minor optimization (DSpeed 665)

diff --git a/lib/bitstream.h b/lib/bitstream.h
index af9151adabf5d5873f5acc0df83b4be85625e90c..f2ed51bc5ab0a6c4ae8cc676ae6be3e19f6292da 100644 (file)
--- a/lib/bitstream.h
+++ b/lib/bitstream.h
@@ -285,6 +285,17 @@ MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, si
     return srcSize;
 }
 
+MEM_STATIC size_t BIT_getUpperBits(size_t bitD, U32 const start)
+{
+    return bitD >> start;
+}
+
+MEM_STATIC size_t BIT_getNBits(size_t bitD, U32 const nbBits, U32 const start)
+{
+    static const unsigned mask[] = { 0, 1, 3, 7, 0xF, 0x1F, 0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0x1FFFF, 0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF,  0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF };   /* up to 26 bits */
+    return (bitD >> start) & mask[nbBits];
+}
+
 MEM_STATIC size_t BIT_consumeFirstBits(size_t* bitDPtr, U32 const nbBits)
 {
     static const unsigned mask[] = { 0, 1, 3, 7, 0xF, 0x1F, 0x3F, 0x7F, 0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF, 0x1FFFF, 0x3FFFF, 0x7FFFF, 0xFFFFF, 0x1FFFFF, 0x3FFFFF, 0x7FFFFF,  0xFFFFFF, 0x1FFFFFF, 0x3FFFFFF };   /* up to 26 bits */

diff --git a/lib/zstd_decompress.c b/lib/zstd_decompress.c
index 1de3da1e03d177ccb93e350c8ce7b59c317655b1..3abd6bbc51f8dee0eff8fac3ac5553b4848733e0 100644 (file)
--- a/lib/zstd_decompress.c
+++ b/lib/zstd_decompress.c
@@ -635,7 +635,7 @@ static void ZSTD_decodeSequence(seq_t* seq, seqState_t* seqState, const U32 mls)
     U32 const mlBits = ML_bits[mlCode];
     U32 const ofBits = ofCode ? ofCode-1 : 0;
 
-    size_t allBits = BIT_readBits(&(seqState->DStream), llBits+mlBits+ofBits);
+    size_t const allBits = BIT_readBits(&(seqState->DStream), llBits+mlBits+ofBits);
 
     static const U32 LL_base[MaxLL+1] = {
                              0,  1,  2,  3,  4,  5,  6,  7,  8,  9,   10,    11,    12,    13,    14,     15,
@@ -655,9 +655,9 @@ static void ZSTD_decodeSequence(seq_t* seq, seqState_t* seqState, const U32 mls)
                 0x800000, 0x1000000, 0x2000000, 0x4000000, /*fake*/ 1, 1, 1, 1 };
 
     /* sequence */
-    seq->litLength = LL_base[llCode] + BIT_consumeFirstBits(&allBits, llBits);
-    seq->matchLength = ML_base[mlCode] + BIT_consumeFirstBits(&allBits, mlBits) + mls;
-    {   size_t const offset = ofCode ? OF_base[ofCode] + BIT_consumeFirstBits(&allBits, ofBits) :
+    seq->litLength = LL_base[llCode] + BIT_getNBits(allBits, llBits, 0);
+    seq->matchLength = ML_base[mlCode] + BIT_getNBits(allBits, mlBits, llBits) + mls;
+    {   size_t const offset = ofCode ? OF_base[ofCode] + BIT_getUpperBits(allBits, llBits+mlBits) :
                                        llCode ? seq->offset : seqState->prevOffset;
         if (ofCode | !llCode) seqState->prevOffset = seq->offset;   /* cmove */
         seq->offset = offset;