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small PA optimization

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which measurably improves speed
on levels 9+
This commit is contained in:
Yann Collet 2018-05-06 16:47:31 -07:00
parent cdb0275b7f
commit 24b9c485db
1 changed files with 18 additions and 11 deletions
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29
lib/lz4hc.c
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@ -291,15 +291,12 @@ LZ4HC_InsertAndGetWiderMatch (
if (candidateDist > distanceToNextMatch) {
distanceToNextMatch = candidateDist;
matchChainPos = pos;
}
}
} }
if (distanceToNextMatch > 1) {
if (distanceToNextMatch > matchIndex) break; /* avoid overflow */
matchIndex -= distanceToNextMatch;
continue;
}
}
}
} } }
{ U32 const distNextMatch = DELTANEXTU16(chainTable, matchIndex);
if (patternAnalysis && distNextMatch==1 && matchChainPos==0) {
@ -309,7 +306,7 @@ LZ4HC_InsertAndGetWiderMatch (
if ( ((pattern & 0xFFFF) == (pattern >> 16))
& ((pattern & 0xFF) == (pattern >> 24)) ) {
repeat = rep_confirmed;
srcPatternLength = LZ4HC_countPattern(ip+4, iHighLimit, pattern) + 4;
srcPatternLength = LZ4HC_countPattern(ip+sizeof(pattern), iHighLimit, pattern) + sizeof(pattern);
} else {
repeat = rep_not;
} }
@ -318,19 +315,29 @@ LZ4HC_InsertAndGetWiderMatch (
const BYTE* const matchPtr = base + matchCandidateIdx;
if (LZ4_read32(matchPtr) == pattern) { /* good candidate */
size_t const forwardPatternLength = LZ4HC_countPattern(matchPtr+sizeof(pattern), iHighLimit, pattern) + sizeof(pattern);
const BYTE* const maxLowPtr = (lowPrefixPtr + MAX_DISTANCE >= ip) ? lowPrefixPtr : ip - MAX_DISTANCE;
size_t const backLength = LZ4HC_reverseCountPattern(matchPtr, maxLowPtr, pattern);
const BYTE* const lowestMatchPtr = (lowPrefixPtr + MAX_DISTANCE >= ip) ? lowPrefixPtr : ip - MAX_DISTANCE;
size_t const backLength = LZ4HC_reverseCountPattern(matchPtr, lowestMatchPtr, pattern);
size_t const currentSegmentLength = backLength + forwardPatternLength;
if ( (currentSegmentLength >= srcPatternLength) /* current pattern segment large enough to contain full srcPatternLength */
&& (forwardPatternLength <= srcPatternLength) ) { /* haven't reached this position yet */
matchIndex = matchCandidateIdx + (U32)forwardPatternLength - (U32)srcPatternLength; /* best position, full pattern, might be followed by more match */
} else {
matchIndex = matchCandidateIdx - (U32)backLength; /* let's go to farthest segment position, will find a match of length currentSegmentLength + maybe some back */
}
matchIndex = matchCandidateIdx - (U32)backLength; /* farthest position in current segment, will find a match of length currentSegmentLength + maybe some back */
if (lookBackLength==0) { /* no back possible */
size_t const maxML = MIN(currentSegmentLength, srcPatternLength);
if ((size_t)longest < maxML) {
longest = maxML;
*matchpos = base + matchIndex; /* virtual pos, relative to ip, to retrieve offset */
*startpos = ip;
}
{ U32 const distToNextPattern = DELTANEXTU16(chainTable, matchIndex);
if (distToNextPattern > matchIndex) break; /* avoid overflow */
matchIndex -= distToNextPattern;
} } }
continue;
} }
} }
} } /* PA optimization */
/* follow current chain */
matchIndex -= DELTANEXTU16(chainTable, matchIndex+matchChainPos);