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Find Proper Matches

dev
W. Felix Handte 2018-06-14 15:54:03 -04:00
parent 64348a15f1
commit 2091f34e9e
1 changed files with 44 additions and 3 deletions
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47
lib/compress/zstd_opt.c
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@ -664,9 +664,10 @@ U32 ZSTD_insertBtAndGetAllMatches (
matches[mnum].off = (current - matchIndex) + ZSTD_REP_MOVE;
matches[mnum].len = (U32)matchLength;
mnum++;
if (matchLength > ZSTD_OPT_NUM) break;
if (ip+matchLength == iLimit) { /* equal : no way to know if inf or sup */
break; /* drop, to preserve bt consistency (miss a little bit of compression) */
if ( matchLength > ZSTD_OPT_NUM
| ip+matchLength == iLimit /* equal : no way to know if inf or sup */) {
if (dictMode == ZSTD_dictMatchState) nbCompares = 0; /* break should also skip searching dms */
break; /* drop, to preserve bt consistency (miss a little bit of compression) */
}
}
@ -687,6 +688,46 @@ U32 ZSTD_insertBtAndGetAllMatches (
*smallerPtr = *largerPtr = 0;
commonLengthSmaller = commonLengthLarger = 0;
if (dictMode == ZSTD_dictMatchState && nbCompares) {
U32 dictMatchIndex = dms->hashTable[h];
const U32* const dmsBt = dms->chainTable;
while (nbCompares-- && (dictMatchIndex > dmsLowLimit)) {
const U32* const nextPtr = dmsBt + 2*(dictMatchIndex & btMask);
size_t matchLength = MIN(commonLengthSmaller, commonLengthLarger); /* guaranteed minimum nb of common bytes */
const BYTE* match = dmsBase + dictMatchIndex;
matchLength += ZSTD_count_2segments(ip+matchLength, match+matchLength, iLimit, dmsEnd, prefixStart);
if (dictMatchIndex+matchLength >= dmsHighLimit)
match = base + dictMatchIndex + dmsIndexDelta; /* to prepare for next usage of match[matchLength] */
if (matchLength > bestLength) {
matchIndex = dictMatchIndex + dmsIndexDelta;
if (matchLength > matchEndIdx - matchIndex)
matchEndIdx = matchIndex + (U32)matchLength;
bestLength = matchLength;
matches[mnum].off = (current - matchIndex) + ZSTD_REP_MOVE;
matches[mnum].len = (U32)matchLength;
mnum++;
if ( matchLength > ZSTD_OPT_NUM
| ip+matchLength == iLimit /* 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];
}
}
}
assert(matchEndIdx > current+8);
ms->nextToUpdate = matchEndIdx - 8; /* skip repetitive patterns */
return mnum;