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Merge pull request #2376 from senhuang42/clarify_sequence_extraction_api

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Refine external ZSTD_Sequence API
This commit is contained in:
sen
2020-10-30 15:47:25 -04:00
committed by GitHub
parent ff93440fc6 f0da97642a
commit c37c714ef1
4 changed files with 90 additions and 50 deletions
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lib/zstd.h
+36 -16
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@@ -1116,21 +1116,39 @@ ZSTDLIB_API size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
typedef struct ZSTD_CCtx_params_s ZSTD_CCtx_params;
typedef struct {
unsigned int matchPos; /* Match pos in dst */
/* If seqDef.offset > 3, then this is seqDef.offset - 3
* If seqDef.offset < 3, then this is the corresponding repeat offset
* But if seqDef.offset < 3 and litLength == 0, this is the
* repeat offset before the corresponding repeat offset
* And if seqDef.offset == 3 and litLength == 0, this is the
* most recent repeat offset - 1
*/
unsigned int offset;
unsigned int litLength; /* Literal length */
unsigned int matchLength; /* Match length */
/* 0 when seq not rep and seqDef.offset otherwise
* when litLength == 0 this will be <= 4, otherwise <= 3 like normal
*/
unsigned int rep;
unsigned int offset; /* The offset of the match. (NOT the same as the offset code)
* If offset == 0 and matchLength == 0, this sequence represents the last
* literals in the block of litLength size.
*/
unsigned int litLength; /* Literal length of the sequence. */
unsigned int matchLength; /* Match length of the sequence. */
/* Note: Users of this API may provide a sequence with matchLength == litLength == offset == 0.
* In this case, we will treat the sequence as a marker for a block boundary.
*/
unsigned int rep; /* Represents which repeat offset is represented by the field 'offset'.
* Ranges from [0, 3].
*
* Repeat offsets are essentially previous offsets from previous sequences sorted in
* recency order. For more detail, see doc/zstd_compression_format.md
*
* If rep == 0, then 'offset' does not contain a repeat offset.
* If rep > 0:
* If litLength != 0:
* rep == 1 --> offset == repeat_offset_1
* rep == 2 --> offset == repeat_offset_2
* rep == 3 --> offset == repeat_offset_3
* If litLength == 0:
* rep == 1 --> offset == repeat_offset_2
* rep == 2 --> offset == repeat_offset_3
* rep == 3 --> offset == repeat_offset_1 - 1
*
* Note: This field is optional. ZSTD_getSequences() will calculate the value of
* 'rep', but repeat offsets do not necessarily need to be calculated from an external
* sequence provider's perspective.
*/
} ZSTD_Sequence;
typedef struct {
@@ -1276,7 +1294,9 @@ ZSTDLIB_API unsigned long long ZSTD_decompressBound(const void* src, size_t srcS
ZSTDLIB_API size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize);
/*! ZSTD_getSequences() :
* Extract sequences from the sequence store
* Extract sequences from the sequence store.
* Each block will end with a dummy sequence with offset == 0, matchLength == 0, and litLength == length of last literals.
*
* zc can be used to insert custom compression params.
* This function invokes ZSTD_compress2
* @return : number of sequences extracted