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Correct and clarify repcode offset history logic

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This commit is contained in:
Elliot Gorokhovsky
2022-05-09 21:01:38 -04:00
parent 8bf32de850
commit 97aabc496e
3 changed files with 42 additions and 26 deletions
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lib/compress/zstd_lazy.c
+11 -6
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@@ -1461,7 +1461,8 @@ ZSTD_compressBlock_lazy_generic(
const BYTE* const prefixLowest = base + prefixLowestIndex;
searchMax_f const searchMax = ZSTD_selectLazyVTable(ms, searchMethod, dictMode)->searchMax;
U32 offset_1 = rep[0], offset_2 = rep[1], savedOffset=0;
U32 offset_1 = rep[0], offset_2 = rep[1];
U32 offsetSaved1 = 0, offsetSaved2 = 0;
const int isDMS = dictMode == ZSTD_dictMatchState;
const int isDDS = dictMode == ZSTD_dedicatedDictSearch;
@@ -1484,8 +1485,8 @@ ZSTD_compressBlock_lazy_generic(
U32 const curr = (U32)(ip - base);
U32 const windowLow = ZSTD_getLowestPrefixIndex(ms, curr, ms->cParams.windowLog);
U32 const maxRep = curr - windowLow;
if (offset_2 > maxRep) savedOffset = offset_2, offset_2 = 0;
if (offset_1 > maxRep) savedOffset = offset_1, offset_1 = 0;
if (offset_2 > maxRep) offsetSaved2 = offset_2, offset_2 = 0;
if (offset_1 > maxRep) offsetSaved1 = offset_1, offset_1 = 0;
}
if (isDxS) {
/* dictMatchState repCode checks don't currently handle repCode == 0
@@ -1681,9 +1682,13 @@ _storeSequence:
continue; /* faster when present ... (?) */
} } }
/* Save reps for next block */
rep[0] = offset_1 ? offset_1 : savedOffset;
rep[1] = offset_2 ? offset_2 : savedOffset;
/* If offset_1 started invalid (offsetSaved1 > 0) and became valid (offset_1 > 0),
* rotate saved offsets. */
offsetSaved2 = ((offsetSaved1 > 0) & (offset_1 > 0)) ? offsetSaved1 : offsetSaved2;
/* save reps for next block */
rep[0] = offset_1 ? offset_1 : offsetSaved1;
rep[1] = offset_2 ? offset_2 : offsetSaved2;
/* Return the last literals size */
return (size_t)(iend - anchor);