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Introduce, implement, and call ZSTD_ldm_countBackwardsMatch_2segments()

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This commit is contained in:
senhuang42 2020-10-12 16:17:39 -04:00
parent 8c46c1d851
commit bf0d559449
1 changed files with 22 additions and 2 deletions
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24
lib/compress/zstd_ldm.c
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@ -154,6 +154,26 @@ static size_t ZSTD_ldm_countBackwardsMatch(
return matchLength;
}
/** ZSTD_ldm_countBackwardsMatch_2segments() :
* Returns the number of bytes that match backwards from pMatch,
* even with the backwards match spanning 2 different segments.
*
* On reaching `pMatchBase`, start counting from mEnd */
static size_t ZSTD_ldm_countBackwardsMatch_2segments(
const BYTE* pIn, const BYTE* pAnchor,
const BYTE* pMatch, const BYTE* pMatchBase, const BYTE* mEnd)
{
const BYTE* const vBegin = MAX(pIn - (pMatch - pMatchBase), pAnchor);
size_t const matchLength = ZSTD_ldm_countBackwardsMatch(pIn, vBegin, pMatch, pMatchBase);
if (pMatch - matchLength != pMatchBase) {
return matchLength;
}
DEBUGLOG(7, "ZSTD_ldm_countBackwardsMatch_2segments: found a 2-parts backwards match (current length==%zu)", matchLength);
DEBUGLOG(7, "distance from pMatch to start = %zi", pMatch - pMatchBase);
DEBUGLOG(7, "final backwards match length = %zu", matchLength + ZSTD_ldm_countBackwardsMatch(pIn - matchLength, pAnchor, mEnd, pMatchBase));
return matchLength + ZSTD_ldm_countBackwardsMatch(pIn - matchLength, pAnchor, mEnd, pMatchBase);
}
/** ZSTD_ldm_fillFastTables() :
*
* Fills the relevant tables for the ZSTD_fast and ZSTD_dfast strategies.
@ -329,8 +349,8 @@ static size_t ZSTD_ldm_generateSequences_internal(
continue;
}
curBackwardMatchLength =
ZSTD_ldm_countBackwardsMatch(ip, anchor, pMatch,
lowMatchPtr);
ZSTD_ldm_countBackwardsMatch_2segments(ip, anchor, pMatch,
lowMatchPtr, dictEnd);
curTotalMatchLength = curForwardMatchLength +
curBackwardMatchLength;
} else { /* !extDict */