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improved decoding speed (660)

dev
Yann Collet 2016-03-23 13:57:49 +01:00
parent fd69225086
commit afab02098a
2 changed files with 15 additions and 5 deletions
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12
lib/bitstream.h
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@ -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;
}

8
lib/zstd_decompress.c
View File

@ -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));