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[docs] Clarify dictionary loading documentation #3381

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Dec 20, 2022
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[docs] Clarify dictionary loading documentation #3381

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18 changes: 10 additions & 8 deletions lib/zstd.h
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Original file line number Diff line number Diff line change
Expand Up @@ -990,8 +990,9 @@ ZSTDLIB_API unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
* @result : 0, or an error code (which can be tested with ZSTD_isError()).
* Special: Loading a NULL (or 0-size) dictionary invalidates previous dictionary,
* meaning "return to no-dictionary mode".
* Note 1 : Dictionary is sticky, it will be used for all future compressed frames.
* To return to "no-dictionary" situation, load a NULL dictionary (or reset parameters).
* Note 1 : Dictionary is sticky, it will be used for all future compressed frames,
* until parameters are reset, a new dictionary is loaded, or the dictionary
* is explicitly invalidated by loading a NULL dictionary.
* Note 2 : Loading a dictionary involves building tables.
* It's also a CPU consuming operation, with non-negligible impact on latency.
* Tables are dependent on compression parameters, and for this reason,
Expand All @@ -1004,7 +1005,7 @@ ZSTDLIB_API unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
ZSTDLIB_API size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize);

/*! ZSTD_CCtx_refCDict() : Requires v1.4.0+
* Reference a prepared dictionary, to be used for all next compressed frames.
* Reference a prepared dictionary, to be used for all future compressed frames.
* Note that compression parameters are enforced from within CDict,
* and supersede any compression parameter previously set within CCtx.
* The parameters ignored are labelled as "superseded-by-cdict" in the ZSTD_cParameter enum docs.
Expand Down Expand Up @@ -1039,9 +1040,9 @@ ZSTDLIB_API size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx,
const void* prefix, size_t prefixSize);

/*! ZSTD_DCtx_loadDictionary() : Requires v1.4.0+
* Create an internal DDict from dict buffer,
* to be used to decompress next frames.
* The dictionary remains valid for all future frames, until explicitly invalidated.
* Create an internal DDict from dict buffer, to be used to decompress all future frames.
* The dictionary remains valid for all future frames, until explicitly invalidated, or
* a new dictionary is loaded.
* @result : 0, or an error code (which can be tested with ZSTD_isError()).
* Special : Adding a NULL (or 0-size) dictionary invalidates any previous dictionary,
* meaning "return to no-dictionary mode".
Expand All @@ -1065,9 +1066,10 @@ ZSTDLIB_API size_t ZSTD_DCtx_loadDictionary(ZSTD_DCtx* dctx, const void* dict, s
* The memory for the table is allocated on the first call to refDDict, and can be
* freed with ZSTD_freeDCtx().
*
* If called with ZSTD_d_refMultipleDDicts disabled (the default), only one dictionary
* will be managed, and referencing a dictionary effectively "discards" any previous one.
*
* @result : 0, or an error code (which can be tested with ZSTD_isError()).
* Note 1 : Currently, only one dictionary can be managed.
* Referencing a new dictionary effectively "discards" any previous one.
* Special: referencing a NULL DDict means "return to no-dictionary mode".
* Note 2 : DDict is just referenced, its lifetime must outlive its usage from DCtx.
*/
Expand Down