Introduce MIN and MAX bounds to LZ4_MEMORY_USAGE

ensure that `frametest` works fine with these values,
notably with low LZ4_MEMORY_USAGE (dict test notably)

following suggestions from @t-mat at #1016

4 files changed, 26 insertions, 15 deletions

diff --git a/lib/lz4.c b/lib/lz4.c
index 95bd349..a2272cf 100644
--- a/lib/lz4.c
+++ b/lib/lz4.c
@@ -867,7 +867,7 @@ LZ4_FORCE_INLINE int LZ4_compress_generic_validated(
                  const char* const source,
                  char* const dest,
                  const int inputSize,
-                 int *inputConsumed, /* only written when outputDirective == fillOutput */
+                 int*  inputConsumed, /* only written when outputDirective == fillOutput */
                  const int maxOutputSize,
                  const limitedOutput_directive outputDirective,
                  const tableType_t tableType,
diff --git a/lib/lz4.h b/lib/lz4.h
index a520adc..50f1d7a 100644
--- a/lib/lz4.h
+++ b/lib/lz4.h
@@ -118,15 +118,25 @@ LZ4LIB_API const char* LZ4_versionString (void);   /**< library version string;
 **************************************/
 /*!
  * LZ4_MEMORY_USAGE :
- * Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.)
- * Increasing memory usage improves compression ratio.
- * Reduced memory usage may improve speed, thanks to better cache locality.
+ * Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; )
+ * Increasing memory usage improves compression ratio, at the cost of speed.
+ * Reduced memory usage may improve speed at the cost of ratio, thanks to better cache locality.
  * Default value is 14, for 16KB, which nicely fits into Intel x86 L1 cache
  */
 #ifndef LZ4_MEMORY_USAGE
 # define LZ4_MEMORY_USAGE 14
 #endif
 
+#define LZ4_MEMORY_USAGE_MIN 10
+#define LZ4_MEMORY_USAGE_MAX 20
+
+#if (LZ4_MEMORY_USAGE < LZ4_MEMORY_USAGE_MIN)
+#  error "LZ4_MEMORY_USAGE is too small !"
+#endif
+
+#if (LZ4_MEMORY_USAGE > LZ4_MEMORY_USAGE_MAX)
+#  error "LZ4_MEMORY_USAGE is too large !"
+#endif
 
 /*-************************************
 *  Simple Functions
diff --git a/lib/lz4frame.c b/lib/lz4frame.c
index 73f21fc..f4ea02a 100644
--- a/lib/lz4frame.c
+++ b/lib/lz4frame.c
@@ -485,12 +485,12 @@ struct LZ4F_CDict_s {
  *  When compressing multiple messages / blocks with the same dictionary, it's recommended to load it just once.
  *  LZ4F_createCDict() will create a digested dictionary, ready to start future compression operations without startup delay.
  *  LZ4F_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only.
- * `dictBuffer` can be released after LZ4F_CDict creation, since its content is copied within CDict
+ * @dictBuffer can be released after LZ4F_CDict creation, since its content is copied within CDict
  * @return : digested dictionary for compression, or NULL if failed */
 LZ4F_CDict* LZ4F_createCDict(const void* dictBuffer, size_t dictSize)
 {
     const char* dictStart = (const char*)dictBuffer;
-    LZ4F_CDict* cdict = (LZ4F_CDict*) ALLOC(sizeof(*cdict));
+    LZ4F_CDict* const cdict = (LZ4F_CDict*) ALLOC(sizeof(*cdict));
     DEBUGLOG(4, "LZ4F_createCDict");
     if (!cdict) return NULL;
     if (dictSize > 64 KB) {
diff --git a/tests/frametest.c b/tests/frametest.c
index e0fff0e..09def51 100644
--- a/tests/frametest.c
+++ b/tests/frametest.c
@@ -535,8 +535,9 @@ int basicTests(U32 seed, double compressibility)
     }
 
     /* Dictionary compression test */
-    {   size_t const dictSize = 63 KB;
-        size_t const dstCapacity = LZ4F_compressFrameBound(dictSize, NULL);
+    {   size_t const dictSize = 7 KB; /* small enough for LZ4_MEMORY_USAGE == 10 */
+        size_t const srcSize = 65 KB; /* must be > 64 KB to avoid short-size optimizations */
+        size_t const dstCapacity = LZ4F_compressFrameBound(srcSize, NULL);
         size_t cSizeNoDict, cSizeWithDict;
         LZ4F_CDict* const cdict = LZ4F_createCDict(CNBuffer, dictSize);
         if (cdict == NULL) goto _output_error;
@@ -545,7 +546,7 @@ int basicTests(U32 seed, double compressibility)
         DISPLAYLEVEL(3, "LZ4F_compressFrame_usingCDict, with NULL dict : ");
         CHECK_V(cSizeNoDict,
                 LZ4F_compressFrame_usingCDict(cctx, compressedBuffer, dstCapacity,
-                                              CNBuffer, dictSize,
+                                              CNBuffer, srcSize,
                                               NULL, NULL) );
         DISPLAYLEVEL(3, "%u bytes \n", (unsigned)cSizeNoDict);
 
@@ -554,19 +555,19 @@ int basicTests(U32 seed, double compressibility)
         DISPLAYLEVEL(3, "LZ4F_compressFrame_usingCDict, with dict : ");
         CHECK_V(cSizeWithDict,
                 LZ4F_compressFrame_usingCDict(cctx, compressedBuffer, dstCapacity,
-                                              CNBuffer, dictSize,
+                                              CNBuffer, srcSize,
                                               cdict, NULL) );
         DISPLAYLEVEL(3, "compressed %u bytes into %u bytes \n",
-                        (unsigned)dictSize, (unsigned)cSizeWithDict);
-        if ((LZ4_DISTANCE_MAX > dictSize) && (cSizeWithDict >= cSizeNoDict)) {
+                        (unsigned)srcSize, (unsigned)cSizeWithDict);
+        if (cSizeWithDict > cSizeNoDict) {
             DISPLAYLEVEL(3, "cSizeWithDict (%zu) should have been more compact than cSizeNoDict(%zu) \n", cSizeWithDict, cSizeNoDict);
             goto _output_error;  /* must be more efficient */
         }
-        crcOrig = XXH64(CNBuffer, dictSize, 0);
+        crcOrig = XXH64(CNBuffer, srcSize, 0);
 
         DISPLAYLEVEL(3, "LZ4F_decompress_usingDict : ");
         {   LZ4F_dctx* dctx;
-            size_t decodedSize = COMPRESSIBLE_NOISE_LENGTH;
+            size_t decodedSize = srcSize;
             size_t compressedSize = cSizeWithDict;
             CHECK( LZ4F_createDecompressionContext(&dctx, LZ4F_VERSION) );
             CHECK( LZ4F_decompress_usingDict(dctx,
@@ -575,7 +576,7 @@ int basicTests(U32 seed, double compressibility)
                                         CNBuffer, dictSize,
                                         NULL) );
             if (compressedSize != cSizeWithDict) goto _output_error;
-            if (decodedSize != dictSize) goto _output_error;
+            if (decodedSize != srcSize) goto _output_error;
             { U64 const crcDest = XXH64(decodedBuffer, decodedSize, 0);
               if (crcDest != crcOrig) goto _output_error; }
             DISPLAYLEVEL(3, "Regenerated %u bytes \n", (U32)decodedSize);