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Search Dict for Matches

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This commit is contained in:
W. Felix Handte 2018-06-12 18:38:10 -04:00
parent ace9cfa950
commit 0551de4b5a
1 changed files with 82 additions and 0 deletions
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82
lib/compress/zstd_lazy.c
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@ -140,6 +140,84 @@ static void ZSTD_insertDUBT1(
}
static size_t ZSTD_DUBT_findBetterDictMatch (
ZSTD_matchState_t* ms, ZSTD_compressionParameters const* cParams,
const BYTE* const ip, const BYTE* const iend,
size_t* offsetPtr,
size_t bestLength,
U32 nbCompares,
U32 const mls,
const ZSTD_dictMode_e dictMode) {
const ZSTD_matchState_t * const dms = ms->dictMatchState;
const U32 * const dictHashTable = dms->hashTable;
U32 const hashLog = cParams->hashLog;
size_t const h = ZSTD_hashPtr(ip, hashLog, mls);
U32 dictMatchIndex = dictHashTable[h];
const BYTE* const base = ms->window.base;
const BYTE* const prefixStart = base + ms->window.dictLimit;
U32 const current = (U32)(ip-base);
const BYTE* const dictBase = dms->window.base;
const BYTE* const dictEnd = dms->window.nextSrc;
U32 const dictHighLimit = (U32)(dms->window.nextSrc - dms->window.base);
U32 const dictLowLimit = dms->window.lowLimit;
U32 const dictIndexDelta = ms->window.lowLimit - dictHighLimit;
U32* const dictBt = dms->chainTable;
U32 const btLog = cParams->chainLog - 1;
U32 const btMask = (1 << btLog) - 1;
U32 const btLow = (btMask >= dictHighLimit - dictLowLimit) ? 0 : dictHighLimit - btMask;
size_t commonLengthSmaller=0, commonLengthLarger=0;
U32 matchEndIdx = current+8+1;
(void)dictMode;
assert(dictMode == ZSTD_dictMatchState);
while (nbCompares-- && (dictMatchIndex > dictLowLimit)) {
U32* const nextPtr = dictBt + 2*(dictMatchIndex & btMask);
size_t matchLength = MIN(commonLengthSmaller, commonLengthLarger); /* guaranteed minimum nb of common bytes */
const BYTE* match = dictBase + dictMatchIndex;
matchLength += ZSTD_count_2segments(ip+matchLength, match+matchLength, iend, dictEnd, prefixStart);
if (dictMatchIndex+matchLength >= dictHighLimit)
match = base + dictMatchIndex + dictIndexDelta; /* to prepare for next usage of match[matchLength] */
if (matchLength > bestLength) {
U32 matchIndex = dictMatchIndex + dictIndexDelta;
if (matchLength > matchEndIdx - matchIndex)
matchEndIdx = matchIndex + (U32)matchLength;
if ( (4*(int)(matchLength-bestLength)) > (int)(ZSTD_highbit32(current-matchIndex+1) - ZSTD_highbit32((U32)offsetPtr[0]+1)) ) {
DEBUGLOG(9, "ZSTD_DUBT_findBestDictMatch(%u) : found better match length %u -> %u and offsetCode %u -> %u (dictMatchIndex %u, matchIndex %u)",
current, (U32)bestLength, (U32)matchLength, (U32)*offsetPtr, ZSTD_REP_MOVE + current - matchIndex, dictMatchIndex, matchIndex);
bestLength = matchLength, *offsetPtr = ZSTD_REP_MOVE + current - matchIndex;
}
if (ip+matchLength == iend) { /* equal : no way to know if inf or sup */
break; /* drop, to guarantee consistency (miss a little bit of compression) */
}
}
if (match[matchLength] < ip[matchLength]) {
if (dictMatchIndex <= btLow) { break; } /* beyond tree size, stop the search */
commonLengthSmaller = matchLength; /* all smaller will now have at least this guaranteed common length */
dictMatchIndex = nextPtr[1]; /* new matchIndex larger than previous (closer to current) */
} else {
/* match is larger than current */
if (dictMatchIndex <= btLow) { break; } /* beyond tree size, stop the search */
commonLengthLarger = matchLength;
dictMatchIndex = nextPtr[0];
}
}
if (bestLength >= MINMATCH) {
U32 const mIndex = current - ((U32)*offsetPtr - ZSTD_REP_MOVE); (void)mIndex;
DEBUGLOG(8, "ZSTD_DUBT_findBestDictMatch(%u) : found match of length %u and offsetCode %u (pos %u)",
current, (U32)bestLength, (U32)*offsetPtr, mIndex);
}
return bestLength;
}
static size_t ZSTD_DUBT_findBestMatch (
ZSTD_matchState_t* ms, ZSTD_compressionParameters const* cParams,
const BYTE* const ip, const BYTE* const iend,
@ -261,6 +339,10 @@ static size_t ZSTD_DUBT_findBestMatch (
*smallerPtr = *largerPtr = 0;
if (dictMode == ZSTD_dictMatchState && nbCompares) {
bestLength = ZSTD_DUBT_findBetterDictMatch(ms, cParams, ip, iend, offsetPtr, bestLength, nbCompares, mls, dictMode);
}
assert(matchEndIdx > current+8); /* ensure nextToUpdate is increased */
ms->nextToUpdate = matchEndIdx - 8; /* skip repetitive patterns */
if (bestLength >= MINMATCH) {