPtr = &lz4ctx;
         cctxI.lz4CtxLevel = 1;
-    }
+    }  /* otherwise : will be created within LZ4F_compressBegin */
 
     prefs.frameInfo.blockSizeID = LZ4F_optimalBSID(prefs.frameInfo.blockSizeID, srcSize);
     prefs.autoFlush = 1;
@@ -341,7 +341,7 @@ size_t LZ4F_compressFrame(void* dstBuffer, size_t dstCapacity, const void* srcBu
 
     options.stableSrc = 1;
 
-    if (dstCapacity < LZ4F_compressFrameBound(srcSize, &prefs))
+    if (dstCapacity < LZ4F_compressFrameBound(srcSize, &prefs))   /* condition to guarantee success */
         return err0r(LZ4F_ERROR_dstMaxSize_tooSmall);
 
     { size_t const headerSize = LZ4F_compressBegin(&cctxI, dstBuffer, dstCapacity, &prefs);  /* write header */
@@ -356,7 +356,7 @@ size_t LZ4F_compressFrame(void* dstBuffer, size_t dstCapacity, const void* srcBu
       if (LZ4F_isError(tailSize)) return tailSize;
       dstPtr += tailSize; }
 
-    if (prefs.compressionLevel >= LZ4HC_CLEVEL_MIN)   /* no allocation done with lz4 fast */
+    if (prefs.compressionLevel >= LZ4HC_CLEVEL_MIN)   /* Ctx allocation only for lz4hc */
         FREEMEM(cctxI.lz4CtxPtr);
 
     return (dstPtr - dstStart);
@@ -423,7 +423,7 @@ size_t LZ4F_compressBegin(LZ4F_cctx* cctxPtr, void* dstBuffer, size_t dstCapacit
     if (preferencesPtr == NULL) preferencesPtr = &prefNull;
     cctxPtr->prefs = *preferencesPtr;
 
-    /* ctx Management */
+    /* Ctx Management */
     {   U32 const tableID = (cctxPtr->prefs.compressionLevel < LZ4HC_CLEVEL_MIN) ? 1 : 2;  /* 0:nothing ; 1:LZ4 table ; 2:HC tables */
         if (cctxPtr->lz4CtxLevel < tableID) {
             FREEMEM(cctxPtr->lz4CtxPtr);
@@ -431,6 +431,7 @@ size_t LZ4F_compressBegin(LZ4F_cctx* cctxPtr, void* dstBuffer, size_t dstCapacit
                 cctxPtr->lz4CtxPtr = (void*)LZ4_createStream();
             else
                 cctxPtr->lz4CtxPtr = (void*)LZ4_createStreamHC();
+            if (cctxPtr->lz4CtxPtr == NULL) return err0r(LZ4F_ERROR_allocation_failed);
             cctxPtr->lz4CtxLevel = tableID;
         }
     }
@@ -444,10 +445,11 @@ size_t LZ4F_compressBegin(LZ4F_cctx* cctxPtr, void* dstBuffer, size_t dstCapacit
         requiredBuffSize = (cctxPtr->prefs.frameInfo.blockMode == LZ4F_blockLinked) * 64 KB;   /* just needs dict */
 
     if (cctxPtr->maxBufferSize < requiredBuffSize) {
-        cctxPtr->maxBufferSize = requiredBuffSize;
+        cctxPtr->maxBufferSize = 0;
         FREEMEM(cctxPtr->tmpBuff);
         cctxPtr->tmpBuff = (BYTE*)ALLOCATOR(requiredBuffSize);
         if (cctxPtr->tmpBuff == NULL) return err0r(LZ4F_ERROR_allocation_failed);
+        cctxPtr->maxBufferSize = requiredBuffSize;
     }
     cctxPtr->tmpIn = cctxPtr->tmpBuff;
     cctxPtr->tmpInSize = 0;
@@ -515,14 +517,14 @@ static size_t LZ4F_compressBlock(void* dst, const void* src, size_t srcSize, com
 
 static int LZ4F_localLZ4_compress_limitedOutput_withState(void* ctx, const char* src, char* dst, int srcSize, int dstCapacity, int level)
 {
-    (void) level;
-    return LZ4_compress_fast_extState(ctx, src, dst, srcSize, dstCapacity, 1);
+    int const acceleration = (level < -1) ? -level : 1;
+    return LZ4_compress_fast_extState(ctx, src, dst, srcSize, dstCapacity, acceleration);
 }
 
 static int LZ4F_localLZ4_compress_limitedOutput_continue(void* ctx, const char* src, char* dst, int srcSize, int dstCapacity, int level)
 {
-    (void) level;
-    return LZ4_compress_fast_continue((LZ4_stream_t*)ctx, src, dst, srcSize, dstCapacity, 1);
+    int const acceleration = (level < -1) ? -level : 1;
+    return LZ4_compress_fast_continue((LZ4_stream_t*)ctx, src, dst, srcSize, dstCapacity, acceleration);
 }
 
 static int LZ4F_localLZ4_compressHC_limitedOutput_continue(void* ctx, const char* src, char* dst, int srcSize, int dstSize, int level)
@@ -617,7 +619,7 @@ size_t LZ4F_compressUpdate(LZ4F_cctx* cctxPtr, void* dstBuffer, size_t dstCapaci
         if (compressOptionsPtr->stableSrc) {
             cctxPtr->tmpIn = cctxPtr->tmpBuff;
         } else {
-            int realDictSize = LZ4F_localSaveDict(cctxPtr);
+            int const realDictSize = LZ4F_localSaveDict(cctxPtr);
             if (realDictSize==0) return err0r(LZ4F_ERROR_GENERIC);
             cctxPtr->tmpIn = cctxPtr->tmpBuff + realDictSize;
         }
@@ -627,7 +629,7 @@ size_t LZ4F_compressUpdate(LZ4F_cctx* cctxPtr, void* dstBuffer, size_t dstCapaci
     if ((cctxPtr->tmpIn + blockSize) > (cctxPtr->tmpBuff + cctxPtr->maxBufferSize)   /* necessarily LZ4F_blockLinked && lastBlockCompressed==fromTmpBuffer */
         && !(cctxPtr->prefs.autoFlush))
     {
-        int realDictSize = LZ4F_localSaveDict(cctxPtr);
+        int const realDictSize = LZ4F_localSaveDict(cctxPtr);
         cctxPtr->tmpIn = cctxPtr->tmpBuff + realDictSize;
     }
 
diff --git a/lib/lz4frame.h b/lib/lz4frame.h
index 76b4e69..1b3e498 100644
--- a/lib/lz4frame.h
+++ b/lib/lz4frame.h
@@ -167,7 +167,7 @@ typedef struct {
  * All reserved fields must be set to zero. */
 typedef struct {
   LZ4F_frameInfo_t frameInfo;
-  int      compressionLevel;       /* 0 == default (fast mode); values above LZ4HC_CLEVEL_MAX count as LZ4HC_CLEVEL_MAX; values below 0 count as 0 */
+  int      compressionLevel;       /* 0 == default (fast mode); values above LZ4HC_CLEVEL_MAX count as LZ4HC_CLEVEL_MAX; values below 0 trigger "fast acceleration", proportional to value */
   unsigned autoFlush;              /* 1 == always flush (reduce usage of tmp buffer) */
   unsigned reserved[4];            /* must be zero for forward compatibility */
 } LZ4F_preferences_t;
diff --git a/tests/frametest.c b/tests/frametest.c
index ae8416b..a4c548e 100644
--- a/tests/frametest.c
+++ b/tests/frametest.c
@@ -218,6 +218,16 @@ int basicTests(U32 seed, double compressibility)
 
     /* test one-pass frame compression */
     testSize = COMPRESSIBLE_NOISE_LENGTH;
+
+    DISPLAYLEVEL(3, "LZ4F_compressFrame, using fast level -3 : ");
+    {   LZ4F_preferences_t fastCompressPrefs;
+        memset(&fastCompressPrefs, 0, sizeof(fastCompressPrefs));
+        fastCompressPrefs.compressionLevel = -3;
+        cSize = LZ4F_compressFrame(compressedBuffer, LZ4F_compressFrameBound(testSize, NULL), CNBuffer, testSize, &fastCompressPrefs);
+        if (LZ4F_isError(cSize)) goto _output_error;
+        DISPLAYLEVEL(3, "Compressed %u bytes into a %u bytes frame \n", (U32)testSize, (U32)cSize);
+    }
+
     DISPLAYLEVEL(3, "LZ4F_compressFrame, using default preferences : ");
     cSize = LZ4F_compressFrame(compressedBuffer, LZ4F_compressFrameBound(testSize, NULL), CNBuffer, testSize, NULL);
     if (LZ4F_isError(cSize)) goto _output_error;
@@ -618,7 +628,7 @@ int fuzzerTests(U32 seed, unsigned nbTests, unsigned startTest, double compressi
         prefs.frameInfo.contentChecksumFlag = (LZ4F_contentChecksum_t)(FUZ_rand(&randState) & 1);
         prefs.frameInfo.contentSize = ((FUZ_rand(&randState) & 0xF) == 1) ? srcSize : 0;
         prefs.autoFlush = neverFlush ? 0 : (FUZ_rand(&randState) & 7) == 2;
-        prefs.compressionLevel = FUZ_rand(&randState) % 5;
+        prefs.compressionLevel = -5 + (int)(FUZ_rand(&randState) % 11);
         if ((FUZ_rand(&randState) & 0xF) == 1) prefsPtr = NULL;
 
         DISPLAYUPDATE(2, "\r%5u   ", testNb);