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updated documentation of *refPrefix()

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indicating the equivalence with `diff` operation.
This commit is contained in:
Yann Collet
2018-09-18 13:07:08 -07:00
parent f884e9dd8e
commit 005f000aed
2 changed files with 22 additions and 8 deletions
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lib/zstd.h
+11 -4
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@@ -1164,16 +1164,21 @@ ZSTDLIB_API size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict);
/*! ZSTD_CCtx_refPrefix() :
* Reference a prefix (single-usage dictionary) for next compression job.
* Decompression need same prefix to properly regenerate data.
* Prefix is **only used once**. Tables are discarded at end of compression job (ZSTD_e_end).
* Decompression will need same prefix to properly regenerate data.
* Compressing with a prefix is similar in outcome as performing a diff and compressing it,
* but performs much faster, especially during decompression (compression speed is tunable with compression level).
* Note that prefix is **only used once**. Tables are discarded at end of compression job (ZSTD_e_end).
* @result : 0, or an error code (which can be tested with ZSTD_isError()).
* Special: Adding any prefix (including NULL) invalidates any previous prefix or dictionary
* Note 1 : Prefix buffer is referenced. It **must** outlive compression job.
* Its contain must remain unmodified up to end of compression (ZSTD_e_end).
* Note 2 : Referencing a prefix involves building tables, which are dependent on compression parameters.
* Note 2 : If the intention is to diff some large src data blob with some prior version of itself,
* ensure that the window size is large enough to contain the entire source.
* See ZSTD_p_windowLog.
* Note 3 : Referencing a prefix involves building tables, which are dependent on compression parameters.
* It's a CPU consuming operation, with non-negligible impact on latency.
* If there is a need to use same prefix multiple times, consider loadDictionary instead.
* Note 3 : By default, the prefix is treated as raw content (ZSTD_dm_rawContent).
* Note 4 : By default, the prefix is treated as raw content (ZSTD_dm_rawContent).
* Use ZSTD_CCtx_refPrefix_advanced() to alter dictMode. */
ZSTDLIB_API size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx,
const void* prefix, size_t prefixSize);
@@ -1356,6 +1361,8 @@ ZSTDLIB_API size_t ZSTD_DCtx_refDDict(ZSTD_DCtx* dctx, const ZSTD_DDict* ddict);
/*! ZSTD_DCtx_refPrefix() :
* Reference a prefix (single-usage dictionary) for next compression job.
* This is the reverse operation of ZSTD_CCtx_refPrefix(),
* and must use the same prefix as the one used during compression.
* Prefix is **only used once**. Reference is discarded at end of frame.
* End of frame is reached when ZSTD_DCtx_decompress_generic() returns 0.
* @result : 0, or an error code (which can be tested with ZSTD_isError()).