allocation optimization for lz4frame compression

as noted by @yixiutt, the temporary buffer inside lz4frame compression
is being invalidated at end of compression,
forcing it to be re-allocated at next compression job.

This shouldn't be necessary.
This change was introduced in #236, as a way to fix #232,
but neither the issue is explained, nor why the patch fixes it.

This patch revert to previous behavior,
where temporary buffer is kept between compression calls.
This results in a net reduction of allocation workload.

Additionally, the temporary buffer should only need malloc(),
not calloc(), thus saving initialization.

This diff implements both changes.
Long fuzzer tests will be run to ensure that no sanitizer warning get triggered.

Additionally :
fixed a minor ubsan warning in LZ4F_decompress().

1 files changed, 6 insertions, 7 deletions

diff --git a/lib/lz4frame.c b/lib/lz4frame.c
index 174f9ae..b4caff4 100644
--- a/lib/lz4frame.c
+++ b/lib/lz4frame.c
@@ -264,7 +264,7 @@ typedef struct LZ4F_cctx_s
     LZ4F_CustomMem cmem;
     LZ4F_preferences_t prefs;
     U32    version;
-    U32    cStage;
+    U32    cStage;     /* 0 : compression uninitialized ; 1 : initialized, can compress */
     const LZ4F_CDict* cdict;
     size_t maxBlockSize;
     size_t maxBufferSize;
@@ -732,7 +732,7 @@ size_t LZ4F_compressBegin_usingCDict(LZ4F_cctx* cctxPtr,
         if (cctxPtr->maxBufferSize < requiredBuffSize) {
             cctxPtr->maxBufferSize = 0;
             LZ4F_free(cctxPtr->tmpBuff, cctxPtr->cmem);
-            cctxPtr->tmpBuff = (BYTE*)LZ4F_calloc(requiredBuffSize, cctxPtr->cmem);
+            cctxPtr->tmpBuff = (BYTE*)LZ4F_malloc(requiredBuffSize, cctxPtr->cmem);
             RETURN_ERROR_IF(cctxPtr->tmpBuff == NULL, allocation_failed);
             cctxPtr->maxBufferSize = requiredBuffSize;
     }   }
@@ -1176,7 +1176,6 @@ size_t LZ4F_compressEnd(LZ4F_cctx* cctxPtr,
     }
 
     cctxPtr->cStage = 0;   /* state is now re-usable (with identical preferences) */
-    cctxPtr->maxBufferSize = 0;  /* reuse HC context */
 
     if (cctxPtr->prefs.frameInfo.contentSize) {
         if (cctxPtr->prefs.frameInfo.contentSize != cctxPtr->totalInSize)
@@ -1722,10 +1721,10 @@ size_t LZ4F_decompress(LZ4F_dctx* dctx,
                     /* history management (linked blocks only)*/
                     if (dctx->frameInfo.blockMode == LZ4F_blockLinked) {
                         LZ4F_updateDict(dctx, dstPtr, sizeToCopy, dstStart, 0);
-                }   }
-
-                srcPtr += sizeToCopy;
-                dstPtr += sizeToCopy;
+                    }
+                    srcPtr += sizeToCopy;
+                    dstPtr += sizeToCopy;
+                }
                 if (sizeToCopy == dctx->tmpInTarget) {   /* all done */
                     if (dctx->frameInfo.blockChecksumFlag) {
                         dctx->tmpInSize = 0;