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slightly improved weight calculation

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translating into a tiny compression ratio improvement
This commit is contained in:
Yann Collet 2018-05-17 11:19:05 -07:00
parent 18fc3d3cd5
commit a243020d37
3 changed files with 16 additions and 14 deletions
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2
lib/compress/zstd_compress.c
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@ -1977,7 +1977,7 @@ static void ZSTD_storeLastLiterals(seqStore_t* seqStorePtr,
seqStorePtr->lit += lastLLSize;
}
static void ZSTD_resetSeqStore(seqStore_t* ssPtr)
void ZSTD_resetSeqStore(seqStore_t* ssPtr)
{
ssPtr->lit = ssPtr->litStart;
ssPtr->sequences = ssPtr->sequencesStart;

14
lib/compress/zstd_compress_internal.h
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@ -80,12 +80,12 @@ typedef enum { zop_dynamic=0, zop_predef } ZSTD_OptPrice_e;
typedef struct {
/* All tables are allocated inside cctx->workspace by ZSTD_resetCCtx_internal() */
U32* litFreq; /* table of literals statistics, of size 256 */
U32* litLengthFreq; /* table of litLength statistics, of size (MaxLL+1) */
U32* matchLengthFreq; /* table of matchLength statistics, of size (MaxML+1) */
U32* offCodeFreq; /* table of offCode statistics, of size (MaxOff+1) */
ZSTD_match_t* matchTable; /* list of found matches, of size ZSTD_OPT_NUM+1 */
ZSTD_optimal_t* priceTable; /* All positions tracked by optimal parser, of size ZSTD_OPT_NUM+1 */
U32* litFreq; /* table of literals statistics, of size 256 */
U32* litLengthFreq; /* table of litLength statistics, of size (MaxLL+1) */
U32* matchLengthFreq; /* table of matchLength statistics, of size (MaxML+1) */
U32* offCodeFreq; /* table of offCode statistics, of size (MaxOff+1) */
ZSTD_match_t* matchTable; /* list of found matches, of size ZSTD_OPT_NUM+1 */
ZSTD_optimal_t* priceTable; /* All positions tracked by optimal parser, of size ZSTD_OPT_NUM+1 */
U32 litSum; /* nb of literals */
U32 litLengthSum; /* nb of litLength codes */
@ -658,6 +658,8 @@ size_t ZSTD_initCStream_internal(ZSTD_CStream* zcs,
const ZSTD_CDict* cdict,
ZSTD_CCtx_params params, unsigned long long pledgedSrcSize);
void ZSTD_resetSeqStore(seqStore_t* ssPtr);
/*! ZSTD_compressStream_generic() :
* Private use only. To be called from zstdmt_compress.c in single-thread mode. */
size_t ZSTD_compressStream_generic(ZSTD_CStream* zcs,

14
lib/compress/zstd_opt.c
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@ -25,29 +25,29 @@
# define BITCOST_ACCURACY 0
# define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
# define WEIGHT(stat) ((void)opt, ZSTD_bitWeight(stat))
#elif 0 /* fractional bit accuracy */
#elif 1 /* fractional bit accuracy */
# define BITCOST_ACCURACY 8
# define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
# define WEIGHT(stat,opt) ((void)opt, ZSTD_fracWeight(stat))
#else /* opt==approx, ultra==accurate */
#else /* opt==approx, ultra==accurate */
# define BITCOST_ACCURACY 8
# define BITCOST_MULTIPLIER (1 << BITCOST_ACCURACY)
# define WEIGHT(stat,opt) (opt ? ZSTD_fracWeight(stat) : ZSTD_bitWeight(stat) )
# define WEIGHT(stat,opt) (opt ? ZSTD_fracWeight(stat) : ZSTD_bitWeight(stat))
#endif
MEM_STATIC U32 ZSTD_bitWeight(U32 stat)
{
return (ZSTD_highbit32((stat)+1) * BITCOST_MULTIPLIER);
return (ZSTD_highbit32(stat+1) * BITCOST_MULTIPLIER);
}
MEM_STATIC U32 ZSTD_fracWeight(U32 stat)
MEM_STATIC U32 ZSTD_fracWeight(U32 rawStat)
{
U32 const hb = stat ? ZSTD_highbit32(stat) : 0;
U32 const stat = rawStat + 1;
U32 const hb = ZSTD_highbit32(stat);
U32 const BWeight = hb * BITCOST_MULTIPLIER;
U32 const FWeight = (stat << BITCOST_ACCURACY) >> hb;
U32 const weight = BWeight + FWeight;
assert(hb + BITCOST_ACCURACY < 31);
DEBUGLOG(2, "stat=%u, hb=%u, weight=%u", stat, hb, weight)
return weight;
}