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Merge pull request #1624 from facebook/smallwlog

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Improves compression ratio for small windowLog
This commit is contained in:
Yann Collet
2019-06-14 17:28:21 -07:00
committed by GitHub
parent 018df9c9b1 80d6ccea79
commit 9af909bf35
6 changed files with 115 additions and 50 deletions
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6
lib/compress/zstd_opt.c
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@ -547,6 +547,7 @@ 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;
@ -562,8 +563,9 @@ U32 ZSTD_insertBtAndGetAllMatches (
U32 const dictLimit = ms->window.dictLimit;
const BYTE* const dictEnd = dictBase + dictLimit;
const BYTE* const prefixStart = base + dictLimit;
U32 const btLow = btMask >= current ? 0 : current - btMask;
U32 const windowLow = ms->window.lowLimit;
U32 const btLow = (btMask >= current) ? 0 : current - btMask;
U32 const windowValid = ms->window.lowLimit;
U32 const windowLow = ((current - windowValid) > maxDistance) ? current - maxDistance : windowValid;
U32 const matchLow = windowLow ? windowLow : 1;
U32* smallerPtr = bt + 2*(current&btMask);
U32* largerPtr = bt + 2*(current&btMask) + 1;