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constify MatchState* parameter when possible

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turns out, it's possible to constify MatchState* parameter
in some parts of the binary tree algorithm,
making it a pure read-only parameter,
as opposed to a mutable state.

This is supposed to be helpful for both maintenance and the compiler.
This commit is contained in:
Yann Collet 2021-09-23 08:27:44 -07:00
parent c7afbec4c1
commit fa2a4d77c7
3 changed files with 16 additions and 20 deletions
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10
lib/compress/zstd_compress_internal.h
View File

@ -1228,15 +1228,15 @@ MEM_STATIC U32 ZSTD_window_update(ZSTD_window_t* window,
*/
MEM_STATIC U32 ZSTD_getLowestMatchIndex(const ZSTD_matchState_t* ms, U32 curr, unsigned windowLog)
{
U32 const maxDistance = 1U << windowLog;
U32 const lowestValid = ms->window.lowLimit;
U32 const withinWindow = (curr - lowestValid > maxDistance) ? curr - maxDistance : lowestValid;
U32 const isDictionary = (ms->loadedDictEnd != 0);
U32 const maxDistance = 1U << windowLog;
U32 const lowestValid = ms->window.lowLimit;
U32 const withinWindow = (curr - lowestValid > maxDistance) ? curr - maxDistance : lowestValid;
U32 const isDictionary = (ms->loadedDictEnd != 0);
/* When using a dictionary the entire dictionary is valid if a single byte of the dictionary
* is within the window. We invalidate the dictionary (and set loadedDictEnd to 0) when it isn't
* valid for the entire block. So this check is sufficient to find the lowest valid match index.
*/
U32 const matchLowest = isDictionary ? lowestValid : withinWindow;
U32 const matchLowest = isDictionary ? lowestValid : withinWindow;
return matchLowest;
}

6
lib/compress/zstd_lazy.c
View File

@ -61,7 +61,7 @@ ZSTD_updateDUBT(ZSTD_matchState_t* ms,
* assumption : curr >= btlow == (curr - btmask)
* doesn't fail */
static void
ZSTD_insertDUBT1(ZSTD_matchState_t* ms,
ZSTD_insertDUBT1(const ZSTD_matchState_t* ms,
U32 curr, const BYTE* inputEnd,
U32 nbCompares, U32 btLow,
const ZSTD_dictMode_e dictMode)
@ -151,7 +151,7 @@ ZSTD_insertDUBT1(ZSTD_matchState_t* ms,
static size_t
ZSTD_DUBT_findBetterDictMatch (
ZSTD_matchState_t* ms,
const ZSTD_matchState_t* ms,
const BYTE* const ip, const BYTE* const iend,
size_t* offsetPtr,
size_t bestLength,
@ -868,7 +868,7 @@ FORCE_INLINE_TEMPLATE size_t ZSTD_HcFindBestMatch_extDict_selectMLS (
#define ZSTD_ROW_HASH_TAG_OFFSET 16 /* byte offset of hashes in the match state's tagTable from the beginning of a row */
#define ZSTD_ROW_HASH_TAG_BITS 8 /* nb bits to use for the tag */
#define ZSTD_ROW_HASH_TAG_MASK ((1u << ZSTD_ROW_HASH_TAG_BITS) - 1)
#define ZSTD_ROW_HASH_MAX_ENTRIES 64 /* absolute maximum number of entries per row, for all configurations */
#define ZSTD_ROW_HASH_MAX_ENTRIES 64 /* absolute maximum number of entries per row, for all configurations */
#define ZSTD_ROW_HASH_CACHE_MASK (ZSTD_ROW_HASH_CACHE_SIZE - 1)

20
lib/compress/zstd_opt.c
View File

@ -366,7 +366,7 @@ MEM_STATIC U32 ZSTD_readMINMATCH(const void* memPtr, U32 length)
/* Update hashTable3 up to ip (excluded)
Assumption : always within prefix (i.e. not within extDict) */
static U32 ZSTD_insertAndFindFirstIndexHash3 (ZSTD_matchState_t* ms,
static U32 ZSTD_insertAndFindFirstIndexHash3 (const ZSTD_matchState_t* ms,
U32* nextToUpdate3,
const BYTE* const ip)
{
@ -396,7 +396,7 @@ static U32 ZSTD_insertAndFindFirstIndexHash3 (ZSTD_matchState_t* ms,
* @param target The target of ZSTD_updateTree_internal() - we are filling to this position
* @return : nb of positions added */
static U32 ZSTD_insertBt1(
ZSTD_matchState_t* ms,
const ZSTD_matchState_t* ms,
const BYTE* const ip, const BYTE* const iend,
U32 const target,
U32 const mls, const int extDict)
@ -421,8 +421,8 @@ static U32 ZSTD_insertBt1(
U32* smallerPtr = bt + 2*(curr&btMask);
U32* largerPtr = smallerPtr + 1;
U32 dummy32; /* to be nullified at the end */
/* windowLow is based on target because we're only need positions that will be
* in the window at the end of the tree update.
/* windowLow is based on target because
* we only need positions that will be in the window at the end of the tree update.
*/
U32 const windowLow = ZSTD_getLowestMatchIndex(ms, target, cParams->windowLog);
U32 matchEndIdx = curr+8+1;
@ -669,7 +669,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
return 1;
} } }
/* no dictMatchState lookup: dicts don't have a populated HC3 table */
}
} /* if (mls == 3) */
hashTable[h] = curr; /* Update Hash Table */
@ -706,8 +706,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
| (ip+matchLength == iLimit) /* equal : no way to know if inf or sup */) {
if (dictMode == ZSTD_dictMatchState) nbCompares = 0; /* break should also skip searching dms */
break; /* drop, to preserve bt consistency (miss a little bit of compression) */
}
}
} }
if (match[matchLength] < ip[matchLength]) {
/* match smaller than current */
@ -752,8 +751,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
if ( (matchLength > ZSTD_OPT_NUM)
| (ip+matchLength == iLimit) /* equal : no way to know if inf or sup */) {
break; /* drop, to guarantee consistency (miss a little bit of compression) */
}
}
} }
if (dictMatchIndex <= dmsBtLow) { break; } /* beyond tree size, stop the search */
if (match[matchLength] < ip[matchLength]) {
@ -763,9 +761,7 @@ U32 ZSTD_insertBtAndGetAllMatches (
/* match is larger than current */
commonLengthLarger = matchLength;
dictMatchIndex = nextPtr[0];
}
}
}
} } } /* if (dictMode == ZSTD_dictMatchState) */
assert(matchEndIdx > curr+8);
ms->nextToUpdate = matchEndIdx - 8; /* skip repetitive patterns */