ddidderr/zstd-rs
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factored the logic selecting lowest match index

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as suggested by @terrelln
This commit is contained in:
Yann Collet
2019-08-05 15:18:43 +02:00
parent 0b0b83e8f3
commit facbe8b2c2
5 changed files with 19 additions and 21 deletions
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lib/compress/zstd_compress_internal.h
+14 -1
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@@ -136,6 +136,8 @@ struct ZSTD_matchState_t {
ZSTD_window_t window; /* State for window round buffer management */
U32 loadedDictEnd; /* index of end of dictionary, within context's referential.
* When loadedDictEnd != 0, a dictionary is in use, and still valid.
* This relies on a mechanism to set loadedDictEnd=0 when dictionary is no longer within distance.
* Such mechanism is provided within ZSTD_window_enforceMaxDist() and ZSTD_checkDictValidity().
* When dict referential is copied into active context (i.e. not attached),
* loadedDictEnd == dictSize, since referential starts from zero.
*/
@@ -354,7 +356,7 @@ MEM_STATIC void ZSTD_storeSeq(seqStore_t* seqStorePtr, size_t litLength, const v
/* copy Literals */
assert(seqStorePtr->maxNbLit <= 128 KB);
assert(seqStorePtr->lit + litLength <= seqStorePtr->litStart + seqStorePtr->maxNbLit);
ZSTD_wildcopy(seqStorePtr->lit, literals, litLength, ZSTD_no_overlap);
ZSTD_wildcopy(seqStorePtr->lit, literals, (ptrdiff_t)litLength, ZSTD_no_overlap);
seqStorePtr->lit += litLength;
/* literal Length */
@@ -839,6 +841,17 @@ MEM_STATIC U32 ZSTD_window_update(ZSTD_window_t* window,
return contiguous;
}
MEM_STATIC U32 ZSTD_getLowestMatchIndex(const ZSTD_matchState_t* ms, U32 current, unsigned windowLog)
{
U32 const maxDistance = 1U << windowLog;
U32 const lowestValid = ms->window.lowLimit;
U32 const withinWindow = (current - lowestValid > maxDistance) ? current - maxDistance : lowestValid;
U32 const isDictionary = (ms->loadedDictEnd != 0);
U32 const matchLowest = isDictionary ? lowestValid : withinWindow;
return matchLowest;
}
/* debug functions */
#if (DEBUGLEVEL>=2)
lib/compress/zstd_double_fast.c
+2 -5
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@@ -65,6 +65,7 @@ size_t ZSTD_compressBlock_doubleFast_generic(
const U32 endIndex = (U32)((size_t)(istart - base) + srcSize);
const U32 lowestValid = ms->window.dictLimit;
const U32 maxDistance = 1U << cParams->windowLog;
/* presumes that, if there is a dictionary, it must be using Attach mode */
const U32 prefixLowestIndex = (endIndex - lowestValid > maxDistance) ? endIndex - maxDistance : lowestValid;
const BYTE* const prefixLowest = base + prefixLowestIndex;
const BYTE* const iend = istart + srcSize;
@@ -369,11 +370,7 @@ static size_t ZSTD_compressBlock_doubleFast_extDict_generic(
const BYTE* const ilimit = iend - 8;
const BYTE* const base = ms->window.base;
const U32 endIndex = (U32)((size_t)(istart - base) + srcSize);
const U32 maxDistance = 1U << cParams->windowLog;
const U32 validLowest = ms->window.lowLimit;
const int isDictionary = (ms->loadedDictEnd != 0);
const U32 withinWindow = (endIndex - validLowest > maxDistance) ? endIndex - maxDistance : validLowest;
const U32 lowLimit = isDictionary ? validLowest : withinWindow;
const U32 lowLimit = ZSTD_getLowestMatchIndex(ms, endIndex, cParams->windowLog);
const U32 dictStartIndex = lowLimit;
const U32 dictLimit = ms->window.dictLimit;
const U32 prefixStartIndex = (dictLimit > lowLimit) ? dictLimit : lowLimit;
lib/compress/zstd_fast.c
+1 -5
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@@ -381,11 +381,7 @@ static size_t ZSTD_compressBlock_fast_extDict_generic(
const BYTE* ip = istart;
const BYTE* anchor = istart;
const U32 endIndex = (U32)((size_t)(istart - base) + srcSize);
const U32 maxDistance = 1U << cParams->windowLog;
const U32 validLowest = ms->window.lowLimit;
const int isDictionary = (ms->loadedDictEnd != 0);
const U32 withinWindow = (endIndex - validLowest > maxDistance) ? endIndex - maxDistance : validLowest;
const U32 lowLimit = isDictionary ? validLowest : withinWindow;
const U32 lowLimit = ZSTD_getLowestMatchIndex(ms, endIndex, cParams->windowLog);
const U32 dictStartIndex = lowLimit;
const BYTE* const dictStart = dictBase + dictStartIndex;
const U32 dictLimit = ms->window.dictLimit;
lib/compress/zstd_lazy.c
+1 -5
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@@ -242,11 +242,7 @@ ZSTD_DUBT_findBestMatch(ZSTD_matchState_t* ms,
const BYTE* const base = ms->window.base;
U32 const current = (U32)(ip-base);
U32 const maxDistance = 1U << cParams->windowLog;
U32 const lowestValid = ms->window.lowLimit;
U32 const withinWindow = (current - lowestValid > maxDistance) ? current - maxDistance : lowestValid;
U32 const isDictionary = (ms->loadedDictEnd != 0);
U32 const windowLow = isDictionary ? lowestValid : withinWindow;
U32 const windowLow = ZSTD_getLowestMatchIndex(ms, current, cParams->windowLog);
U32* const bt = ms->chainTable;
U32 const btLog = cParams->chainLog - 1;
lib/compress/zstd_opt.c
+1 -5
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@@ -552,7 +552,6 @@ U32 ZSTD_insertBtAndGetAllMatches (
{
const ZSTD_compressionParameters* const cParams = &ms->cParams;
U32 const sufficient_len = MIN(cParams->targetLength, ZSTD_OPT_NUM -1);
U32 const maxDistance = 1U << cParams->windowLog;
const BYTE* const base = ms->window.base;
U32 const current = (U32)(ip-base);
U32 const hashLog = cParams->hashLog;
@@ -569,10 +568,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
const BYTE* const dictEnd = dictBase + dictLimit;
const BYTE* const prefixStart = base + dictLimit;
U32 const btLow = (btMask >= current) ? 0 : current - btMask;
U32 const lowestValid = ms->window.lowLimit;
U32 const withinWindow = (current - lowestValid > maxDistance) ? current - maxDistance : lowestValid;
U32 const isDictionary = (ms->loadedDictEnd != 0);
U32 const windowLow = isDictionary ? lowestValid : withinWindow;
U32 const windowLow = ZSTD_getLowestMatchIndex(ms, current, cParams->windowLog);
U32 const matchLow = windowLow ? windowLow : 1;
U32* smallerPtr = bt + 2*(current&btMask);
U32* largerPtr = bt + 2*(current&btMask) + 1;