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Correct the detection of mismatched repcodes

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This commit is contained in:
Sen Huang 2021-04-09 08:01:54 -07:00
parent f71aabb5b5
commit 550f76f131
2 changed files with 26 additions and 13 deletions
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2
lib/common/zstd_internal.h
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@ -352,7 +352,7 @@ typedef enum {
* Private declarations
*********************************************/
typedef struct seqDef_s {
U32 offset; /* Offset code of the sequence */
U32 offset; /* offset == rawOffset + ZSTD_REP_NUM, or equivalently, offCode + 1 */
U16 litLength;
U16 matchLength;
} seqDef;

37
lib/compress/zstd_compress.c
View File

@ -3180,6 +3180,21 @@ static void ZSTD_deriveSeqStoreChunk(seqStore_t* resultSeqStore,
resultSeqStore->ofCode += startIdx;
}
/**
* Returns the raw offset represented by the combination of offCode, ll0, and repcode history.
* offCode must be an offCode representing a repcode, therefore in the range of [0, 2].
*/
static U32 ZSTD_resolveRepcodeToRawOffset(const U32 rep[ZSTD_REP_NUM], const U32 offCode, const U32 ll0) {
U32 const adjustedOffCode = offCode + ll0;
assert(offCode < ZSTD_REP_NUM);
if (adjustedOffCode == ZSTD_REP_NUM) {
/* litlength == 0 and offCode == 2 implies selection of first repcode - 1 */
assert(rep[0] > 0);
return rep[0] - 1;
}
return rep[adjustedOffCode];
}
/**
* ZSTD_seqStore_resolveOffCodes() reconciles any possible divergences in offset history that may arise
* due to emission of RLE/raw blocks that disturb the offset history, and replaces any repcodes within
@ -3196,23 +3211,21 @@ static void ZSTD_seqStore_resolveOffCodes(repcodes_t* const dRepcodes, repcodes_
U32 const ll0 = (seq->litLength == 0);
U32 offCode = seq->offset - 1;
assert(seq->offset > 0);
if (offCode <= ZSTD_REP_MOVE && (dRepcodes->rep[offCode] != cRepcodes->rep[offCode])) {
if (offCode <= ZSTD_REP_MOVE) {
U32 const dRawOffset = ZSTD_resolveRepcodeToRawOffset(dRepcodes->rep, offCode, ll0);
U32 const cRawOffset = ZSTD_resolveRepcodeToRawOffset(cRepcodes->rep, offCode, ll0);
/* Adjust simulated decompression repcode history if we come across a mismatch. Replace
* the repcode with the offset it actually references, determined by the compression
* repcode history.
*/
offCode += ll0;
if (offCode == ZSTD_REP_MOVE+1) {
/* litlength == 0 and offset_value = 3 implies selection of first repcode - 1 */
seq->offset = (cRepcodes->rep[0] + ZSTD_REP_NUM) - 1;
} else {
seq->offset = cRepcodes->rep[offCode] + ZSTD_REP_NUM;
if (dRawOffset != cRawOffset) {
seq->offset = cRawOffset + ZSTD_REP_NUM;
}
*dRepcodes = ZSTD_updateRep(dRepcodes->rep, seq->offset - 1, ll0);
} else {
*dRepcodes = ZSTD_updateRep(dRepcodes->rep, offCode, ll0);
}
/* Compression repcode history is always updated with values directly from the seqStore */
/* Compression repcode history is always updated with values directly from the unmodified seqStore.
* Decompression repcode history may use modified seq->offset value taken from compression repcode history.
*/
*dRepcodes = ZSTD_updateRep(dRepcodes->rep, seq->offset - 1, ll0);
*cRepcodes = ZSTD_updateRep(cRepcodes->rep, offCode, ll0);
}
}
@ -3351,7 +3364,7 @@ static size_t ZSTD_deriveBlockSplits(ZSTD_CCtx* zc, U32 partitions[], U32 nbSeq)
}
ZSTD_deriveBlockSplitsHelper(&splits, 0, nbSeq, zc, &zc->seqStore);
splits.splitLocations[splits.idx] = nbSeq;
DEBUGLOG(5, "ZSTD_deriveBlockSplits: final nb splits: %zu", splits.idx-1);
DEBUGLOG(5, "ZSTD_deriveBlockSplits: final nb partitions: %zu", splits.idx+1);
return splits.idx;
}