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Merge pull request #2405 from senhuang42/sequence_compression_minmatch_fix

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Sequence Compression API - make validator use cctx minMatch instead of global MINMATCH
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sen 2020-12-01 17:34:01 -05:00 committed by GitHub
commit 993baba315
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3 changed files with 17 additions and 12 deletions
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21
lib/compress/zstd_compress.c
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@ -4524,7 +4524,7 @@ typedef struct {
/* Returns a ZSTD error code if sequence is not valid */
static size_t ZSTD_validateSequence(U32 offCode, U32 matchLength,
size_t posInSrc, U32 windowLog, size_t dictSize) {
size_t posInSrc, U32 windowLog, size_t dictSize, U32 minMatch) {
size_t offsetBound;
U32 windowSize = 1 << windowLog;
/* posInSrc represents the amount of data the the decoder would decode up to this point.
@ -4534,7 +4534,7 @@ static size_t ZSTD_validateSequence(U32 offCode, U32 matchLength,
*/
offsetBound = posInSrc > windowSize ? (size_t)windowSize : posInSrc + (size_t)dictSize;
RETURN_ERROR_IF(offCode > offsetBound + ZSTD_REP_MOVE, corruption_detected, "Offset too large!");
RETURN_ERROR_IF(matchLength < MINMATCH, corruption_detected, "Matchlength too small");
RETURN_ERROR_IF(matchLength < minMatch, corruption_detected, "Matchlength too small");
return 0;
}
@ -4594,7 +4594,8 @@ static size_t ZSTD_copySequencesToSeqStoreExplicitBlockDelim(ZSTD_CCtx* cctx, ZS
if (cctx->appliedParams.validateSequences) {
seqPos->posInSrc += litLength + matchLength;
FORWARD_IF_ERROR(ZSTD_validateSequence(offCode, matchLength, seqPos->posInSrc,
cctx->appliedParams.cParams.windowLog, dictSize),
cctx->appliedParams.cParams.windowLog, dictSize,
cctx->appliedParams.cParams.minMatch),
"Sequence validation failed");
}
ZSTD_storeSeq(&cctx->seqStore, litLength, ip, iend, offCode, matchLength - MINMATCH);
@ -4679,13 +4680,13 @@ static size_t ZSTD_copySequencesToSeqStoreNoBlockDelim(ZSTD_CCtx* cctx, ZSTD_seq
U32 firstHalfMatchLength;
litLength = startPosInSequence >= litLength ? 0 : litLength - startPosInSequence;
firstHalfMatchLength = endPosInSequence - startPosInSequence - litLength;
if (matchLength > blockSize && firstHalfMatchLength >= MINMATCH) {
if (matchLength > blockSize && firstHalfMatchLength >= cctx->appliedParams.cParams.minMatch) {
/* Only ever split the match if it is larger than the block size */
U32 secondHalfMatchLength = currSeq.matchLength + currSeq.litLength - endPosInSequence;
if (secondHalfMatchLength < MINMATCH) {
/* Move the endPosInSequence backward so that it creates match of MINMATCH length */
endPosInSequence -= MINMATCH - secondHalfMatchLength;
bytesAdjustment = MINMATCH - secondHalfMatchLength;
if (secondHalfMatchLength < cctx->appliedParams.cParams.minMatch) {
/* Move the endPosInSequence backward so that it creates match of minMatch length */
endPosInSequence -= cctx->appliedParams.cParams.minMatch - secondHalfMatchLength;
bytesAdjustment = cctx->appliedParams.cParams.minMatch - secondHalfMatchLength;
firstHalfMatchLength -= bytesAdjustment;
}
matchLength = firstHalfMatchLength;
@ -4716,7 +4717,8 @@ static size_t ZSTD_copySequencesToSeqStoreNoBlockDelim(ZSTD_CCtx* cctx, ZSTD_seq
if (cctx->appliedParams.validateSequences) {
seqPos->posInSrc += litLength + matchLength;
FORWARD_IF_ERROR(ZSTD_validateSequence(offCode, matchLength, seqPos->posInSrc,
cctx->appliedParams.cParams.windowLog, dictSize),
cctx->appliedParams.cParams.windowLog, dictSize,
cctx->appliedParams.cParams.minMatch),
"Sequence validation failed");
}
DEBUGLOG(6, "Storing sequence: (of: %u, ml: %u, ll: %u)", offCode, matchLength, litLength);
@ -4884,6 +4886,7 @@ size_t ZSTD_compressSequences(ZSTD_CCtx* const cctx, void* dst, size_t dstCapaci
DEBUGLOG(3, "ZSTD_compressSequences()");
assert(cctx != NULL);
FORWARD_IF_ERROR(ZSTD_CCtx_init_compressStream2(cctx, ZSTD_e_end, srcSize), "CCtx initialization failed");
RETURN_ERROR_IF(inSeqsSize > cctx->seqStore.maxNbSeq, memory_allocation, "Not enough memory allocated. Try adjusting ZSTD_c_minMatch.");
/* Begin writing output, starting with frame header */
frameHeaderSize = ZSTD_writeFrameHeader(op, dstCapacity, &cctx->appliedParams, srcSize, cctx->dictID);
op += frameHeaderSize;

7
lib/zstd.h
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@ -1356,9 +1356,10 @@ ZSTDLIB_API size_t ZSTD_mergeBlockDelimiters(ZSTD_Sequence* sequences, size_t se
* behavior. If ZSTD_c_validateSequences == 1, then if sequence is invalid (see doc/zstd_compression_format.md for
* specifics regarding offset/matchlength requirements) then the function will bail out and return an error.
*
* In addition to the two adjustable experimental params, other noteworthy cctx parameters are the compression level and window log.
* - The compression level accordingly adjusts the strength of the entropy coder, as it would in typical compression.
* - The window log affects offset validation: this function will return an error at higher debug levels if a provided offset
* In addition to the two adjustable experimental params, there are other important cctx params.
* - ZSTD_c_minMatch MUST be set as less than or equal to the smallest match generated by the match finder. It has a minimum value of ZSTD_MINMATCH_MIN.
* - ZSTD_c_compressionLevel accordingly adjusts the strength of the entropy coder, as it would in typical compression.
* - ZSTD_c_windowLog affects offset validation: this function will return an error at higher debug levels if a provided offset
* is larger than what the spec allows for a given window log and dictionary (if present). See: doc/zstd_compression_format.md
*
* Note: Repcodes are, as of now, always re-calculated within this function, so ZSTD_Sequence::rep is unused.

1
tests/fuzz/sequence_compression_api.c
View File

@ -199,6 +199,7 @@ static size_t roundTripTest(void *result, size_t resultCapacity,
ZSTD_CCtx_setParameter(cctx, ZSTD_c_compressionLevel, cLevel);
ZSTD_CCtx_setParameter(cctx, ZSTD_c_windowLog, wLog);
ZSTD_CCtx_setParameter(cctx, ZSTD_c_minMatch, ZSTD_MINMATCH_MIN);
ZSTD_CCtx_setParameter(cctx, ZSTD_c_validateSequences, 1);
/* TODO: Add block delim mode fuzzing */
ZSTD_CCtx_setParameter(cctx, ZSTD_c_blockDelimiters, ZSTD_sf_noBlockDelimiters);
if (hasDict) {