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Code Issues Releases 1 Activity

slightly improved ratio at -22

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merging of repcode search into btsearch introduced a small compression ratio regressio at max level :
1.3.2 : 52728769
after repMerge patch : 52760789 (+32020)

A few minor changes have produced this difference.
They can be hard to spot.

This patch buys back about half of the difference,
by no longer inserting position at hc3 when a long match is found there.
It feels strangely counter-intuitive, but works :
after this patch : 52742555 (-18234)
This commit is contained in:
Yann Collet
2017-11-19 13:39:12 -08:00
parent 99435dbbab
commit 42c1e64270
3 changed files with 16 additions and 13 deletions
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15
lib/compress/zstd_lazy.c
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@ -16,8 +16,8 @@
* Binary Tree search
***************************************/
/** ZSTD_insertBt1() : add one or multiple positions to tree.
* ip : assumed <= iend-8 .
* @return : nb of positions added */
* ip : assumed <= iend-8 .
* @return : nb of positions added */
static U32 ZSTD_insertBt1(ZSTD_CCtx* zc,
const BYTE* const ip, const BYTE* const iend,
U32 nbCompares, U32 const mls, U32 const extDict)
@ -42,7 +42,7 @@ static U32 ZSTD_insertBt1(ZSTD_CCtx* zc,
U32* largerPtr = smallerPtr + 1;
U32 dummy32; /* to be nullified at the end */
U32 const windowLow = zc->lowLimit;
U32 matchEndIdx = current+8;
U32 matchEndIdx = current+8+1;
size_t bestLength = 8;
#ifdef ZSTD_C_PREDICT
U32 predictedSmall = *(bt + 2*((current-1)&btMask) + 0);
@ -122,8 +122,8 @@ static U32 ZSTD_insertBt1(ZSTD_CCtx* zc,
*smallerPtr = *largerPtr = 0;
if (bestLength > 384) return MIN(192, (U32)(bestLength - 384)); /* speed optimization */
if (matchEndIdx > current + 8) return matchEndIdx - (current + 8);
return 1;
assert(matchEndIdx > current + 8);
return matchEndIdx - (current + 8);
}
FORCE_INLINE_TEMPLATE
@ -182,7 +182,7 @@ static size_t ZSTD_insertBtAndFindBestMatch (
const U32 windowLow = zc->lowLimit;
U32* smallerPtr = bt + 2*(current&btMask);
U32* largerPtr = bt + 2*(current&btMask) + 1;
U32 matchEndIdx = current+8;
U32 matchEndIdx = current+8+1;
U32 dummy32; /* to be nullified at the end */
size_t bestLength = 0;
@ -233,7 +233,8 @@ static size_t ZSTD_insertBtAndFindBestMatch (
*smallerPtr = *largerPtr = 0;
zc->nextToUpdate = (matchEndIdx > current + 8) ? matchEndIdx - 8 : current+1; /* skip repetitive patterns */
assert(matchEndIdx > current+8);
zc->nextToUpdate = matchEndIdx - 8; /* skip repetitive patterns */
return bestLength;
}