experiments with ZSTD_decodeSequence

lib/zstd_decompress.c

@@ -687,14 +687,29 @@ static void ZSTD_decodeSequence(seq_t* seq, seqState_t* seqState, const U32 mls)
 
 
     {   size_t offset;
-        if (ofCode) {
+#if 0
-            offset = OF_base[ofCode] + BIT_readBits(&(seqState->DStream), ofBits);   /* <=  26 bits */
+        if (!ofCode) {
-            if (MEM_32bits()) BIT_reloadDStream(&(seqState->DStream));
+            if (!llCode) {
+                offset = seqState->prevOffset[1];
+                seqState->prevOffset[1] = seqState->prevOffset[0];
+                seqState->prevOffset[0] = offset;
 
             } else {
+                offset = seqState->prevOffset[0];
+            }
+        } else {
+            offset = OF_base[ofCode] + BIT_readBits(&(seqState->DStream), ofBits);   /* <=  26 bits */
+            if (MEM_32bits()) BIT_reloadDStream(&(seqState->DStream));
+#else
+        if (!ofCode)
             offset = 0;
+        else {
+            offset = OF_base[ofCode] + BIT_readBits(&(seqState->DStream), ofBits);   /* <=  26 bits */
+            if (MEM_32bits()) BIT_reloadDStream(&(seqState->DStream));
         }
         
+        {
+#endif
             if (offset < ZSTD_REP_NUM) {
                 if (llCode == 0 && offset <= 1) offset = 1-offset;
 
@@ -710,7 +725,6 @@ static void ZSTD_decodeSequence(seq_t* seq, seqState_t* seqState, const U32 mls)
                 } else {
                     offset = seqState->prevOffset[0];
                 }
-
             } else {
                 offset -= ZSTD_REP_MOVE;
     #if 1 // faster without kSlotNew
@@ -725,7 +739,7 @@ static void ZSTD_decodeSequence(seq_t* seq, seqState_t* seqState, const U32 mls)
                 seqState->prevOffset[kSlotNew] = offset;
     #endif
             }
-        
+        }
         seq->offset = offset;
     }
     

lib/zstd_internal.h

@@ -46,6 +46,17 @@
 #define MIN(a,b) ((a)<(b) ? (a) : (b))
 #define MAX(a,b) ((a)>(b) ? (a) : (b))
 
+#define ZSTD_GCC_VERSION (__GNUC__ * 100 + __GNUC_MINOR__)
+
+#if (ZSTD_GCC_VERSION >= 302) || (__INTEL_COMPILER >= 800) || defined(__clang__)
+#  define expect(expr,value)    (__builtin_expect ((expr),(value)) )
+#else
+#  define expect(expr,value)    (expr)
+#endif
+
+#define likely(expr)     expect((expr) != 0, 1)
+#define unlikely(expr)   expect((expr) != 0, 0)
+
 
 /*-*************************************
 *  Common constants