AuroraMiddleware/lz4
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lz4hc: SC only enabled for opt parser

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the trade off is not good for regular HC parser :
compression is a little bit better, but speed cost is too large in comparison.
This commit is contained in:
Yann Collet 2018-05-05 14:10:30 -07:00
parent d097bf93f8
commit a4e918d7a6
1 changed files with 7 additions and 7 deletions
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14
lib/lz4hc.c
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@ -213,6 +213,7 @@ LZ4HC_InsertAndGetWiderMatch (
const BYTE** startpos,
const int maxNbAttempts,
const int patternAnalysis,
const int chainSwap,
const dictCtx_directive dict,
const HCfavor_e favorDecSpeed)
{
@ -280,8 +281,8 @@ LZ4HC_InsertAndGetWiderMatch (
*startpos = ip + back;
} } }
if ( lookBackLength==0 /* search forward only */
&& mlt==longest) { /* better match => select a better chain */
if (chainSwap && mlt==longest) { /* better match => select a better chain */
assert(lookBackLength==0); /* search forward only */
if (matchIndex + longest <= ipIndex) {
U32 distanceToNextMatch = 1;
int pos;
@ -327,7 +328,6 @@ LZ4HC_InsertAndGetWiderMatch (
} else {
matchIndex = matchCandidateIdx - (U32)backLength; /* let's go to farthest segment position, will find a match of length currentSegmentLength + maybe some back */
}
matchChainPos = 0;
continue;
} }
} }
@ -382,7 +382,7 @@ int LZ4HC_InsertAndFindBestMatch(LZ4HC_CCtx_internal* const hc4, /* Index tabl
/* note : LZ4HC_InsertAndGetWiderMatch() is able to modify the starting position of a match (*startpos),
* but this won't be the case here, as we define iLowLimit==ip,
* so LZ4HC_InsertAndGetWiderMatch() won't be allowed to search past ip */
return LZ4HC_InsertAndGetWiderMatch(hc4, ip, ip, iLimit, MINMATCH-1, matchpos, &uselessPtr, maxNbAttempts, patternAnalysis, dict, favorCompressionRatio);
return LZ4HC_InsertAndGetWiderMatch(hc4, ip, ip, iLimit, MINMATCH-1, matchpos, &uselessPtr, maxNbAttempts, 0 /* chainSwap */, patternAnalysis, dict, favorCompressionRatio);
}
@ -515,7 +515,7 @@ _Search2:
if (ip+ml <= mflimit) {
ml2 = LZ4HC_InsertAndGetWiderMatch(ctx,
ip + ml - 2, ip + 0, matchlimit, ml, &ref2, &start2,
maxNbAttempts, patternAnalysis, dict, favorCompressionRatio);
maxNbAttempts, 0, patternAnalysis, dict, favorCompressionRatio);
} else {
ml2 = ml;
}
@ -560,7 +560,7 @@ _Search3:
if (start2 + ml2 <= mflimit) {
ml3 = LZ4HC_InsertAndGetWiderMatch(ctx,
start2 + ml2 - 3, start2, matchlimit, ml2, &ref3, &start3,
maxNbAttempts, patternAnalysis, dict, favorCompressionRatio);
maxNbAttempts, 0, patternAnalysis, dict, favorCompressionRatio);
} else {
ml3 = ml2;
}
@ -1128,7 +1128,7 @@ LZ4HC_FindLongerMatch(LZ4HC_CCtx_internal* const ctx,
/* note : LZ4HC_InsertAndGetWiderMatch() is able to modify the starting position of a match (*startpos),
* but this won't be the case here, as we define iLowLimit==ip,
* so LZ4HC_InsertAndGetWiderMatch() won't be allowed to search past ip */
int matchLength = LZ4HC_InsertAndGetWiderMatch(ctx, ip, ip, iHighLimit, minLen, &matchPtr, &ip, nbSearches, 1 /* patternAnalysis */, dict, favorDecSpeed);
int matchLength = LZ4HC_InsertAndGetWiderMatch(ctx, ip, ip, iHighLimit, minLen, &matchPtr, &ip, nbSearches, 1 /*chainSwap*/, 1 /*patternAnalysis*/, dict, favorDecSpeed);
if (matchLength <= minLen) return match;
if (favorDecSpeed) {
if ((matchLength>18) & (matchLength<=36)) matchLength=18; /* favor shortcut */