From: Yann Collet <yann.collet.73@gmail.com>
Date: Wed, 23 Mar 2016 12:57:49 +0000 (+0100)
Subject: improved decoding speed (660)
X-Git-Tag: v0.6.0^2~17^2~28^2~23
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=afab02098ac3c25ed7c689336dbd2b5d2faeaf97;p=thirdparty%2Fzstd.git

improved decoding speed (660)
---

diff --git a/lib/bitstream.h b/lib/bitstream.h
index d90c9b242..af9151ada 100644
--- a/lib/bitstream.h
+++ b/lib/bitstream.h
@@ -285,6 +285,14 @@ MEM_STATIC size_t BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, si
     return srcSize;
 }
 
+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 */
+    size_t const result = *bitDPtr & mask[nbBits];
+    *bitDPtr >>= nbBits;
+    return result;
+}
+
 /*! BIT_lookBits() :
  *  Provides next n bits from local register.
  *  local register is not modified (bits are still present for next read/look).
@@ -318,7 +326,7 @@ MEM_STATIC void BIT_skipBits(BIT_DStream_t* bitD, U32 nbBits)
  */
 MEM_STATIC size_t BIT_readBits(BIT_DStream_t* bitD, U32 nbBits)
 {
-    size_t value = BIT_lookBits(bitD, nbBits);
+    size_t const value = BIT_lookBits(bitD, nbBits);
     BIT_skipBits(bitD, nbBits);
     return value;
 }
@@ -327,7 +335,7 @@ MEM_STATIC size_t BIT_readBits(BIT_DStream_t* bitD, U32 nbBits)
 *   unsafe version; only works only if nbBits >= 1 */
 MEM_STATIC size_t BIT_readBitsFast(BIT_DStream_t* bitD, U32 nbBits)
 {
-    size_t value = BIT_lookBitsFast(bitD, nbBits);
+    size_t const value = BIT_lookBitsFast(bitD, nbBits);
     BIT_skipBits(bitD, nbBits);
     return value;
 }
diff --git a/lib/zstd_decompress.c b/lib/zstd_decompress.c
index a854aaf75..92af2b35d 100644
--- a/lib/zstd_decompress.c
+++ b/lib/zstd_decompress.c
@@ -652,16 +652,18 @@ static void ZSTD_decodeSequence(seq_t* seq, seqState_t* seqState, const U32 mls)
                 0x8000, 0x10000, 0x20000, 0x40000, 0x80000, 0x100000, 0x200000, 0x400000,
                 0x800000, 0x1000000, 0x2000000, 0x4000000, /*fake*/ 1, 1, 1, 1 };
 
-    seq->litLength = LL_base[llCode] + BIT_readBits(&(seqState->DStream), llBits);
-    seq->matchLength = ML_base[mlCode] + BIT_readBits(&(seqState->DStream), mlBits) + mls;
+    size_t allBits = BIT_readBits(&(seqState->DStream), llBits+mlBits+ofBits);
 
     /* Offset */
-    {   size_t const offset = ofCode ? OF_base[ofCode] + BIT_readBits(&(seqState->DStream), ofBits) :
+    {   size_t const offset = ofCode ? OF_base[ofCode] + BIT_consumeFirstBits(&allBits, ofBits) :
                                        llCode ? seq->offset : seqState->prevOffset;
         if (ofCode | !llCode) seqState->prevOffset = seq->offset;   /* cmove */
         seq->offset = offset;
     }
 
+    seq->matchLength = ML_base[mlCode] + BIT_consumeFirstBits(&allBits, mlBits) + mls;
+    seq->litLength = LL_base[llCode] + BIT_consumeFirstBits(&allBits, llBits);
+
     /* ANS state update */
     FSE_updateState(&(seqState->stateLL), &(seqState->DStream));
     FSE_updateState(&(seqState->stateML), &(seqState->DStream));