small decompression speed boost for very small data

lib/common/zstd_internal.h

@@ -108,7 +108,8 @@ static const U32 LL_bits[MaxLL+1] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 static const S16 LL_defaultNorm[MaxLL+1] = { 4, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1,
                                              2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 1, 1, 1, 1, 1,
                                             -1,-1,-1,-1 };
-static const U32 LL_defaultNormLog = 6;
+#define LL_DEFAULTNORMLOG 6  /* for static allocation */
+static const U32 LL_defaultNormLog = LL_DEFAULTNORMLOG;
 
 static const U32 ML_bits[MaxML+1] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                                       0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
@@ -118,11 +119,13 @@ static const S16 ML_defaultNorm[MaxML+1] = { 1, 4, 3, 2, 2, 2, 2, 2, 2, 1, 1, 1,
                                              1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
                                              1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,-1,-1,
                                             -1,-1,-1,-1,-1 };
-static const U32 ML_defaultNormLog = 6;
+#define ML_DEFAULTNORMLOG 6  /* for static allocation */
+static const U32 ML_defaultNormLog = ML_DEFAULTNORMLOG;
 
 static const S16 OF_defaultNorm[MaxOff+1] = { 1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1,
                                               1, 1, 1, 1, 1, 1, 1, 1,-1,-1,-1,-1,-1 };
-static const U32 OF_defaultNormLog = 5;
+#define OF_DEFAULTNORMLOG 5  /* for static allocation */
+static const U32 OF_defaultNormLog = OF_DEFAULTNORMLOG;
 
 
 /*-*******************************************

lib/decompress/zstd_decompress.c

@@ -482,23 +482,203 @@ size_t ZSTD_decodeLiteralsBlock(ZSTD_DCtx* dctx,
 }
 
 
+typedef union {
+    FSE_decode_t realData;
+    U32 alignedBy4;
+} FSE_decode_t4;
+
+static const FSE_decode_t4 LL_defaultDTable[(1<<LL_DEFAULTNORMLOG)+1] = {
+    { { LL_DEFAULTNORMLOG, 1, 1 } }, /* header : tableLog, fastMode, fastMode */
+    { {  0,  0,  4 } },              /* 0 : base, symbol, bits */
+    { { 16,  0,  4 } },
+    { { 32,  1,  5 } },
+    { {  0,  3,  5 } },
+    { {  0,  4,  5 } },
+    { {  0,  6,  5 } },
+    { {  0,  7,  5 } },
+    { {  0,  9,  5 } },
+    { {  0, 10,  5 } },
+    { {  0, 12,  5 } },
+    { {  0, 14,  6 } },
+    { {  0, 16,  5 } },
+    { {  0, 18,  5 } },
+    { {  0, 19,  5 } },
+    { {  0, 21,  5 } },
+    { {  0, 22,  5 } },
+    { {  0, 24,  5 } },
+    { { 32, 25,  5 } },
+    { {  0, 26,  5 } },
+    { {  0, 27,  6 } },
+    { {  0, 29,  6 } },
+    { {  0, 31,  6 } },
+    { { 32,  0,  4 } },
+    { {  0,  1,  4 } },
+    { {  0,  2,  5 } },
+    { { 32,  4,  5 } },
+    { {  0,  5,  5 } },
+    { { 32,  7,  5 } },
+    { {  0,  8,  5 } },
+    { { 32, 10,  5 } },
+    { {  0, 11,  5 } },
+    { {  0, 13,  6 } },
+    { { 32, 16,  5 } },
+    { {  0, 17,  5 } },
+    { { 32, 19,  5 } },
+    { {  0, 20,  5 } },
+    { { 32, 22,  5 } },
+    { {  0, 23,  5 } },
+    { {  0, 25,  4 } },
+    { { 16, 25,  4 } },
+    { { 32, 26,  5 } },
+    { {  0, 28,  6 } },
+    { {  0, 30,  6 } },
+    { { 48,  0,  4 } },
+    { { 16,  1,  4 } },
+    { { 32,  2,  5 } },
+    { { 32,  3,  5 } },
+    { { 32,  5,  5 } },
+    { { 32,  6,  5 } },
+    { { 32,  8,  5 } },
+    { { 32,  9,  5 } },
+    { { 32, 11,  5 } },
+    { { 32, 12,  5 } },
+    { {  0, 15,  6 } },
+    { { 32, 17,  5 } },
+    { { 32, 18,  5 } },
+    { { 32, 20,  5 } },
+    { { 32, 21,  5 } },
+    { { 32, 23,  5 } },
+    { { 32, 24,  5 } },
+    { {  0, 35,  6 } },
+    { {  0, 34,  6 } },
+    { {  0, 33,  6 } },
+    { {  0, 32,  6 } },
+};   /* LL_defaultDTable */
+
+static const FSE_decode_t4 ML_defaultDTable[(1<<ML_DEFAULTNORMLOG)+1] = {
+    { { ML_DEFAULTNORMLOG, 1, 1 } }, /* header : tableLog, fastMode, fastMode */
+    { {  0,  0,  6 } },              /* 0 : base, symbol, bits */
+    { {  0,  1,  4 } },
+    { { 32,  2,  5 } },
+    { {  0,  3,  5 } },
+    { {  0,  5,  5 } },
+    { {  0,  6,  5 } },
+    { {  0,  8,  5 } },
+    { {  0, 10,  6 } },
+    { {  0, 13,  6 } },
+    { {  0, 16,  6 } },
+    { {  0, 19,  6 } },
+    { {  0, 22,  6 } },
+    { {  0, 25,  6 } },
+    { {  0, 28,  6 } },
+    { {  0, 31,  6 } },
+    { {  0, 33,  6 } },
+    { {  0, 35,  6 } },
+    { {  0, 37,  6 } },
+    { {  0, 39,  6 } },
+    { {  0, 41,  6 } },
+    { {  0, 43,  6 } },
+    { {  0, 45,  6 } },
+    { { 16,  1,  4 } },
+    { {  0,  2,  4 } },
+    { { 32,  3,  5 } },
+    { {  0,  4,  5 } },
+    { { 32,  6,  5 } },
+    { {  0,  7,  5 } },
+    { {  0,  9,  6 } },
+    { {  0, 12,  6 } },
+    { {  0, 15,  6 } },
+    { {  0, 18,  6 } },
+    { {  0, 21,  6 } },
+    { {  0, 24,  6 } },
+    { {  0, 27,  6 } },
+    { {  0, 30,  6 } },
+    { {  0, 32,  6 } },
+    { {  0, 34,  6 } },
+    { {  0, 36,  6 } },
+    { {  0, 38,  6 } },
+    { {  0, 40,  6 } },
+    { {  0, 42,  6 } },
+    { {  0, 44,  6 } },
+    { { 32,  1,  4 } },
+    { { 48,  1,  4 } },
+    { { 16,  2,  4 } },
+    { { 32,  4,  5 } },
+    { { 32,  5,  5 } },
+    { { 32,  7,  5 } },
+    { { 32,  8,  5 } },
+    { {  0, 11,  6 } },
+    { {  0, 14,  6 } },
+    { {  0, 17,  6 } },
+    { {  0, 20,  6 } },
+    { {  0, 23,  6 } },
+    { {  0, 26,  6 } },
+    { {  0, 29,  6 } },
+    { {  0, 52,  6 } },
+    { {  0, 51,  6 } },
+    { {  0, 50,  6 } },
+    { {  0, 49,  6 } },
+    { {  0, 48,  6 } },
+    { {  0, 47,  6 } },
+    { {  0, 46,  6 } },
+};   /* ML_defaultDTable */
+
+static const FSE_decode_t4 OF_defaultDTable[(1<<OF_DEFAULTNORMLOG)+1] = {
+    { { OF_DEFAULTNORMLOG, 1, 1 } }, /* header : tableLog, fastMode, fastMode */
+    { {  0,  0,  5 } },              /* 0 : base, symbol, bits */
+    { {  0,  6,  4 } },
+    { {  0,  9,  5 } },
+    { {  0, 15,  5 } },
+    { {  0, 21,  5 } },
+    { {  0,  3,  5 } },
+    { {  0,  7,  4 } },
+    { {  0, 12,  5 } },
+    { {  0, 18,  5 } },
+    { {  0, 23,  5 } },
+    { {  0,  5,  5 } },
+    { {  0,  8,  4 } },
+    { {  0, 14,  5 } },
+    { {  0, 20,  5 } },
+    { {  0,  2,  5 } },
+    { { 16,  7,  4 } },
+    { {  0, 11,  5 } },
+    { {  0, 17,  5 } },
+    { {  0, 22,  5 } },
+    { {  0,  4,  5 } },
+    { { 16,  8,  4 } },
+    { {  0, 13,  5 } },
+    { {  0, 19,  5 } },
+    { {  0,  1,  5 } },
+    { { 16,  6,  4 } },
+    { {  0, 10,  5 } },
+    { {  0, 16,  5 } },
+    { {  0, 28,  5 } },
+    { {  0, 27,  5 } },
+    { {  0, 26,  5 } },
+    { {  0, 25,  5 } },
+    { {  0, 24,  5 } },
+};   /* OF_defaultDTable */
+
 /*! ZSTD_buildSeqTable() :
     @return : nb bytes read from src,
               or an error code if it fails, testable with ZSTD_isError()
 */
-static size_t ZSTD_buildSeqTable(FSE_DTable* DTable, symbolEncodingType_e type, U32 max, U32 maxLog,
+static size_t ZSTD_buildSeqTable(FSE_DTable* DTableSpace, const FSE_DTable** DTablePtr,
+                                 symbolEncodingType_e type, U32 max, U32 maxLog,
                                  const void* src, size_t srcSize,
-                                 const S16* defaultNorm, U32 defaultLog, U32 flagRepeatTable)
+                                 const FSE_decode_t4* defaultTable, U32 flagRepeatTable)
 {
+    const void* const tmpPtr = defaultTable;   /* bypass strict aliasing */
     switch(type)
     {
     case set_rle :
         if (!srcSize) return ERROR(srcSize_wrong);
         if ( (*(const BYTE*)src) > max) return ERROR(corruption_detected);
-        FSE_buildDTable_rle(DTable, *(const BYTE*)src);   /* if *src > max, data is corrupted */
+        FSE_buildDTable_rle(DTableSpace, *(const BYTE*)src);
+        *DTablePtr = DTableSpace;
         return 1;
     case set_basic :
-        FSE_buildDTable(DTable, defaultNorm, max, defaultLog);
+        *DTablePtr = (const FSE_DTable*)tmpPtr;
         return 0;
     case set_repeat:
         if (!flagRepeatTable) return ERROR(corruption_detected);
@@ -510,12 +690,12 @@ static size_t ZSTD_buildSeqTable(FSE_DTable* DTable, symbolEncodingType_e type,
             size_t const headerSize = FSE_readNCount(norm, &max, &tableLog, src, srcSize);
             if (FSE_isError(headerSize)) return ERROR(corruption_detected);
             if (tableLog > maxLog) return ERROR(corruption_detected);
-            FSE_buildDTable(DTable, norm, max, tableLog);
+            FSE_buildDTable(DTableSpace, norm, max, tableLog);
+            *DTablePtr = DTableSpace;
             return headerSize;
     }   }
 }
 
-
 size_t ZSTD_decodeSeqHeaders(ZSTD_DCtx* dctx, int* nbSeqPtr,
                              const void* src, size_t srcSize)
 {
@@ -546,21 +726,25 @@ size_t ZSTD_decodeSeqHeaders(ZSTD_DCtx* dctx, int* nbSeqPtr,
         ip++;
 
         /* Build DTables */
-        {   size_t const llhSize = ZSTD_buildSeqTable(dctx->LLTable, LLtype, MaxLL, LLFSELog, ip, iend-ip, LL_defaultNorm, LL_defaultNormLog, dctx->fseEntropy);
+        {   size_t const llhSize = ZSTD_buildSeqTable(dctx->LLTable, &dctx->LLTptr,
+                                                      LLtype, MaxLL, LLFSELog,
+                                                      ip, iend-ip, LL_defaultDTable, dctx->fseEntropy);
             if (ZSTD_isError(llhSize)) return ERROR(corruption_detected);
-            if (LLtype != set_repeat) dctx->LLTptr = dctx->LLTable;
             ip += llhSize;
         }
-        {   size_t const ofhSize = ZSTD_buildSeqTable(dctx->OFTable, OFtype, MaxOff, OffFSELog, ip, iend-ip, OF_defaultNorm, OF_defaultNormLog, dctx->fseEntropy);
+        {   size_t const ofhSize = ZSTD_buildSeqTable(dctx->OFTable, &dctx->OFTptr,
+                                                      OFtype, MaxOff, OffFSELog,
+                                                      ip, iend-ip, OF_defaultDTable, dctx->fseEntropy);
             if (ZSTD_isError(ofhSize)) return ERROR(corruption_detected);
-            if (OFtype != set_repeat) dctx->OFTptr = dctx->OFTable;
             ip += ofhSize;
         }
-        {   size_t const mlhSize = ZSTD_buildSeqTable(dctx->MLTable, MLtype, MaxML, MLFSELog, ip, iend-ip, ML_defaultNorm, ML_defaultNormLog, dctx->fseEntropy);
+        {   size_t const mlhSize = ZSTD_buildSeqTable(dctx->MLTable, &dctx->MLTptr,
+                                                      MLtype, MaxML, MLFSELog,
+                                                      ip, iend-ip, ML_defaultDTable, dctx->fseEntropy);
             if (ZSTD_isError(mlhSize)) return ERROR(corruption_detected);
-            if (MLtype != set_repeat) dctx->MLTptr = dctx->MLTable;
             ip += mlhSize;
-    }   }
+        }
+    }
 
     return ip-istart;
 }