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zstd_opt: minor speed optimization

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Calculate reference log2sums only once per serie of sequence
(as opposed to once per sequence)

Also: improved code comments
This commit is contained in:
Yann Collet 2017-11-18 16:24:02 -08:00
parent daebc7fe26
commit e717a5b0dd
2 changed files with 24 additions and 23 deletions
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19
lib/compress/zstd_compress_internal.h
View File

@ -72,26 +72,27 @@ typedef struct {
} ZSTD_optimal_t;
typedef struct {
U32* litFreq;
U32* litLengthFreq;
U32* matchLengthFreq;
U32* offCodeFreq;
ZSTD_match_t* matchTable;
ZSTD_optimal_t* priceTable;
/* 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 litSum; /* nb of literals */
U32 litLengthSum; /* nb of litLength codes */
U32 matchLengthSum; /* nb of matchLength codes */
U32 matchSum; /* one argument to calculate `factor` */
U32 matchSum; /* a strange argument used in calculating `factor` */
U32 offCodeSum; /* nb of offset codes */
/* begin updated by ZSTD_setLog2Prices */
U32 log2litSum; /* pow2 to compare log2(litfreq) to */
U32 log2litLengthSum; /* pow2 to compare log2(llfreq) to */
U32 log2matchLengthSum; /* pow2 to compare log2(mlfreq) to */
U32 log2offCodeSum; /* pow2 to compare log2(offreq) to */
U32 factor; /* added to calculate ZSTD_getPrice() (but why?) */
U32 factor; /* fixed cost added when calculating ZSTD_getPrice() (but why ? seems to favor less sequences) */
/* end : updated by ZSTD_setLog2Prices */
U32 staticPrices; /* prices follow a static cost structure, statistics are irrelevant */
U32 staticPrices; /* prices follow a pre-defined cost structure, statistics are irrelevant */
U32 cachedPrice;
U32 cachedLitLength;
const BYTE* cachedLiterals;

28
lib/compress/zstd_opt.c
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@ -13,7 +13,7 @@
#include "zstd_lazy.h" /* ZSTD_updateTree, ZSTD_updateTree_extDict */
#define ZSTD_LITFREQ_ADD 2 /* sort of scaling factor for litSum and litFreq (why the need ?), but also used for matchSum ? */
#define ZSTD_LITFREQ_ADD 2 /* scaling factor for litFreq, so that frequencies adapt faster to new stats. Also used for matchSum (?) */
#define ZSTD_FREQ_DIV 4 /* log factor when using previous stats to init next stats */
#define ZSTD_MAX_PRICE (1<<30)
@ -161,25 +161,26 @@ FORCE_INLINE_TEMPLATE U32 ZSTD_getPrice(optState_t* optPtr, U32 litLength, const
}
static void ZSTD_updatePrice(optState_t* optPtr, U32 litLength, const BYTE* literals, U32 offset, U32 matchLength)
static void ZSTD_updateStats(optState_t* optPtr, U32 litLength, const BYTE* literals, U32 offsetCode, U32 matchLength)
{
U32 u;
/* literals */
optPtr->litSum += litLength*ZSTD_LITFREQ_ADD;
for (u=0; u < litLength; u++)
optPtr->litFreq[literals[u]] += ZSTD_LITFREQ_ADD;
{ U32 u;
optPtr->litSum += litLength*ZSTD_LITFREQ_ADD;
for (u=0; u < litLength; u++)
optPtr->litFreq[literals[u]] += ZSTD_LITFREQ_ADD;
}
/* literal Length */
{ const U32 llCode = ZSTD_LLcode(litLength);
{ U32 const llCode = ZSTD_LLcode(litLength);
optPtr->litLengthFreq[llCode]++;
optPtr->litLengthSum++;
}
/* match offset */
{ BYTE const offCode = (BYTE)ZSTD_highbit32(offset+1);
optPtr->offCodeSum++;
/* match offset code (0-2=>repCode; 3+=>offset+2) */
{ U32 const offCode = ZSTD_highbit32(offsetCode+1);
assert(offCode <= MaxOff);
optPtr->offCodeFreq[offCode]++;
optPtr->offCodeSum++;
}
/* match Length */
@ -188,8 +189,6 @@ static void ZSTD_updatePrice(optState_t* optPtr, U32 litLength, const BYTE* lite
optPtr->matchLengthFreq[mlCode]++;
optPtr->matchLengthSum++;
}
ZSTD_setLog2Prices(optPtr);
}
@ -646,10 +645,11 @@ _shortestPath: /* cur, last_pos, best_mlen, best_off have to be set */
}
}
ZSTD_updatePrice(optStatePtr, llen, anchor, offset, mlen);
ZSTD_updateStats(optStatePtr, llen, anchor, offset, mlen);
ZSTD_storeSeq(seqStorePtr, llen, anchor, offset, mlen-MINMATCH);
anchor = ip;
} }
ZSTD_setLog2Prices(optStatePtr);
} /* for (cur=0; cur < last_pos; ) */
/* Save reps for next block */