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[LZ4HC] Speed up pattern compression with external dictionary

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Fixes #761.
This commit is contained in:
Nick Terrell 2019-07-23 17:54:09 -07:00
parent 805947ffcb
commit 4c1d4c437d
1 changed files with 46 additions and 26 deletions
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72
lib/lz4hc.c
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@ -151,6 +151,19 @@ int LZ4HC_countBack(const BYTE* const ip, const BYTE* const match,
return back;
}
#if defined(_MSC_VER)
# define LZ4HC_rotl32(x,r) _rotl(x,r)
#else
# define LZ4HC_rotl32(x,r) ((x << r) | (x >> (32 - r)))
#endif
static U32 LZ4HC_rotatePattern(size_t const length, U32 const pattern)
{
size_t const bitsToRotate = (length & (sizeof(pattern) - 1)) << 3;
return LZ4HC_rotl32(pattern, (int)bitsToRotate);
}
/* LZ4HC_countPattern() :
* pattern32 must be a sample of repetitive pattern of length 1, 2 or 4 (but not 3!) */
static unsigned
@ -313,34 +326,41 @@ LZ4HC_InsertAndGetWiderMatch (
} else {
repeat = rep_not;
} }
if ( (repeat == rep_confirmed)
&& (matchCandidateIdx >= dictLimit) ) { /* same segment only */
const BYTE* const matchPtr = base + matchCandidateIdx;
if ( (repeat == rep_confirmed) && (matchCandidateIdx >= lowestMatchIndex) ) {
const int extDict = matchCandidateIdx < dictLimit;
const BYTE* const matchPtr = (extDict ? dictBase : 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 lowestMatchPtr = (lowPrefixPtr + LZ4_DISTANCE_MAX >= ip) ? lowPrefixPtr : ip - LZ4_DISTANCE_MAX;
size_t const backLength = LZ4HC_reverseCountPattern(matchPtr, lowestMatchPtr, pattern);
size_t const currentSegmentLength = backLength + forwardPatternLength;
const BYTE* const dictStart = dictBase + hc4->lowLimit;
const BYTE* const iLimit = extDict ? dictBase + dictLimit : iHighLimit;
size_t forwardPatternLength = LZ4HC_countPattern(matchPtr+sizeof(pattern), iLimit, pattern) + sizeof(pattern);
if (extDict && ip + forwardPatternLength == iLimit) {
U32 const rotatedPattern = LZ4HC_rotatePattern(forwardPatternLength, pattern);
forwardPatternLength += LZ4HC_countPattern(lowPrefixPtr, iHighLimit, rotatedPattern);
}
{ const BYTE* const lowestMatchPtr = extDict ? dictStart : lowPrefixPtr;
size_t const backLengthRaw = LZ4HC_reverseCountPattern(matchPtr, lowestMatchPtr, pattern);
size_t const backLength = matchCandidateIdx - MAX(matchCandidateIdx - (U32)backLengthRaw, lowestMatchIndex);
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; /* 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) {
assert(base + matchIndex < ip);
if (ip - (base+matchIndex) > LZ4_DISTANCE_MAX) break;
assert(maxML < 2 GB);
longest = (int)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;
} } }
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; /* 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) {
assert(base + matchIndex < ip);
if (ip - (base+matchIndex) > LZ4_DISTANCE_MAX) break;
assert(maxML < 2 GB);
longest = (int)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 */