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make it possible to express compression parameters in any order

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This commit is contained in:
Yann Collet
2018-03-19 14:41:23 -07:00
parent 9618c0c804
commit 6f4d0778a5
7 changed files with 110 additions and 150 deletions
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lib/zstd.h
+30 -31
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@@ -905,9 +905,8 @@ ZSTDLIB_API ZSTD_nextInputType_e ZSTD_nextInputType(ZSTD_DCtx* dctx);
* and then applied on all subsequent compression jobs.
* When no parameter is ever provided, CCtx is created with compression level ZSTD_CLEVEL_DEFAULT.
*
* This API is intended to replace all others experimental API.
* It can basically do all other use cases, and even new ones.
* It stands a reasonable chance to become "stable", after a good testing period.
* This API is intended to replace all others advanced / experimental API entry points.
* But it stands a reasonable chance to become "stable", after a reasonable testing period.
*/
/* note on naming convention :
@@ -924,12 +923,12 @@ ZSTDLIB_API ZSTD_nextInputType_e ZSTD_nextInputType(ZSTD_DCtx* dctx);
* All enum will be pinned to explicit values before reaching "stable API" status */
typedef enum {
/* Question : should we have a format ZSTD_f_auto ?
* For the time being, it would mean exactly the same as ZSTD_f_zstd1.
* But, in the future, should several formats be supported,
/* Opened question : should we have a format ZSTD_f_auto ?
* Today, it would mean exactly the same as ZSTD_f_zstd1.
* But, in the future, should several formats become supported,
* on the compression side, it would mean "default format".
* On the decompression side, it would mean "multi format",
* and ZSTD_f_zstd1 could be reserved to mean "accept *only* zstd frames".
* On the decompression side, it would mean "automatic format detection",
* so that ZSTD_f_zstd1 would mean "accept *only* zstd frames".
* Since meaning is a little different, another option could be to define different enums for compression and decompression.
* This question could be kept for later, when there are actually multiple formats to support,
* but there is also the question of pinning enum values, and pinning value `0` is especially important */
@@ -949,33 +948,34 @@ typedef enum {
* Default level is ZSTD_CLEVEL_DEFAULT==3.
* Special: value 0 means "do not change cLevel".
* Note 1 : it's possible to pass a negative compression level by casting it to unsigned type.
* Note 2 : setting compressionLevel automatically updates ZSTD_p_compressLiterals. */
* Note 2 : setting a level sets all default values of other compression parameters.
* Note 3 : setting compressionLevel automatically updates ZSTD_p_compressLiterals. */
ZSTD_p_windowLog, /* Maximum allowed back-reference distance, expressed as power of 2.
* Must be clamped between ZSTD_WINDOWLOG_MIN and ZSTD_WINDOWLOG_MAX.
* Special: value 0 means "do not change windowLog".
* Special: value 0 means "use default windowLog".
* Note: Using a window size greater than ZSTD_MAXWINDOWSIZE_DEFAULT (default: 2^27)
* requires setting the maximum window size at least as large during decompression. */
* requires explicitly allowing such window size during decompression stage. */
ZSTD_p_hashLog, /* Size of the probe table, as a power of 2.
* Resulting table size is (1 << (hashLog+2)).
* Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX.
* Larger tables improve compression ratio of strategies <= dFast,
* and improve speed of strategies > dFast.
* Special: value 0 means "do not change hashLog". */
* Special: value 0 means "use default hashLog". */
ZSTD_p_chainLog, /* Size of the full-search table, as a power of 2.
* Resulting table size is (1 << (chainLog+2)).
* Larger tables result in better and slower compression.
* This parameter is useless when using "fast" strategy.
* Special: value 0 means "do not change chainLog". */
* Special: value 0 means "use default chainLog". */
ZSTD_p_searchLog, /* Number of search attempts, as a power of 2.
* More attempts result in better and slower compression.
* This parameter is useless when using "fast" and "dFast" strategies.
* Special: value 0 means "do not change searchLog". */
* Special: value 0 means "use default searchLog". */
ZSTD_p_minMatch, /* Minimum size of searched matches (note : repCode matches can be smaller).
* Larger values make faster compression and decompression, but decrease ratio.
* Must be clamped between ZSTD_SEARCHLENGTH_MIN and ZSTD_SEARCHLENGTH_MAX.
* Note that currently, for all strategies < btopt, effective minimum is 4.
* Note that currently, for all strategies > fast, effective maximum is 6.
* Special: value 0 means "do not change minMatchLength". */
* , for all strategies > fast, effective maximum is 6.
* Special: value 0 means "use default minMatchLength". */
ZSTD_p_targetLength, /* Impact of this field depends on strategy.
* For strategies btopt & btultra:
* Length of Match considered "good enough" to stop search.
@@ -983,27 +983,26 @@ typedef enum {
* For strategy fast:
* Distance between match sampling.
* Larger values make compression faster, and weaker.
* Special: value 0 means "do not change targetLength". */
* Special: value 0 means "use default targetLength". */
ZSTD_p_compressionStrategy, /* See ZSTD_strategy enum definition.
* Cast selected strategy as unsigned for ZSTD_CCtx_setParameter() compatibility.
* The higher the value of selected strategy, the more complex it is,
* resulting in stronger and slower compression.
* Special: value 0 means "do not change strategy". */
* Special: value 0 means "use default strategy". */
ZSTD_p_enableLongDistanceMatching=160, /* Enable long distance matching.
* This parameter is designed to improve compression ratio
* for large inputs, thanks to long distance matches.
* for large inputs, by finding large matches at long distance.
* It increases memory usage and window size.
* Note: setting this parameter sets ZSTD_p_windowLog.
* Setting compression level after LDM overrides the window log,
* though LDM will remain enabled until explicitly disabled. */
* Note: enabling this parameter increases ZSTD_p_windowLog to 128 MB
* except when expressly set to a different value. */
ZSTD_p_ldmHashLog, /* Size of the table for long distance matching, as a power of 2.
* Larger values increase memory usage and compression ratio, but decrease
* compression speed.
* Larger values increase memory usage and compression ratio,
* but decrease compression speed.
* Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX
* (default: windowlog - 7).
* default: windowlog - 7.
* Special: value 0 means "automatically determine hashlog". */
ZSTD_p_ldmMinMatch, /* Minimum size of searched matches for long distance matcher.
ZSTD_p_ldmMinMatch, /* Minimum match size for long distance matcher.
* Larger/too small values usually decrease compression ratio.
* Must be clamped between ZSTD_LDM_MINMATCH_MIN and ZSTD_LDM_MINMATCH_MAX.
* Special: value 0 means "use default value" (default: 64). */
@@ -1012,11 +1011,10 @@ typedef enum {
* The maximum value is ZSTD_LDM_BUCKETSIZELOG_MAX .
* Special: value 0 means "use default value" (default: 3). */
ZSTD_p_ldmHashEveryLog, /* Frequency of inserting/looking up entries in the LDM hash table.
* The default is MAX(0, (windowLog - ldmHashLog)) to
* optimize hash table usage.
* Must be clamped between 0 and (ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN).
* Default is MAX(0, (windowLog - ldmHashLog)), optimizing hash table usage.
* Larger values improve compression speed.
* Deviating far from default value will likely result in a compression ratio decrease.
* Must be clamped between 0 and (ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN).
* Special: value 0 means "automatically determine hashEveryLog". */
/* frame parameters */
@@ -1044,7 +1042,9 @@ typedef enum {
ZSTD_p_overlapSizeLog, /* Size of previous input reloaded at the beginning of each job.
* 0 => no overlap, 6(default) => use 1/8th of windowSize, >=9 => use full windowSize */
/* advanced parameters - may not remain available after API update */
/* =================================================================== */
/* experimental parameters - no stability guaranteed */
/* =================================================================== */
ZSTD_p_compressLiterals=1000, /* control huffman compression of literals (enabled) by default.
* disabling it improves speed and decreases compression ratio by a large amount.
@@ -1055,7 +1055,6 @@ typedef enum {
ZSTD_p_forceMaxWindow=1100, /* Force back-reference distances to remain < windowSize,
* even when referencing into Dictionary content (default:0) */
} ZSTD_cParameter;