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Merge pull request #1152 from facebook/lowCompression

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btultra accepts blocks with poorer compression ratio
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Yann Collet 2018-05-25 17:46:11 -07:00 committed by GitHub
commit c6ccf435ae
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1 changed files with 11 additions and 3 deletions
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lib/compress/zstd_compress.c
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@ -1492,7 +1492,15 @@ static size_t ZSTD_compressRleLiteralsBlock (void* dst, size_t dstCapacity, cons
} }
static size_t ZSTD_minGain(size_t srcSize) { return (srcSize >> 6) + 2; } /* ZSTD_minGain() :
* minimum compression required
* to generate a compress block or a compressed literals section.
* note : use same formula for both situations */
static size_t ZSTD_minGain(size_t srcSize, ZSTD_strategy strat)
{
U32 const minlog = (strat==ZSTD_btultra) ? 7 : 6;
return (srcSize >> minlog) + 2;
}
static size_t ZSTD_compressLiterals (ZSTD_hufCTables_t const* prevHuf, static size_t ZSTD_compressLiterals (ZSTD_hufCTables_t const* prevHuf,
ZSTD_hufCTables_t* nextHuf, ZSTD_hufCTables_t* nextHuf,
@ -1501,7 +1509,7 @@ static size_t ZSTD_compressLiterals (ZSTD_hufCTables_t const* prevHuf,
const void* src, size_t srcSize, const void* src, size_t srcSize,
U32* workspace, const int bmi2) U32* workspace, const int bmi2)
{ {
size_t const minGain = ZSTD_minGain(srcSize); size_t const minGain = ZSTD_minGain(srcSize, strategy);
size_t const lhSize = 3 + (srcSize >= 1 KB) + (srcSize >= 16 KB); size_t const lhSize = 3 + (srcSize >= 1 KB) + (srcSize >= 16 KB);
BYTE* const ostart = (BYTE*)dst; BYTE* const ostart = (BYTE*)dst;
U32 singleStream = srcSize < 256; U32 singleStream = srcSize < 256;
@ -2162,7 +2170,7 @@ MEM_STATIC size_t ZSTD_compressSequences(seqStore_t* seqStorePtr,
if (ZSTD_isError(cSize)) return cSize; if (ZSTD_isError(cSize)) return cSize;
/* Check compressibility */ /* Check compressibility */
{ size_t const maxCSize = srcSize - ZSTD_minGain(srcSize); /* note : fixed formula; to be refined, depending on compression level, or strategy */ { size_t const maxCSize = srcSize - ZSTD_minGain(srcSize, cctxParams->cParams.strategy);
if (cSize >= maxCSize) return 0; /* block not compressed */ if (cSize >= maxCSize) return 0; /* block not compressed */
} }