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Avoid Searching Dictionary in ZSTD_btlazy2 When an Optimal Match is Found

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Bailing here is important to avoid reading past the end of the input buffer.
This commit is contained in:
W. Felix Handte 2018-10-08 15:56:09 -07:00
parent d121b3451c
commit b8235be865
1 changed files with 11 additions and 2 deletions
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13
lib/compress/zstd_lazy.c
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@ -147,6 +147,7 @@ ZSTD_DUBT_findBetterDictMatch (
ZSTD_matchState_t* ms, ZSTD_matchState_t* ms,
const BYTE* const ip, const BYTE* const iend, const BYTE* const ip, const BYTE* const iend,
size_t* offsetPtr, size_t* offsetPtr,
size_t bestLength,
U32 nbCompares, U32 nbCompares,
U32 const mls, U32 const mls,
const ZSTD_dictMode_e dictMode) const ZSTD_dictMode_e dictMode)
@ -172,7 +173,7 @@ ZSTD_DUBT_findBetterDictMatch (
U32 const btMask = (1 << btLog) - 1; U32 const btMask = (1 << btLog) - 1;
U32 const btLow = (btMask >= dictHighLimit - dictLowLimit) ? dictLowLimit : dictHighLimit - btMask; U32 const btLow = (btMask >= dictHighLimit - dictLowLimit) ? dictLowLimit : dictHighLimit - btMask;
size_t commonLengthSmaller=0, commonLengthLarger=0, bestLength=0; size_t commonLengthSmaller=0, commonLengthLarger=0;
(void)dictMode; (void)dictMode;
assert(dictMode == ZSTD_dictMatchState); assert(dictMode == ZSTD_dictMatchState);
@ -319,6 +320,11 @@ ZSTD_DUBT_findBestMatch(ZSTD_matchState_t* ms,
if ( (4*(int)(matchLength-bestLength)) > (int)(ZSTD_highbit32(current-matchIndex+1) - ZSTD_highbit32((U32)offsetPtr[0]+1)) ) if ( (4*(int)(matchLength-bestLength)) > (int)(ZSTD_highbit32(current-matchIndex+1) - ZSTD_highbit32((U32)offsetPtr[0]+1)) )
bestLength = matchLength, *offsetPtr = ZSTD_REP_MOVE + current - matchIndex; bestLength = matchLength, *offsetPtr = ZSTD_REP_MOVE + current - matchIndex;
if (ip+matchLength == iend) { /* equal : no way to know if inf or sup */ if (ip+matchLength == iend) { /* equal : no way to know if inf or sup */
if (dictMode == ZSTD_dictMatchState) {
nbCompares = 0; /* in addition to avoiding checking any
* further in this loop, make sure we
* skip checking in the dictionary. */
}
break; /* drop, to guarantee consistency (miss a little bit of compression) */ break; /* drop, to guarantee consistency (miss a little bit of compression) */
} }
} }
@ -342,7 +348,10 @@ ZSTD_DUBT_findBestMatch(ZSTD_matchState_t* ms,
*smallerPtr = *largerPtr = 0; *smallerPtr = *largerPtr = 0;
if (dictMode == ZSTD_dictMatchState && nbCompares) { if (dictMode == ZSTD_dictMatchState && nbCompares) {
bestLength = ZSTD_DUBT_findBetterDictMatch(ms, ip, iend, offsetPtr, nbCompares, mls, dictMode); bestLength = ZSTD_DUBT_findBetterDictMatch(
ms, ip, iend,
offsetPtr, bestLength, nbCompares,
mls, dictMode);
} }
assert(matchEndIdx > current+8); /* ensure nextToUpdate is increased */ assert(matchEndIdx > current+8); /* ensure nextToUpdate is increased */