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Merge branch 'dev' of github.com:facebook/zstd into dev

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Yann Collet
2018-11-13 15:56:36 -08:00
parent 092c4abd4c f28af025d9
commit 768a264200
5 changed files with 82 additions and 53 deletions
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lib/zstd.h
+38 -21
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@@ -996,6 +996,38 @@ typedef enum {
* Decoder cannot recognise automatically this format, requiring instructions. */
} ZSTD_format_e;
typedef enum {
/* Note: this enum and the behavior it controls are effectively internal
* implementation details of the compressor. They are expected to continue
* to evolve and should be considered only in the context of extremely
* advanced performance tuning.
*
* Zstd currently supports the use of a CDict in two ways:
*
* - The contents of the CDict can be copied into the working context. This
* means that the compression can search both the dictionary and input
* while operating on a single set of internal tables. This makes
* the compression faster per-byte of input. However, the initial copy of
* the CDict's tables incurs a fixed cost at the beginning of the
* compression. For small compressions (< 8 KB), that copy can dominate
* the cost of the compression.
*
* - The CDict's tables can be used in-place. In this model, compression is
* slower per input byte, because the compressor has to search two sets of
* tables. However, this model incurs no start-up cost (as long as the
* working context's tables can be reused). For small inputs, this can be
* faster than copying the CDict's tables.
*
* Zstd has a simple internal heuristic that selects which strategy to use
* at the beginning of a compression. However, if experimentation shows that
* Zstd is making poor choices, it is possible to override that choice with
* this enum.
*/
ZSTD_dictDefaultAttach = 0, /* Use the default heuristic. */
ZSTD_dictForceAttach = 1, /* Never copy the dictionary. */
ZSTD_dictForceCopy = 2, /* Always copy the dictionary. */
} ZSTD_dictAttachPref_e;
typedef enum {
/* compression format */
ZSTD_p_format = 10, /* See ZSTD_format_e enum definition.
@@ -1109,29 +1141,14 @@ typedef enum {
ZSTD_p_forceMaxWindow=1100, /* Force back-reference distances to remain < windowSize,
* even when referencing into Dictionary content (default:0) */
ZSTD_p_forceAttachDict, /* ZSTD supports usage of a CDict in-place
* (avoiding having to copy the compression tables
* from the CDict into the working context). Using
* a CDict in this way saves an initial setup step,
* but comes at the cost of more work per byte of
* input. ZSTD has a simple internal heuristic that
* guesses which strategy will be faster. You can
* use this flag to override that guess.
ZSTD_p_forceAttachDict, /* Controls whether the contents of a CDict are
* used in place, or whether they are copied into
* the working context.
*
* Note that the by-reference, in-place strategy is
* only used when reusing a compression context
* with compatible compression parameters. (If
* incompatible / uninitialized, the working
* context needs to be cleared anyways, which is
* about as expensive as overwriting it with the
* dictionary context, so there's no savings in
* using the CDict by-ref.)
*
* Values greater than 0 force attaching the dict.
* Values less than 0 force copying the dict.
* 0 selects the default heuristic-guided behavior.
* Accepts values from the ZSTD_dictAttachPref_e
* enum. See the comments on that enum for an
* explanation of the feature.
*/
} ZSTD_cParameter;