lz4frame : Added negative compression levels

3 files changed, 14 insertions, 14 deletions

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 fc0c7b5..356be8a 100644
--- a/lib/lz4frame.c
+++ b/lib/lz4frame.c
@@ -517,14 +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)
@@ -619,7 +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;
         }
@@ -629,7 +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;