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Always check Huffman tables for ZSTD_lazy+

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The compressor always reuses the existing Huffman table if the literals
size is at most 1 KiB. If the compression strategy is `ZSTD_lazy` or
stronger always check to see if reusing the previous table or creating
a new table is better.

This doesn't yet weigh in decompression speed. I don't want to add any
heuristics there until I have real data to work with to ensure that the
heuristic works for at least one use case, preferably more.
This commit is contained in:
Nick Terrell
2017-03-03 16:49:38 -08:00
parent f44b55c18d
commit 54c4babd8f
3 changed files with 19 additions and 15 deletions
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lib/common/huf.h
+6 -4
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@@ -180,8 +180,9 @@ typedef enum {
/** HUF_compress4X_repeat() :
* Same as HUF_compress4X_wksp(), but considers using hufTable if *repeat != HUF_repeat_none.
* If it uses hufTable it does not modify hufTable or repeat.
* If it doesn't, it sets *repeat = HUF_repeat_none, and it sets hufTable to the table used. */
size_t HUF_compress4X_repeat(void* dst, size_t dstSize, const void* src, size_t srcSize, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize, HUF_CElt* hufTable, HUF_repeat* repeat); /**< `workSpace` must be a table of at least HUF_WORKSPACE_SIZE_U32 unsigned */
* If it doesn't, it sets *repeat = HUF_repeat_none, and it sets hufTable to the table used.
* If preferRepeat then the old table will always be used if valid. */
size_t HUF_compress4X_repeat(void* dst, size_t dstSize, const void* src, size_t srcSize, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize, HUF_CElt* hufTable, HUF_repeat* repeat, int preferRepeat); /**< `workSpace` must be a table of at least HUF_WORKSPACE_SIZE_U32 unsigned */
/** HUF_buildCTable_wksp() :
* Same as HUF_buildCTable(), but using externally allocated scratch buffer.
@@ -233,8 +234,9 @@ size_t HUF_compress1X_usingCTable(void* dst, size_t dstSize, const void* src, si
/** HUF_compress1X_repeat() :
* Same as HUF_compress1X_wksp(), but considers using hufTable if *repeat != HUF_repeat_none.
* If it uses hufTable it does not modify hufTable or repeat.
* If it doesn't, it sets *repeat = HUF_repeat_none, and it sets hufTable to the table used. */
size_t HUF_compress1X_repeat(void* dst, size_t dstSize, const void* src, size_t srcSize, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize, HUF_CElt* hufTable, HUF_repeat* repeat); /**< `workSpace` must be a table of at least HUF_WORKSPACE_SIZE_U32 unsigned */
* If it doesn't, it sets *repeat = HUF_repeat_none, and it sets hufTable to the table used.
* If preferRepeat then the old table will always be used if valid. */
size_t HUF_compress1X_repeat(void* dst, size_t dstSize, const void* src, size_t srcSize, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize, HUF_CElt* hufTable, HUF_repeat* repeat, int preferRepeat); /**< `workSpace` must be a table of at least HUF_WORKSPACE_SIZE_U32 unsigned */
size_t HUF_decompress1X2 (void* dst, size_t dstSize, const void* cSrc, size_t cSrcSize); /* single-symbol decoder */
size_t HUF_decompress1X4 (void* dst, size_t dstSize, const void* cSrc, size_t cSrcSize); /* double-symbol decoder */