small extDict : fixed side-effect

don't fix dictionaries of size 0.
setting dictEnd == source triggers prefix mode,
thus removing possibility to use CDict.

3 files changed, 8 insertions, 3 deletions

diff --git a/lib/lz4.c b/lib/lz4.c
index 9a922b5..e51a3e0 100644
--- a/lib/lz4.c
+++ b/lib/lz4.c
@@ -683,13 +683,12 @@ LZ4_FORCE_INLINE int LZ4_compress_generic(
     /* Init conditions */
     if (outputLimited == fillOutput && maxOutputSize < 1) return 0; /* Impossible to store anything */
     if ((U32)inputSize > (U32)LZ4_MAX_INPUT_SIZE) return 0;   /* Unsupported inputSize, too large (or negative) */
+    if ((tableType == byU16) && (inputSize>=LZ4_64Klimit)) return 0;  /* Size too large (not within 64K limit) */
     if (tableType==byPtr) assert(dictDirective==noDict);      /* only supported use case with byPtr */
     assert(acceleration >= 1);
 
     lowLimit = (const BYTE*)source - (dictDirective == withPrefix64k ? dictSize : 0);
 
-    if ((tableType == byU16) && (inputSize>=LZ4_64Klimit)) return 0;  /* Size too large (not within 64K limit) */
-
     /* Update context state */
     if (dictDirective == usingDictCtx) {
         /* Subsequent linked blocks can't use the dictionary. */
@@ -1259,12 +1258,16 @@ int LZ4_compress_fast_continue (LZ4_stream_t* LZ4_stream, const char* source, ch
     LZ4_stream_t_internal* streamPtr = &LZ4_stream->internal_donotuse;
     const BYTE* dictEnd = streamPtr->dictionary + streamPtr->dictSize;
 
+    DEBUGLOG(5, "LZ4_compress_fast_continue (inputSize=%i)", inputSize);
+
     if (streamPtr->initCheck) return 0;   /* Uninitialized structure detected */
     LZ4_renormDictT(streamPtr, inputSize);   /* avoid index overflow */
     if (acceleration < 1) acceleration = ACCELERATION_DEFAULT;
 
     /* invalidate tiny dictionaries */
-    if (streamPtr->dictSize < 4) {
+    if ( (streamPtr->dictSize-1 < 4)   /* intentional underflow */
+      && (dictEnd != (const BYTE*)source) ) {
+        DEBUGLOG(5, "LZ4_compress_fast_continue: dictSize(%u) at addr:%p is too small", streamPtr->dictSize, streamPtr->dictionary);
         streamPtr->dictSize = 0;
         streamPtr->dictionary = (const BYTE*)source;
         dictEnd = (const BYTE*)source;
diff --git a/lib/lz4frame.c b/lib/lz4frame.c
index 4e40816..e1d0b1d 100644
--- a/lib/lz4frame.c
+++ b/lib/lz4frame.c
@@ -472,6 +472,7 @@ LZ4F_CDict* LZ4F_createCDict(const void* dictBuffer, size_t dictSize)
 {
     const char* dictStart = (const char*)dictBuffer;
     LZ4F_CDict* cdict = (LZ4F_CDict*) ALLOC(sizeof(*cdict));
+    DEBUGLOG(4, "LZ4F_createCDict");
     if (!cdict) return NULL;
     if (dictSize > 64 KB) {
         dictStart += dictSize - 64 KB;
diff --git a/tests/frametest.c b/tests/frametest.c
index 21d883d..4efeb6f 100644
--- a/tests/frametest.c
+++ b/tests/frametest.c
@@ -520,6 +520,7 @@ int basicTests(U32 seed, double compressibility)
         LZ4F_CDict* const cdict = LZ4F_createCDict(CNBuffer, dictSize);
         if (cdict == NULL) goto _output_error;
         CHECK( LZ4F_createCompressionContext(&cctx, LZ4F_VERSION) );
+        
         DISPLAYLEVEL(3, "LZ4F_compressFrame_usingCDict, with NULL dict : ");
         CHECK_V(cSizeNoDict,
                 LZ4F_compressFrame_usingCDict(cctx, compressedBuffer, dstCapacity,