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- <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
- <title>zstd 1.4.9 Manual</title>
- </head>
- <body>
- <h1>zstd 1.4.9 Manual</h1>
- <hr>
- <a name="Contents"></a><h2>Contents</h2>
- <ol>
- <li><a href="#Chapter1">Introduction</a></li>
- <li><a href="#Chapter2">Version</a></li>
- <li><a href="#Chapter3">Simple API</a></li>
- <li><a href="#Chapter4">Explicit context</a></li>
- <li><a href="#Chapter5">Advanced compression API</a></li>
- <li><a href="#Chapter6">Advanced decompression API</a></li>
- <li><a href="#Chapter7">Streaming</a></li>
- <li><a href="#Chapter8">Streaming compression - HowTo</a></li>
- <li><a href="#Chapter9">Streaming decompression - HowTo</a></li>
- <li><a href="#Chapter10">Simple dictionary API</a></li>
- <li><a href="#Chapter11">Bulk processing dictionary API</a></li>
- <li><a href="#Chapter12">Dictionary helper functions</a></li>
- <li><a href="#Chapter13">Advanced dictionary and prefix API</a></li>
- <li><a href="#Chapter14">experimental API (static linking only)</a></li>
- <li><a href="#Chapter15">Frame size functions</a></li>
- <li><a href="#Chapter16">Memory management</a></li>
- <li><a href="#Chapter17">Advanced compression functions</a></li>
- <li><a href="#Chapter18">Advanced decompression functions</a></li>
- <li><a href="#Chapter19">Advanced streaming functions</a></li>
- <li><a href="#Chapter20">Buffer-less and synchronous inner streaming functions</a></li>
- <li><a href="#Chapter21">Buffer-less streaming compression (synchronous mode)</a></li>
- <li><a href="#Chapter22">Buffer-less streaming decompression (synchronous mode)</a></li>
- <li><a href="#Chapter23">Block level API</a></li>
- </ol>
- <hr>
- <a name="Chapter1"></a><h2>Introduction</h2><pre>
- zstd, short for Zstandard, is a fast lossless compression algorithm, targeting
- real-time compression scenarios at zlib-level and better compression ratios.
- The zstd compression library provides in-memory compression and decompression
- functions.
- The library supports regular compression levels from 1 up to ZSTD_maxCLevel(),
- which is currently 22. Levels >= 20, labeled `--ultra`, should be used with
- caution, as they require more memory. The library also offers negative
- compression levels, which extend the range of speed vs. ratio preferences.
- The lower the level, the faster the speed (at the cost of compression).
- Compression can be done in:
- - a single step (described as Simple API)
- - a single step, reusing a context (described as Explicit context)
- - unbounded multiple steps (described as Streaming compression)
- The compression ratio achievable on small data can be highly improved using
- a dictionary. Dictionary compression can be performed in:
- - a single step (described as Simple dictionary API)
- - a single step, reusing a dictionary (described as Bulk-processing
- dictionary API)
- Advanced experimental functions can be accessed using
- `#define ZSTD_STATIC_LINKING_ONLY` before including zstd.h.
- Advanced experimental APIs should never be used with a dynamically-linked
- library. They are not "stable"; their definitions or signatures may change in
- the future. Only static linking is allowed.
- <BR></pre>
- <a name="Chapter2"></a><h2>Version</h2><pre></pre>
- <pre><b>unsigned ZSTD_versionNumber(void);
- </b><p> Return runtime library version, the value is (MAJOR*100*100 + MINOR*100 + RELEASE).
- </p></pre><BR>
- <pre><b>const char* ZSTD_versionString(void);
- </b><p> Return runtime library version, like "1.4.5". Requires v1.3.0+.
- </p></pre><BR>
- <a name="Chapter3"></a><h2>Simple API</h2><pre></pre>
- <pre><b>size_t ZSTD_compress( void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- int compressionLevel);
- </b><p> Compresses `src` content as a single zstd compressed frame into already allocated `dst`.
- Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
- @return : compressed size written into `dst` (<= `dstCapacity),
- or an error code if it fails (which can be tested using ZSTD_isError()).
- </p></pre><BR>
- <pre><b>size_t ZSTD_decompress( void* dst, size_t dstCapacity,
- const void* src, size_t compressedSize);
- </b><p> `compressedSize` : must be the _exact_ size of some number of compressed and/or skippable frames.
- `dstCapacity` is an upper bound of originalSize to regenerate.
- If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data.
- @return : the number of bytes decompressed into `dst` (<= `dstCapacity`),
- or an errorCode if it fails (which can be tested using ZSTD_isError()).
- </p></pre><BR>
- <pre><b>#define ZSTD_CONTENTSIZE_UNKNOWN (0ULL - 1)
- #define ZSTD_CONTENTSIZE_ERROR (0ULL - 2)
- unsigned long long ZSTD_getFrameContentSize(const void *src, size_t srcSize);
- </b><p> `src` should point to the start of a ZSTD encoded frame.
- `srcSize` must be at least as large as the frame header.
- hint : any size >= `ZSTD_frameHeaderSize_max` is large enough.
- @return : - decompressed size of `src` frame content, if known
- - ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined
- - ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small)
- note 1 : a 0 return value means the frame is valid but "empty".
- note 2 : decompressed size is an optional field, it may not be present, typically in streaming mode.
- When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size.
- In which case, it's necessary to use streaming mode to decompress data.
- Optionally, application can rely on some implicit limit,
- as ZSTD_decompress() only needs an upper bound of decompressed size.
- (For example, data could be necessarily cut into blocks <= 16 KB).
- note 3 : decompressed size is always present when compression is completed using single-pass functions,
- such as ZSTD_compress(), ZSTD_compressCCtx() ZSTD_compress_usingDict() or ZSTD_compress_usingCDict().
- note 4 : decompressed size can be very large (64-bits value),
- potentially larger than what local system can handle as a single memory segment.
- In which case, it's necessary to use streaming mode to decompress data.
- note 5 : If source is untrusted, decompressed size could be wrong or intentionally modified.
- Always ensure return value fits within application's authorized limits.
- Each application can set its own limits.
- note 6 : This function replaces ZSTD_getDecompressedSize()
- </p></pre><BR>
- <pre><b>unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
- </b><p> NOTE: This function is now obsolete, in favor of ZSTD_getFrameContentSize().
- Both functions work the same way, but ZSTD_getDecompressedSize() blends
- "empty", "unknown" and "error" results to the same return value (0),
- while ZSTD_getFrameContentSize() gives them separate return values.
- @return : decompressed size of `src` frame content _if known and not empty_, 0 otherwise.
- </p></pre><BR>
- <pre><b>size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize);
- </b><p> `src` should point to the start of a ZSTD frame or skippable frame.
- `srcSize` must be >= first frame size
- @return : the compressed size of the first frame starting at `src`,
- suitable to pass as `srcSize` to `ZSTD_decompress` or similar,
- or an error code if input is invalid
- </p></pre><BR>
- <h3>Helper functions</h3><pre></pre><b><pre>#define ZSTD_COMPRESSBOUND(srcSize) ((srcSize) + ((srcSize)>>8) + (((srcSize) < (128<<10)) ? (((128<<10) - (srcSize)) >> 11) </b>/* margin, from 64 to 0 */ : 0)) /* this formula ensures that bound(A) + bound(B) <= bound(A+B) as long as A and B >= 128 KB */<b>
- size_t ZSTD_compressBound(size_t srcSize); </b>/*!< maximum compressed size in worst case single-pass scenario */<b>
- unsigned ZSTD_isError(size_t code); </b>/*!< tells if a `size_t` function result is an error code */<b>
- const char* ZSTD_getErrorName(size_t code); </b>/*!< provides readable string from an error code */<b>
- int ZSTD_minCLevel(void); </b>/*!< minimum negative compression level allowed */<b>
- int ZSTD_maxCLevel(void); </b>/*!< maximum compression level available */<b>
- </pre></b><BR>
- <a name="Chapter4"></a><h2>Explicit context</h2><pre></pre>
- <h3>Compression context</h3><pre> When compressing many times,
- it is recommended to allocate a context just once,
- and re-use it for each successive compression operation.
- This will make workload friendlier for system's memory.
- Note : re-using context is just a speed / resource optimization.
- It doesn't change the compression ratio, which remains identical.
- Note 2 : In multi-threaded environments,
- use one different context per thread for parallel execution.
-
- </pre><b><pre>typedef struct ZSTD_CCtx_s ZSTD_CCtx;
- ZSTD_CCtx* ZSTD_createCCtx(void);
- size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx);
- </pre></b><BR>
- <pre><b>size_t ZSTD_compressCCtx(ZSTD_CCtx* cctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- int compressionLevel);
- </b><p> Same as ZSTD_compress(), using an explicit ZSTD_CCtx.
- Important : in order to behave similarly to `ZSTD_compress()`,
- this function compresses at requested compression level,
- __ignoring any other parameter__ .
- If any advanced parameter was set using the advanced API,
- they will all be reset. Only `compressionLevel` remains.
-
- </p></pre><BR>
- <h3>Decompression context</h3><pre> When decompressing many times,
- it is recommended to allocate a context only once,
- and re-use it for each successive compression operation.
- This will make workload friendlier for system's memory.
- Use one context per thread for parallel execution.
- </pre><b><pre>typedef struct ZSTD_DCtx_s ZSTD_DCtx;
- ZSTD_DCtx* ZSTD_createDCtx(void);
- size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx);
- </pre></b><BR>
- <pre><b>size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize);
- </b><p> Same as ZSTD_decompress(),
- requires an allocated ZSTD_DCtx.
- Compatible with sticky parameters.
-
- </p></pre><BR>
- <a name="Chapter5"></a><h2>Advanced compression API</h2><pre></pre>
- <pre><b>typedef enum { ZSTD_fast=1,
- ZSTD_dfast=2,
- ZSTD_greedy=3,
- ZSTD_lazy=4,
- ZSTD_lazy2=5,
- ZSTD_btlazy2=6,
- ZSTD_btopt=7,
- ZSTD_btultra=8,
- ZSTD_btultra2=9
- </b>/* note : new strategies _might_ be added in the future.<b>
- Only the order (from fast to strong) is guaranteed */
- } ZSTD_strategy;
- </b></pre><BR>
- <pre><b>typedef enum {
- </b>/* compression parameters<b>
- * Note: When compressing with a ZSTD_CDict these parameters are superseded
- * by the parameters used to construct the ZSTD_CDict.
- * See ZSTD_CCtx_refCDict() for more info (superseded-by-cdict). */
- ZSTD_c_compressionLevel=100, </b>/* Set compression parameters according to pre-defined cLevel table.<b>
- * Note that exact compression parameters are dynamically determined,
- * depending on both compression level and srcSize (when known).
- * Default level is ZSTD_CLEVEL_DEFAULT==3.
- * Special: value 0 means default, which is controlled by ZSTD_CLEVEL_DEFAULT.
- * Note 1 : it's possible to pass a negative compression level.
- * Note 2 : setting a level does not automatically set all other compression parameters
- * to default. Setting this will however eventually dynamically impact the compression
- * parameters which have not been manually set. The manually set
- * ones will 'stick'. */
- </b>/* Advanced compression parameters :<b>
- * It's possible to pin down compression parameters to some specific values.
- * In which case, these values are no longer dynamically selected by the compressor */
- ZSTD_c_windowLog=101, </b>/* Maximum allowed back-reference distance, expressed as power of 2.<b>
- * This will set a memory budget for streaming decompression,
- * with larger values requiring more memory
- * and typically compressing more.
- * Must be clamped between ZSTD_WINDOWLOG_MIN and ZSTD_WINDOWLOG_MAX.
- * Special: value 0 means "use default windowLog".
- * Note: Using a windowLog greater than ZSTD_WINDOWLOG_LIMIT_DEFAULT
- * requires explicitly allowing such size at streaming decompression stage. */
- ZSTD_c_hashLog=102, </b>/* Size of the initial probe table, as a power of 2.<b>
- * Resulting memory usage 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 "use default hashLog". */
- ZSTD_c_chainLog=103, </b>/* Size of the multi-probe search table, as a power of 2.<b>
- * Resulting memory usage is (1 << (chainLog+2)).
- * Must be clamped between ZSTD_CHAINLOG_MIN and ZSTD_CHAINLOG_MAX.
- * Larger tables result in better and slower compression.
- * This parameter is useless for "fast" strategy.
- * It's still useful when using "dfast" strategy,
- * in which case it defines a secondary probe table.
- * Special: value 0 means "use default chainLog". */
- ZSTD_c_searchLog=104, </b>/* Number of search attempts, as a power of 2.<b>
- * More attempts result in better and slower compression.
- * This parameter is useless for "fast" and "dFast" strategies.
- * Special: value 0 means "use default searchLog". */
- ZSTD_c_minMatch=105, </b>/* Minimum size of searched matches.<b>
- * Note that Zstandard can still find matches of smaller size,
- * it just tweaks its search algorithm to look for this size and larger.
- * Larger values increase compression and decompression speed, but decrease ratio.
- * Must be clamped between ZSTD_MINMATCH_MIN and ZSTD_MINMATCH_MAX.
- * Note that currently, for all strategies < btopt, effective minimum is 4.
- * , for all strategies > fast, effective maximum is 6.
- * Special: value 0 means "use default minMatchLength". */
- ZSTD_c_targetLength=106, </b>/* Impact of this field depends on strategy.<b>
- * For strategies btopt, btultra & btultra2:
- * Length of Match considered "good enough" to stop search.
- * Larger values make compression stronger, and slower.
- * For strategy fast:
- * Distance between match sampling.
- * Larger values make compression faster, and weaker.
- * Special: value 0 means "use default targetLength". */
- ZSTD_c_strategy=107, </b>/* See ZSTD_strategy enum definition.<b>
- * The higher the value of selected strategy, the more complex it is,
- * resulting in stronger and slower compression.
- * Special: value 0 means "use default strategy". */
- </b>/* LDM mode parameters */<b>
- ZSTD_c_enableLongDistanceMatching=160, </b>/* Enable long distance matching.<b>
- * This parameter is designed to improve compression ratio
- * for large inputs, by finding large matches at long distance.
- * It increases memory usage and window size.
- * Note: enabling this parameter increases default ZSTD_c_windowLog to 128 MB
- * except when expressly set to a different value.
- * Note: will be enabled by default if ZSTD_c_windowLog >= 128 MB and
- * compression strategy >= ZSTD_btopt (== compression level 16+) */
- ZSTD_c_ldmHashLog=161, </b>/* Size of the table for long distance matching, as a power of 2.<b>
- * 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.
- * Special: value 0 means "automatically determine hashlog". */
- ZSTD_c_ldmMinMatch=162, </b>/* Minimum match size for long distance matcher.<b>
- * 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). */
- ZSTD_c_ldmBucketSizeLog=163, </b>/* Log size of each bucket in the LDM hash table for collision resolution.<b>
- * Larger values improve collision resolution but decrease compression speed.
- * The maximum value is ZSTD_LDM_BUCKETSIZELOG_MAX.
- * Special: value 0 means "use default value" (default: 3). */
- ZSTD_c_ldmHashRateLog=164, </b>/* Frequency of inserting/looking up entries into the LDM hash table.<b>
- * 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.
- * Special: value 0 means "automatically determine hashRateLog". */
- </b>/* frame parameters */<b>
- ZSTD_c_contentSizeFlag=200, </b>/* Content size will be written into frame header _whenever known_ (default:1)<b>
- * Content size must be known at the beginning of compression.
- * This is automatically the case when using ZSTD_compress2(),
- * For streaming scenarios, content size must be provided with ZSTD_CCtx_setPledgedSrcSize() */
- ZSTD_c_checksumFlag=201, </b>/* A 32-bits checksum of content is written at end of frame (default:0) */<b>
- ZSTD_c_dictIDFlag=202, </b>/* When applicable, dictionary's ID is written into frame header (default:1) */<b>
- </b>/* multi-threading parameters */<b>
- </b>/* These parameters are only active if multi-threading is enabled (compiled with build macro ZSTD_MULTITHREAD).<b>
- * Otherwise, trying to set any other value than default (0) will be a no-op and return an error.
- * In a situation where it's unknown if the linked library supports multi-threading or not,
- * setting ZSTD_c_nbWorkers to any value >= 1 and consulting the return value provides a quick way to check this property.
- */
- ZSTD_c_nbWorkers=400, </b>/* Select how many threads will be spawned to compress in parallel.<b>
- * When nbWorkers >= 1, triggers asynchronous mode when invoking ZSTD_compressStream*() :
- * ZSTD_compressStream*() consumes input and flush output if possible, but immediately gives back control to caller,
- * while compression is performed in parallel, within worker thread(s).
- * (note : a strong exception to this rule is when first invocation of ZSTD_compressStream2() sets ZSTD_e_end :
- * in which case, ZSTD_compressStream2() delegates to ZSTD_compress2(), which is always a blocking call).
- * More workers improve speed, but also increase memory usage.
- * Default value is `0`, aka "single-threaded mode" : no worker is spawned,
- * compression is performed inside Caller's thread, and all invocations are blocking */
- ZSTD_c_jobSize=401, </b>/* Size of a compression job. This value is enforced only when nbWorkers >= 1.<b>
- * Each compression job is completed in parallel, so this value can indirectly impact the nb of active threads.
- * 0 means default, which is dynamically determined based on compression parameters.
- * Job size must be a minimum of overlap size, or 1 MB, whichever is largest.
- * The minimum size is automatically and transparently enforced. */
- ZSTD_c_overlapLog=402, </b>/* Control the overlap size, as a fraction of window size.<b>
- * The overlap size is an amount of data reloaded from previous job at the beginning of a new job.
- * It helps preserve compression ratio, while each job is compressed in parallel.
- * This value is enforced only when nbWorkers >= 1.
- * Larger values increase compression ratio, but decrease speed.
- * Possible values range from 0 to 9 :
- * - 0 means "default" : value will be determined by the library, depending on strategy
- * - 1 means "no overlap"
- * - 9 means "full overlap", using a full window size.
- * Each intermediate rank increases/decreases load size by a factor 2 :
- * 9: full window; 8: w/2; 7: w/4; 6: w/8; 5:w/16; 4: w/32; 3:w/64; 2:w/128; 1:no overlap; 0:default
- * default value varies between 6 and 9, depending on strategy */
- </b>/* note : additional experimental parameters are also available<b>
- * within the experimental section of the API.
- * At the time of this writing, they include :
- * ZSTD_c_rsyncable
- * ZSTD_c_format
- * ZSTD_c_forceMaxWindow
- * ZSTD_c_forceAttachDict
- * ZSTD_c_literalCompressionMode
- * ZSTD_c_targetCBlockSize
- * ZSTD_c_srcSizeHint
- * ZSTD_c_enableDedicatedDictSearch
- * ZSTD_c_stableInBuffer
- * ZSTD_c_stableOutBuffer
- * ZSTD_c_blockDelimiters
- * ZSTD_c_validateSequences
- * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them.
- * note : never ever use experimentalParam? names directly;
- * also, the enums values themselves are unstable and can still change.
- */
- ZSTD_c_experimentalParam1=500,
- ZSTD_c_experimentalParam2=10,
- ZSTD_c_experimentalParam3=1000,
- ZSTD_c_experimentalParam4=1001,
- ZSTD_c_experimentalParam5=1002,
- ZSTD_c_experimentalParam6=1003,
- ZSTD_c_experimentalParam7=1004,
- ZSTD_c_experimentalParam8=1005,
- ZSTD_c_experimentalParam9=1006,
- ZSTD_c_experimentalParam10=1007,
- ZSTD_c_experimentalParam11=1008,
- ZSTD_c_experimentalParam12=1009
- } ZSTD_cParameter;
- </b></pre><BR>
- <pre><b>typedef struct {
- size_t error;
- int lowerBound;
- int upperBound;
- } ZSTD_bounds;
- </b></pre><BR>
- <pre><b>ZSTD_bounds ZSTD_cParam_getBounds(ZSTD_cParameter cParam);
- </b><p> All parameters must belong to an interval with lower and upper bounds,
- otherwise they will either trigger an error or be automatically clamped.
- @return : a structure, ZSTD_bounds, which contains
- - an error status field, which must be tested using ZSTD_isError()
- - lower and upper bounds, both inclusive
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int value);
- </b><p> Set one compression parameter, selected by enum ZSTD_cParameter.
- All parameters have valid bounds. Bounds can be queried using ZSTD_cParam_getBounds().
- Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter).
- Setting a parameter is generally only possible during frame initialization (before starting compression).
- Exception : when using multi-threading mode (nbWorkers >= 1),
- the following parameters can be updated _during_ compression (within same frame):
- => compressionLevel, hashLog, chainLog, searchLog, minMatch, targetLength and strategy.
- new parameters will be active for next job only (after a flush()).
- @return : an error code (which can be tested using ZSTD_isError()).
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize);
- </b><p> Total input data size to be compressed as a single frame.
- Value will be written in frame header, unless if explicitly forbidden using ZSTD_c_contentSizeFlag.
- This value will also be controlled at end of frame, and trigger an error if not respected.
- @result : 0, or an error code (which can be tested with ZSTD_isError()).
- Note 1 : pledgedSrcSize==0 actually means zero, aka an empty frame.
- In order to mean "unknown content size", pass constant ZSTD_CONTENTSIZE_UNKNOWN.
- ZSTD_CONTENTSIZE_UNKNOWN is default value for any new frame.
- Note 2 : pledgedSrcSize is only valid once, for the next frame.
- It's discarded at the end of the frame, and replaced by ZSTD_CONTENTSIZE_UNKNOWN.
- Note 3 : Whenever all input data is provided and consumed in a single round,
- for example with ZSTD_compress2(),
- or invoking immediately ZSTD_compressStream2(,,,ZSTD_e_end),
- this value is automatically overridden by srcSize instead.
-
- </p></pre><BR>
- <pre><b>typedef enum {
- ZSTD_reset_session_only = 1,
- ZSTD_reset_parameters = 2,
- ZSTD_reset_session_and_parameters = 3
- } ZSTD_ResetDirective;
- </b></pre><BR>
- <pre><b>size_t ZSTD_CCtx_reset(ZSTD_CCtx* cctx, ZSTD_ResetDirective reset);
- </b><p> There are 2 different things that can be reset, independently or jointly :
- - The session : will stop compressing current frame, and make CCtx ready to start a new one.
- Useful after an error, or to interrupt any ongoing compression.
- Any internal data not yet flushed is cancelled.
- Compression parameters and dictionary remain unchanged.
- They will be used to compress next frame.
- Resetting session never fails.
- - The parameters : changes all parameters back to "default".
- This removes any reference to any dictionary too.
- Parameters can only be changed between 2 sessions (i.e. no compression is currently ongoing)
- otherwise the reset fails, and function returns an error value (which can be tested using ZSTD_isError())
- - Both : similar to resetting the session, followed by resetting parameters.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_compress2( ZSTD_CCtx* cctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize);
- </b><p> Behave the same as ZSTD_compressCCtx(), but compression parameters are set using the advanced API.
- ZSTD_compress2() always starts a new frame.
- Should cctx hold data from a previously unfinished frame, everything about it is forgotten.
- - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*()
- - The function is always blocking, returns when compression is completed.
- Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
- @return : compressed size written into `dst` (<= `dstCapacity),
- or an error code if it fails (which can be tested using ZSTD_isError()).
-
- </p></pre><BR>
- <a name="Chapter6"></a><h2>Advanced decompression API</h2><pre></pre>
- <pre><b>typedef enum {
- ZSTD_d_windowLogMax=100, </b>/* Select a size limit (in power of 2) beyond which<b>
- * the streaming API will refuse to allocate memory buffer
- * in order to protect the host from unreasonable memory requirements.
- * This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode.
- * By default, a decompression context accepts window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT).
- * Special: value 0 means "use default maximum windowLog". */
- </b>/* note : additional experimental parameters are also available<b>
- * within the experimental section of the API.
- * At the time of this writing, they include :
- * ZSTD_d_format
- * ZSTD_d_stableOutBuffer
- * ZSTD_d_forceIgnoreChecksum
- * ZSTD_d_refMultipleDDicts
- * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them.
- * note : never ever use experimentalParam? names directly
- */
- ZSTD_d_experimentalParam1=1000,
- ZSTD_d_experimentalParam2=1001,
- ZSTD_d_experimentalParam3=1002,
- ZSTD_d_experimentalParam4=1003
- } ZSTD_dParameter;
- </b></pre><BR>
- <pre><b>ZSTD_bounds ZSTD_dParam_getBounds(ZSTD_dParameter dParam);
- </b><p> All parameters must belong to an interval with lower and upper bounds,
- otherwise they will either trigger an error or be automatically clamped.
- @return : a structure, ZSTD_bounds, which contains
- - an error status field, which must be tested using ZSTD_isError()
- - both lower and upper bounds, inclusive
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_setParameter(ZSTD_DCtx* dctx, ZSTD_dParameter param, int value);
- </b><p> Set one compression parameter, selected by enum ZSTD_dParameter.
- All parameters have valid bounds. Bounds can be queried using ZSTD_dParam_getBounds().
- Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter).
- Setting a parameter is only possible during frame initialization (before starting decompression).
- @return : 0, or an error code (which can be tested using ZSTD_isError()).
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_reset(ZSTD_DCtx* dctx, ZSTD_ResetDirective reset);
- </b><p> Return a DCtx to clean state.
- Session and parameters can be reset jointly or separately.
- Parameters can only be reset when no active frame is being decompressed.
- @return : 0, or an error code, which can be tested with ZSTD_isError()
-
- </p></pre><BR>
- <a name="Chapter7"></a><h2>Streaming</h2><pre></pre>
- <pre><b>typedef struct ZSTD_inBuffer_s {
- const void* src; </b>/**< start of input buffer */<b>
- size_t size; </b>/**< size of input buffer */<b>
- size_t pos; </b>/**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
- } ZSTD_inBuffer;
- </b></pre><BR>
- <pre><b>typedef struct ZSTD_outBuffer_s {
- void* dst; </b>/**< start of output buffer */<b>
- size_t size; </b>/**< size of output buffer */<b>
- size_t pos; </b>/**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
- } ZSTD_outBuffer;
- </b></pre><BR>
- <a name="Chapter8"></a><h2>Streaming compression - HowTo</h2><pre>
- A ZSTD_CStream object is required to track streaming operation.
- Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources.
- ZSTD_CStream objects can be reused multiple times on consecutive compression operations.
- It is recommended to re-use ZSTD_CStream since it will play nicer with system's memory, by re-using already allocated memory.
- For parallel execution, use one separate ZSTD_CStream per thread.
- note : since v1.3.0, ZSTD_CStream and ZSTD_CCtx are the same thing.
- Parameters are sticky : when starting a new compression on the same context,
- it will re-use the same sticky parameters as previous compression session.
- When in doubt, it's recommended to fully initialize the context before usage.
- Use ZSTD_CCtx_reset() to reset the context and ZSTD_CCtx_setParameter(),
- ZSTD_CCtx_setPledgedSrcSize(), or ZSTD_CCtx_loadDictionary() and friends to
- set more specific parameters, the pledged source size, or load a dictionary.
- Use ZSTD_compressStream2() with ZSTD_e_continue as many times as necessary to
- consume input stream. The function will automatically update both `pos`
- fields within `input` and `output`.
- Note that the function may not consume the entire input, for example, because
- the output buffer is already full, in which case `input.pos < input.size`.
- The caller must check if input has been entirely consumed.
- If not, the caller must make some room to receive more compressed data,
- and then present again remaining input data.
- note: ZSTD_e_continue is guaranteed to make some forward progress when called,
- but doesn't guarantee maximal forward progress. This is especially relevant
- when compressing with multiple threads. The call won't block if it can
- consume some input, but if it can't it will wait for some, but not all,
- output to be flushed.
- @return : provides a minimum amount of data remaining to be flushed from internal buffers
- or an error code, which can be tested using ZSTD_isError().
- At any moment, it's possible to flush whatever data might remain stuck within internal buffer,
- using ZSTD_compressStream2() with ZSTD_e_flush. `output->pos` will be updated.
- Note that, if `output->size` is too small, a single invocation with ZSTD_e_flush might not be enough (return code > 0).
- In which case, make some room to receive more compressed data, and call again ZSTD_compressStream2() with ZSTD_e_flush.
- You must continue calling ZSTD_compressStream2() with ZSTD_e_flush until it returns 0, at which point you can change the
- operation.
- note: ZSTD_e_flush will flush as much output as possible, meaning when compressing with multiple threads, it will
- block until the flush is complete or the output buffer is full.
- @return : 0 if internal buffers are entirely flushed,
- >0 if some data still present within internal buffer (the value is minimal estimation of remaining size),
- or an error code, which can be tested using ZSTD_isError().
- Calling ZSTD_compressStream2() with ZSTD_e_end instructs to finish a frame.
- It will perform a flush and write frame epilogue.
- The epilogue is required for decoders to consider a frame completed.
- flush operation is the same, and follows same rules as calling ZSTD_compressStream2() with ZSTD_e_flush.
- You must continue calling ZSTD_compressStream2() with ZSTD_e_end until it returns 0, at which point you are free to
- start a new frame.
- note: ZSTD_e_end will flush as much output as possible, meaning when compressing with multiple threads, it will
- block until the flush is complete or the output buffer is full.
- @return : 0 if frame fully completed and fully flushed,
- >0 if some data still present within internal buffer (the value is minimal estimation of remaining size),
- or an error code, which can be tested using ZSTD_isError().
-
- <BR></pre>
- <pre><b>typedef ZSTD_CCtx ZSTD_CStream; </b>/**< CCtx and CStream are now effectively same object (>= v1.3.0) */<b>
- </b></pre><BR>
- <h3>ZSTD_CStream management functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream(void);
- size_t ZSTD_freeCStream(ZSTD_CStream* zcs);
- </pre></b><BR>
- <h3>Streaming compression functions</h3><pre></pre><b><pre>typedef enum {
- ZSTD_e_continue=0, </b>/* collect more data, encoder decides when to output compressed result, for optimal compression ratio */<b>
- ZSTD_e_flush=1, </b>/* flush any data provided so far,<b>
- * it creates (at least) one new block, that can be decoded immediately on reception;
- * frame will continue: any future data can still reference previously compressed data, improving compression.
- * note : multithreaded compression will block to flush as much output as possible. */
- ZSTD_e_end=2 </b>/* flush any remaining data _and_ close current frame.<b>
- * note that frame is only closed after compressed data is fully flushed (return value == 0).
- * After that point, any additional data starts a new frame.
- * note : each frame is independent (does not reference any content from previous frame).
- : note : multithreaded compression will block to flush as much output as possible. */
- } ZSTD_EndDirective;
- </pre></b><BR>
- <pre><b>size_t ZSTD_compressStream2( ZSTD_CCtx* cctx,
- ZSTD_outBuffer* output,
- ZSTD_inBuffer* input,
- ZSTD_EndDirective endOp);
- </b><p> Behaves about the same as ZSTD_compressStream, with additional control on end directive.
- - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*()
- - Compression parameters cannot be changed once compression is started (save a list of exceptions in multi-threading mode)
- - output->pos must be <= dstCapacity, input->pos must be <= srcSize
- - output->pos and input->pos will be updated. They are guaranteed to remain below their respective limit.
- - endOp must be a valid directive
- - When nbWorkers==0 (default), function is blocking : it completes its job before returning to caller.
- - When nbWorkers>=1, function is non-blocking : it copies a portion of input, distributes jobs to internal worker threads, flush to output whatever is available,
- and then immediately returns, just indicating that there is some data remaining to be flushed.
- The function nonetheless guarantees forward progress : it will return only after it reads or write at least 1+ byte.
- - Exception : if the first call requests a ZSTD_e_end directive and provides enough dstCapacity, the function delegates to ZSTD_compress2() which is always blocking.
- - @return provides a minimum amount of data remaining to be flushed from internal buffers
- or an error code, which can be tested using ZSTD_isError().
- if @return != 0, flush is not fully completed, there is still some data left within internal buffers.
- This is useful for ZSTD_e_flush, since in this case more flushes are necessary to empty all buffers.
- For ZSTD_e_end, @return == 0 when internal buffers are fully flushed and frame is completed.
- - after a ZSTD_e_end directive, if internal buffer is not fully flushed (@return != 0),
- only ZSTD_e_end or ZSTD_e_flush operations are allowed.
- Before starting a new compression job, or changing compression parameters,
- it is required to fully flush internal buffers.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_CStreamInSize(void); </b>/**< recommended size for input buffer */<b>
- </b></pre><BR>
- <pre><b>size_t ZSTD_CStreamOutSize(void); </b>/**< recommended size for output buffer. Guarantee to successfully flush at least one complete compressed block. */<b>
- </b></pre><BR>
- <pre><b>size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel);
- </b>/*!<b>
- * Alternative for ZSTD_compressStream2(zcs, output, input, ZSTD_e_continue).
- * NOTE: The return value is different. ZSTD_compressStream() returns a hint for
- * the next read size (if non-zero and not an error). ZSTD_compressStream2()
- * returns the minimum nb of bytes left to flush (if non-zero and not an error).
- */
- size_t ZSTD_compressStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
- </b>/*! Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_flush). */<b>
- size_t ZSTD_flushStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
- </b>/*! Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_end). */<b>
- size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
- </b><p>
- ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
- ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any)
- ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel);
-
- </p></pre><BR>
- <a name="Chapter9"></a><h2>Streaming decompression - HowTo</h2><pre>
- A ZSTD_DStream object is required to track streaming operations.
- Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources.
- ZSTD_DStream objects can be re-used multiple times.
- Use ZSTD_initDStream() to start a new decompression operation.
- @return : recommended first input size
- Alternatively, use advanced API to set specific properties.
- Use ZSTD_decompressStream() repetitively to consume your input.
- The function will update both `pos` fields.
- If `input.pos < input.size`, some input has not been consumed.
- It's up to the caller to present again remaining data.
- The function tries to flush all data decoded immediately, respecting output buffer size.
- If `output.pos < output.size`, decoder has flushed everything it could.
- But if `output.pos == output.size`, there might be some data left within internal buffers.,
- In which case, call ZSTD_decompressStream() again to flush whatever remains in the buffer.
- Note : with no additional input provided, amount of data flushed is necessarily <= ZSTD_BLOCKSIZE_MAX.
- @return : 0 when a frame is completely decoded and fully flushed,
- or an error code, which can be tested using ZSTD_isError(),
- or any other value > 0, which means there is still some decoding or flushing to do to complete current frame :
- the return value is a suggested next input size (just a hint for better latency)
- that will never request more than the remaining frame size.
-
- <BR></pre>
- <pre><b>typedef ZSTD_DCtx ZSTD_DStream; </b>/**< DCtx and DStream are now effectively same object (>= v1.3.0) */<b>
- </b></pre><BR>
- <h3>ZSTD_DStream management functions</h3><pre></pre><b><pre>ZSTD_DStream* ZSTD_createDStream(void);
- size_t ZSTD_freeDStream(ZSTD_DStream* zds);
- </pre></b><BR>
- <h3>Streaming decompression functions</h3><pre></pre><b><pre></pre></b><BR>
- <pre><b>size_t ZSTD_DStreamInSize(void); </b>/*!< recommended size for input buffer */<b>
- </b></pre><BR>
- <pre><b>size_t ZSTD_DStreamOutSize(void); </b>/*!< recommended size for output buffer. Guarantee to successfully flush at least one complete block in all circumstances. */<b>
- </b></pre><BR>
- <a name="Chapter10"></a><h2>Simple dictionary API</h2><pre></pre>
- <pre><b>size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- const void* dict,size_t dictSize,
- int compressionLevel);
- </b><p> Compression at an explicit compression level using a Dictionary.
- A dictionary can be any arbitrary data segment (also called a prefix),
- or a buffer with specified information (see dictBuilder/zdict.h).
- Note : This function loads the dictionary, resulting in significant startup delay.
- It's intended for a dictionary used only once.
- Note 2 : When `dict == NULL || dictSize < 8` no dictionary is used.
- </p></pre><BR>
- <pre><b>size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- const void* dict,size_t dictSize);
- </b><p> Decompression using a known Dictionary.
- Dictionary must be identical to the one used during compression.
- Note : This function loads the dictionary, resulting in significant startup delay.
- It's intended for a dictionary used only once.
- Note : When `dict == NULL || dictSize < 8` no dictionary is used.
- </p></pre><BR>
- <a name="Chapter11"></a><h2>Bulk processing dictionary API</h2><pre></pre>
- <pre><b>ZSTD_CDict* ZSTD_createCDict(const void* dictBuffer, size_t dictSize,
- int compressionLevel);
- </b><p> When compressing multiple messages or blocks using the same dictionary,
- it's recommended to digest the dictionary only once, since it's a costly operation.
- ZSTD_createCDict() will create a state from digesting a dictionary.
- The resulting state can be used for future compression operations with very limited startup cost.
- ZSTD_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only.
- @dictBuffer can be released after ZSTD_CDict creation, because its content is copied within CDict.
- Note 1 : Consider experimental function `ZSTD_createCDict_byReference()` if you prefer to not duplicate @dictBuffer content.
- Note 2 : A ZSTD_CDict can be created from an empty @dictBuffer,
- in which case the only thing that it transports is the @compressionLevel.
- This can be useful in a pipeline featuring ZSTD_compress_usingCDict() exclusively,
- expecting a ZSTD_CDict parameter with any data, including those without a known dictionary.
- </p></pre><BR>
- <pre><b>size_t ZSTD_freeCDict(ZSTD_CDict* CDict);
- </b><p> Function frees memory allocated by ZSTD_createCDict().
- </p></pre><BR>
- <pre><b>size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- const ZSTD_CDict* cdict);
- </b><p> Compression using a digested Dictionary.
- Recommended when same dictionary is used multiple times.
- Note : compression level is _decided at dictionary creation time_,
- and frame parameters are hardcoded (dictID=yes, contentSize=yes, checksum=no)
- </p></pre><BR>
- <pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dictBuffer, size_t dictSize);
- </b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
- dictBuffer can be released after DDict creation, as its content is copied inside DDict.
- </p></pre><BR>
- <pre><b>size_t ZSTD_freeDDict(ZSTD_DDict* ddict);
- </b><p> Function frees memory allocated with ZSTD_createDDict()
- </p></pre><BR>
- <pre><b>size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- const ZSTD_DDict* ddict);
- </b><p> Decompression using a digested Dictionary.
- Recommended when same dictionary is used multiple times.
- </p></pre><BR>
- <a name="Chapter12"></a><h2>Dictionary helper functions</h2><pre></pre>
- <pre><b>unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize);
- </b><p> Provides the dictID stored within dictionary.
- if @return == 0, the dictionary is not conformant with Zstandard specification.
- It can still be loaded, but as a content-only dictionary.
- </p></pre><BR>
- <pre><b>unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict);
- </b><p> Provides the dictID of the dictionary loaded into `ddict`.
- If @return == 0, the dictionary is not conformant to Zstandard specification, or empty.
- Non-conformant dictionaries can still be loaded, but as content-only dictionaries.
- </p></pre><BR>
- <pre><b>unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
- </b><p> Provides the dictID required to decompressed the frame stored within `src`.
- If @return == 0, the dictID could not be decoded.
- This could for one of the following reasons :
- - The frame does not require a dictionary to be decoded (most common case).
- - The frame was built with dictID intentionally removed. Whatever dictionary is necessary is a hidden information.
- Note : this use case also happens when using a non-conformant dictionary.
- - `srcSize` is too small, and as a result, the frame header could not be decoded (only possible if `srcSize < ZSTD_FRAMEHEADERSIZE_MAX`).
- - This is not a Zstandard frame.
- When identifying the exact failure cause, it's possible to use ZSTD_getFrameHeader(), which will provide a more precise error code.
- </p></pre><BR>
- <a name="Chapter13"></a><h2>Advanced dictionary and prefix API</h2><pre>
- This API allows dictionaries to be used with ZSTD_compress2(),
- ZSTD_compressStream2(), and ZSTD_decompress(). Dictionaries are sticky, and
- only reset with the context is reset with ZSTD_reset_parameters or
- ZSTD_reset_session_and_parameters. Prefixes are single-use.
- <BR></pre>
- <pre><b>size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize);
- </b><p> Create an internal CDict from `dict` buffer.
- Decompression will have to use same dictionary.
- @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 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,
- compression parameters can no longer be changed after loading a dictionary.
- Note 3 :`dict` content will be copied internally.
- Use experimental ZSTD_CCtx_loadDictionary_byReference() to reference content instead.
- In such a case, dictionary buffer must outlive its users.
- Note 4 : Use ZSTD_CCtx_loadDictionary_advanced()
- to precisely select how dictionary content must be interpreted.
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict);
- </b><p> Reference a prepared dictionary, to be used for all next 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.
- The ignored parameters will be used again if the CCtx is returned to no-dictionary mode.
- The dictionary will remain valid for future compressed frames using same CCtx.
- @result : 0, or an error code (which can be tested with ZSTD_isError()).
- Special : Referencing a NULL CDict means "return to no-dictionary mode".
- Note 1 : Currently, only one dictionary can be managed.
- Referencing a new dictionary effectively "discards" any previous one.
- Note 2 : CDict is just referenced, its lifetime must outlive its usage within CCtx.
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx,
- const void* prefix, size_t prefixSize);
- </b><p> Reference a prefix (single-usage dictionary) for next compressed frame.
- A prefix is **only used once**. Tables are discarded at end of frame (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).
- @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.
- Its content must remain unmodified during compression.
- 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_c_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 the same prefix multiple times, consider loadDictionary instead.
- Note 4 : By default, the prefix is interpreted as raw content (ZSTD_dct_rawContent).
- Use experimental ZSTD_CCtx_refPrefix_advanced() to alter dictionary interpretation.
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_loadDictionary(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
- </b><p> 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.
- @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".
- Note 1 : Loading a dictionary involves building tables,
- which has a non-negligible impact on CPU usage and latency.
- It's recommended to "load once, use many times", to amortize the cost
- Note 2 :`dict` content will be copied internally, so `dict` can be released after loading.
- Use ZSTD_DCtx_loadDictionary_byReference() to reference dictionary content instead.
- Note 3 : Use ZSTD_DCtx_loadDictionary_advanced() to take control of
- how dictionary content is loaded and interpreted.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_refDDict(ZSTD_DCtx* dctx, const ZSTD_DDict* ddict);
- </b><p> Reference a prepared dictionary, to be used to decompress next frames.
- The dictionary remains active for decompression of future frames using same DCtx.
- If called with ZSTD_d_refMultipleDDicts enabled, repeated calls of this function
- will store the DDict references in a table, and the DDict used for decompression
- will be determined at decompression time, as per the dict ID in the frame.
- The memory for the table is allocated on the first call to refDDict, and can be
- freed with ZSTD_freeDCtx().
- @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.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_refPrefix(ZSTD_DCtx* dctx,
- const void* prefix, size_t prefixSize);
- </b><p> Reference a prefix (single-usage dictionary) to decompress next frame.
- 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_decompressStream() returns 0.
- @result : 0, or an error code (which can be tested with ZSTD_isError()).
- Note 1 : Adding any prefix (including NULL) invalidates any previously set prefix or dictionary
- Note 2 : Prefix buffer is referenced. It **must** outlive decompression.
- Prefix buffer must remain unmodified up to the end of frame,
- reached when ZSTD_decompressStream() returns 0.
- Note 3 : By default, the prefix is treated as raw content (ZSTD_dct_rawContent).
- Use ZSTD_CCtx_refPrefix_advanced() to alter dictMode (Experimental section)
- Note 4 : Referencing a raw content prefix has almost no cpu nor memory cost.
- A full dictionary is more costly, as it requires building tables.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
- size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);
- size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs);
- size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds);
- size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
- size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
- </b><p> These functions give the _current_ memory usage of selected object.
- Note that object memory usage can evolve (increase or decrease) over time.
- </p></pre><BR>
- <a name="Chapter14"></a><h2>experimental API (static linking only)</h2><pre>
- The following symbols and constants
- are not planned to join "stable API" status in the near future.
- They can still change in future versions.
- Some of them are planned to remain in the static_only section indefinitely.
- Some of them might be removed in the future (especially when redundant with existing stable functions)
-
- <BR></pre>
- <pre><b>typedef struct {
- unsigned int offset; </b>/* The offset of the match. (NOT the same as the offset code)<b>
- * If offset == 0 and matchLength == 0, this sequence represents the last
- * literals in the block of litLength size.
- */
- unsigned int litLength; </b>/* Literal length of the sequence. */<b>
- unsigned int matchLength; </b>/* Match length of the sequence. */<b>
- </b>/* Note: Users of this API may provide a sequence with matchLength == litLength == offset == 0.<b>
- * In this case, we will treat the sequence as a marker for a block boundary.
- */
- unsigned int rep; </b>/* Represents which repeat offset is represented by the field 'offset'.<b>
- * 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_generateSequences() will calculate the value of
- * 'rep', but repeat offsets do not necessarily need to be calculated from an external
- * sequence provider's perspective. For example, ZSTD_compressSequences() does not
- * use this 'rep' field at all (as of now).
- */
- } ZSTD_Sequence;
- </b></pre><BR>
- <pre><b>typedef struct {
- unsigned windowLog; </b>/**< largest match distance : larger == more compression, more memory needed during decompression */<b>
- unsigned chainLog; </b>/**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */<b>
- unsigned hashLog; </b>/**< dispatch table : larger == faster, more memory */<b>
- unsigned searchLog; </b>/**< nb of searches : larger == more compression, slower */<b>
- unsigned minMatch; </b>/**< match length searched : larger == faster decompression, sometimes less compression */<b>
- unsigned targetLength; </b>/**< acceptable match size for optimal parser (only) : larger == more compression, slower */<b>
- ZSTD_strategy strategy; </b>/**< see ZSTD_strategy definition above */<b>
- } ZSTD_compressionParameters;
- </b></pre><BR>
- <pre><b>typedef struct {
- int contentSizeFlag; </b>/**< 1: content size will be in frame header (when known) */<b>
- int checksumFlag; </b>/**< 1: generate a 32-bits checksum using XXH64 algorithm at end of frame, for error detection */<b>
- int noDictIDFlag; </b>/**< 1: no dictID will be saved into frame header (dictID is only useful for dictionary compression) */<b>
- } ZSTD_frameParameters;
- </b></pre><BR>
- <pre><b>typedef struct {
- ZSTD_compressionParameters cParams;
- ZSTD_frameParameters fParams;
- } ZSTD_parameters;
- </b></pre><BR>
- <pre><b>typedef enum {
- ZSTD_dct_auto = 0, </b>/* dictionary is "full" when starting with ZSTD_MAGIC_DICTIONARY, otherwise it is "rawContent" */<b>
- ZSTD_dct_rawContent = 1, </b>/* ensures dictionary is always loaded as rawContent, even if it starts with ZSTD_MAGIC_DICTIONARY */<b>
- ZSTD_dct_fullDict = 2 </b>/* refuses to load a dictionary if it does not respect Zstandard's specification, starting with ZSTD_MAGIC_DICTIONARY */<b>
- } ZSTD_dictContentType_e;
- </b></pre><BR>
- <pre><b>typedef enum {
- ZSTD_dlm_byCopy = 0, </b>/**< Copy dictionary content internally */<b>
- ZSTD_dlm_byRef = 1 </b>/**< Reference dictionary content -- the dictionary buffer must outlive its users. */<b>
- } ZSTD_dictLoadMethod_e;
- </b></pre><BR>
- <pre><b>typedef enum {
- ZSTD_f_zstd1 = 0, </b>/* zstd frame format, specified in zstd_compression_format.md (default) */<b>
- ZSTD_f_zstd1_magicless = 1 </b>/* Variant of zstd frame format, without initial 4-bytes magic number.<b>
- * Useful to save 4 bytes per generated frame.
- * Decoder cannot recognise automatically this format, requiring this instruction. */
- } ZSTD_format_e;
- </b></pre><BR>
- <pre><b>typedef enum {
- </b>/* Note: this enum controls ZSTD_d_forceIgnoreChecksum */<b>
- ZSTD_d_validateChecksum = 0,
- ZSTD_d_ignoreChecksum = 1
- } ZSTD_forceIgnoreChecksum_e;
- </b></pre><BR>
- <pre><b>typedef enum {
- </b>/* Note: this enum controls ZSTD_d_refMultipleDDicts */<b>
- ZSTD_rmd_refSingleDDict = 0,
- ZSTD_rmd_refMultipleDDicts = 1
- } ZSTD_refMultipleDDicts_e;
- </b></pre><BR>
- <pre><b>typedef enum {
- </b>/* Note: this enum and the behavior it controls are effectively internal<b>
- * 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 three 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.
- *
- * - The CDict's tables are not used at all, and instead we use the working
- * context alone to reload the dictionary and use params based on the source
- * size. See ZSTD_compress_insertDictionary() and ZSTD_compress_usingDict().
- * This method is effective when the dictionary sizes are very small relative
- * to the input size, and the input size is fairly large to begin with.
- *
- * 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, </b>/* Use the default heuristic. */<b>
- ZSTD_dictForceAttach = 1, </b>/* Never copy the dictionary. */<b>
- ZSTD_dictForceCopy = 2, </b>/* Always copy the dictionary. */<b>
- ZSTD_dictForceLoad = 3 </b>/* Always reload the dictionary */<b>
- } ZSTD_dictAttachPref_e;
- </b></pre><BR>
- <pre><b>typedef enum {
- ZSTD_lcm_auto = 0, </b>/**< Automatically determine the compression mode based on the compression level.<b>
- * Negative compression levels will be uncompressed, and positive compression
- * levels will be compressed. */
- ZSTD_lcm_huffman = 1, </b>/**< Always attempt Huffman compression. Uncompressed literals will still be<b>
- * emitted if Huffman compression is not profitable. */
- ZSTD_lcm_uncompressed = 2 </b>/**< Always emit uncompressed literals. */<b>
- } ZSTD_literalCompressionMode_e;
- </b></pre><BR>
- <a name="Chapter15"></a><h2>Frame size functions</h2><pre></pre>
- <pre><b>unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize);
- </b><p> `src` should point to the start of a series of ZSTD encoded and/or skippable frames
- `srcSize` must be the _exact_ size of this series
- (i.e. there should be a frame boundary at `src + srcSize`)
- @return : - decompressed size of all data in all successive frames
- - if the decompressed size cannot be determined: ZSTD_CONTENTSIZE_UNKNOWN
- - if an error occurred: ZSTD_CONTENTSIZE_ERROR
- note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
- When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size.
- In which case, it's necessary to use streaming mode to decompress data.
- note 2 : decompressed size is always present when compression is done with ZSTD_compress()
- note 3 : decompressed size can be very large (64-bits value),
- potentially larger than what local system can handle as a single memory segment.
- In which case, it's necessary to use streaming mode to decompress data.
- note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified.
- Always ensure result fits within application's authorized limits.
- Each application can set its own limits.
- note 5 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to
- read each contained frame header. This is fast as most of the data is skipped,
- however it does mean that all frame data must be present and valid.
- </p></pre><BR>
- <pre><b>unsigned long long ZSTD_decompressBound(const void* src, size_t srcSize);
- </b><p> `src` should point to the start of a series of ZSTD encoded and/or skippable frames
- `srcSize` must be the _exact_ size of this series
- (i.e. there should be a frame boundary at `src + srcSize`)
- @return : - upper-bound for the decompressed size of all data in all successive frames
- - if an error occurred: ZSTD_CONTENTSIZE_ERROR
- note 1 : an error can occur if `src` contains an invalid or incorrectly formatted frame.
- note 2 : the upper-bound is exact when the decompressed size field is available in every ZSTD encoded frame of `src`.
- in this case, `ZSTD_findDecompressedSize` and `ZSTD_decompressBound` return the same value.
- note 3 : when the decompressed size field isn't available, the upper-bound for that frame is calculated by:
- upper-bound = # blocks * min(128 KB, Window_Size)
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize);
- </b><p> srcSize must be >= ZSTD_FRAMEHEADERSIZE_PREFIX.
- @return : size of the Frame Header,
- or an error code (if srcSize is too small)
- </p></pre><BR>
- <pre><b>typedef enum {
- ZSTD_sf_noBlockDelimiters = 0, </b>/* Representation of ZSTD_Sequence has no block delimiters, sequences only */<b>
- ZSTD_sf_explicitBlockDelimiters = 1 </b>/* Representation of ZSTD_Sequence contains explicit block delimiters */<b>
- } ZSTD_sequenceFormat_e;
- </b></pre><BR>
- <pre><b></b><p> Generate sequences using ZSTD_compress2, given a source buffer.
- Each block will end with a dummy sequence
- with offset == 0, matchLength == 0, and litLength == length of last literals.
- litLength may be == 0, and if so, then the sequence of (of: 0 ml: 0 ll: 0)
- simply acts as a block delimiter.
- zc can be used to insert custom compression params.
- This function invokes ZSTD_compress2
- The output of this function can be fed into ZSTD_compressSequences() with CCtx
- setting of ZSTD_c_blockDelimiters as ZSTD_sf_explicitBlockDelimiters
- @return : number of sequences generated
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_mergeBlockDelimiters(ZSTD_Sequence* sequences, size_t seqsSize);
- </b><p> Given an array of ZSTD_Sequence, remove all sequences that represent block delimiters/last literals
- by merging them into into the literals of the next sequence.
- As such, the final generated result has no explicit representation of block boundaries,
- and the final last literals segment is not represented in the sequences.
- The output of this function can be fed into ZSTD_compressSequences() with CCtx
- setting of ZSTD_c_blockDelimiters as ZSTD_sf_noBlockDelimiters
- @return : number of sequences left after merging
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_compressSequences(ZSTD_CCtx* const cctx, void* dst, size_t dstSize,
- const ZSTD_Sequence* inSeqs, size_t inSeqsSize,
- const void* src, size_t srcSize);
- </b><p> Compress an array of ZSTD_Sequence, generated from the original source buffer, into dst.
- If a dictionary is included, then the cctx should reference the dict. (see: ZSTD_CCtx_refCDict(), ZSTD_CCtx_loadDictionary(), etc.)
- The entire source is compressed into a single frame.
- The compression behavior changes based on cctx params. In particular:
- If ZSTD_c_blockDelimiters == ZSTD_sf_noBlockDelimiters, the array of ZSTD_Sequence is expected to contain
- no block delimiters (defined in ZSTD_Sequence). Block boundaries are roughly determined based on
- the block size derived from the cctx, and sequences may be split. This is the default setting.
- If ZSTD_c_blockDelimiters == ZSTD_sf_explicitBlockDelimiters, the array of ZSTD_Sequence is expected to contain
- block delimiters (defined in ZSTD_Sequence). Behavior is undefined if no block delimiters are provided.
- If ZSTD_c_validateSequences == 0, this function will blindly accept the sequences provided. Invalid sequences cause undefined
- behavior. If ZSTD_c_validateSequences == 1, then if sequence is invalid (see doc/zstd_compression_format.md for
- specifics regarding offset/matchlength requirements) then the function will bail out and return an error.
- In addition to the two adjustable experimental params, there are other important cctx params.
- - ZSTD_c_minMatch MUST be set as less than or equal to the smallest match generated by the match finder. It has a minimum value of ZSTD_MINMATCH_MIN.
- - ZSTD_c_compressionLevel accordingly adjusts the strength of the entropy coder, as it would in typical compression.
- - ZSTD_c_windowLog affects offset validation: this function will return an error at higher debug levels if a provided offset
- is larger than what the spec allows for a given window log and dictionary (if present). See: doc/zstd_compression_format.md
- Note: Repcodes are, as of now, always re-calculated within this function, so ZSTD_Sequence::rep is unused.
- Note 2: Once we integrate ability to ingest repcodes, the explicit block delims mode must respect those repcodes exactly,
- and cannot emit an RLE block that disagrees with the repcode history
- @return : final compressed size or a ZSTD error.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_writeSkippableFrame(void* dst, size_t dstCapacity,
- const void* src, size_t srcSize, unsigned magicVariant);
- </b><p> Generates a zstd skippable frame containing data given by src, and writes it to dst buffer.
- Skippable frames begin with a a 4-byte magic number. There are 16 possible choices of magic number,
- ranging from ZSTD_MAGIC_SKIPPABLE_START to ZSTD_MAGIC_SKIPPABLE_START+15.
- As such, the parameter magicVariant controls the exact skippable frame magic number variant used, so
- the magic number used will be ZSTD_MAGIC_SKIPPABLE_START + magicVariant.
- Returns an error if destination buffer is not large enough, if the source size is not representable
- with a 4-byte unsigned int, or if the parameter magicVariant is greater than 15 (and therefore invalid).
- @return : number of bytes written or a ZSTD error.
-
- </p></pre><BR>
- <a name="Chapter16"></a><h2>Memory management</h2><pre></pre>
- <pre><b>size_t ZSTD_estimateCCtxSize(int compressionLevel);
- size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams);
- size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params);
- size_t ZSTD_estimateDCtxSize(void);
- </b><p> These functions make it possible to estimate memory usage
- of a future {D,C}Ctx, before its creation.
- ZSTD_estimateCCtxSize() will provide a memory budget large enough
- for any compression level up to selected one.
- Note : Unlike ZSTD_estimateCStreamSize*(), this estimate
- does not include space for a window buffer.
- Therefore, the estimation is only guaranteed for single-shot compressions, not streaming.
- The estimate will assume the input may be arbitrarily large,
- which is the worst case.
- When srcSize can be bound by a known and rather "small" value,
- this fact can be used to provide a tighter estimation
- because the CCtx compression context will need less memory.
- This tighter estimation can be provided by more advanced functions
- ZSTD_estimateCCtxSize_usingCParams(), which can be used in tandem with ZSTD_getCParams(),
- and ZSTD_estimateCCtxSize_usingCCtxParams(), which can be used in tandem with ZSTD_CCtxParams_setParameter().
- Both can be used to estimate memory using custom compression parameters and arbitrary srcSize limits.
- Note 2 : only single-threaded compression is supported.
- ZSTD_estimateCCtxSize_usingCCtxParams() will return an error code if ZSTD_c_nbWorkers is >= 1.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_estimateCStreamSize(int compressionLevel);
- size_t ZSTD_estimateCStreamSize_usingCParams(ZSTD_compressionParameters cParams);
- size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params);
- size_t ZSTD_estimateDStreamSize(size_t windowSize);
- size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize);
- </b><p> ZSTD_estimateCStreamSize() will provide a budget large enough for any compression level up to selected one.
- It will also consider src size to be arbitrarily "large", which is worst case.
- If srcSize is known to always be small, ZSTD_estimateCStreamSize_usingCParams() can provide a tighter estimation.
- ZSTD_estimateCStreamSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel.
- ZSTD_estimateCStreamSize_usingCCtxParams() can be used in tandem with ZSTD_CCtxParams_setParameter(). Only single-threaded compression is supported. This function will return an error code if ZSTD_c_nbWorkers is >= 1.
- Note : CStream size estimation is only correct for single-threaded compression.
- ZSTD_DStream memory budget depends on window Size.
- This information can be passed manually, using ZSTD_estimateDStreamSize,
- or deducted from a valid frame Header, using ZSTD_estimateDStreamSize_fromFrame();
- Note : if streaming is init with function ZSTD_init?Stream_usingDict(),
- an internal ?Dict will be created, which additional size is not estimated here.
- In this case, get total size by adding ZSTD_estimate?DictSize
- </p></pre><BR>
- <pre><b>size_t ZSTD_estimateCDictSize(size_t dictSize, int compressionLevel);
- size_t ZSTD_estimateCDictSize_advanced(size_t dictSize, ZSTD_compressionParameters cParams, ZSTD_dictLoadMethod_e dictLoadMethod);
- size_t ZSTD_estimateDDictSize(size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod);
- </b><p> ZSTD_estimateCDictSize() will bet that src size is relatively "small", and content is copied, like ZSTD_createCDict().
- ZSTD_estimateCDictSize_advanced() makes it possible to control compression parameters precisely, like ZSTD_createCDict_advanced().
- Note : dictionaries created by reference (`ZSTD_dlm_byRef`) are logically smaller.
-
- </p></pre><BR>
- <pre><b>ZSTD_CCtx* ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize);
- ZSTD_CStream* ZSTD_initStaticCStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticCCtx() */<b>
- </b><p> Initialize an object using a pre-allocated fixed-size buffer.
- workspace: The memory area to emplace the object into.
- Provided pointer *must be 8-bytes aligned*.
- Buffer must outlive object.
- workspaceSize: Use ZSTD_estimate*Size() to determine
- how large workspace must be to support target scenario.
- @return : pointer to object (same address as workspace, just different type),
- or NULL if error (size too small, incorrect alignment, etc.)
- Note : zstd will never resize nor malloc() when using a static buffer.
- If the object requires more memory than available,
- zstd will just error out (typically ZSTD_error_memory_allocation).
- Note 2 : there is no corresponding "free" function.
- Since workspace is allocated externally, it must be freed externally too.
- Note 3 : cParams : use ZSTD_getCParams() to convert a compression level
- into its associated cParams.
- Limitation 1 : currently not compatible with internal dictionary creation, triggered by
- ZSTD_CCtx_loadDictionary(), ZSTD_initCStream_usingDict() or ZSTD_initDStream_usingDict().
- Limitation 2 : static cctx currently not compatible with multi-threading.
- Limitation 3 : static dctx is incompatible with legacy support.
-
- </p></pre><BR>
- <pre><b>ZSTD_DStream* ZSTD_initStaticDStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticDCtx() */<b>
- </b></pre><BR>
- <pre><b>typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size);
- typedef void (*ZSTD_freeFunction) (void* opaque, void* address);
- typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem;
- static
- #ifdef __GNUC__
- __attribute__((__unused__))
- #endif
- ZSTD_customMem const ZSTD_defaultCMem = { NULL, NULL, NULL }; </b>/**< this constant defers to stdlib's functions */<b>
- </b><p> These prototypes make it possible to pass your own allocation/free functions.
- ZSTD_customMem is provided at creation time, using ZSTD_create*_advanced() variants listed below.
- All allocation/free operations will be completed using these custom variants instead of regular <stdlib.h> ones.
-
- </p></pre><BR>
- <a name="Chapter17"></a><h2>Advanced compression functions</h2><pre></pre>
- <pre><b>ZSTD_CDict* ZSTD_createCDict_byReference(const void* dictBuffer, size_t dictSize, int compressionLevel);
- </b><p> Create a digested dictionary for compression
- Dictionary content is just referenced, not duplicated.
- As a consequence, `dictBuffer` **must** outlive CDict,
- and its content must remain unmodified throughout the lifetime of CDict.
- note: equivalent to ZSTD_createCDict_advanced(), with dictLoadMethod==ZSTD_dlm_byRef
- </p></pre><BR>
- <pre><b>unsigned ZSTD_getDictID_fromCDict(const ZSTD_CDict* cdict);
- </b><p> Provides the dictID of the dictionary loaded into `cdict`.
- If @return == 0, the dictionary is not conformant to Zstandard specification, or empty.
- Non-conformant dictionaries can still be loaded, but as content-only dictionaries.
- </p></pre><BR>
- <pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
- </b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize.
- `estimatedSrcSize` value is optional, select 0 if not known
- </p></pre><BR>
- <pre><b>ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
- </b><p> same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`.
- All fields of `ZSTD_frameParameters` are set to default : contentSize=1, checksum=0, noDictID=0
- </p></pre><BR>
- <pre><b>size_t ZSTD_checkCParams(ZSTD_compressionParameters params);
- </b><p> Ensure param values remain within authorized range.
- @return 0 on success, or an error code (can be checked with ZSTD_isError())
- </p></pre><BR>
- <pre><b>ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize);
- </b><p> optimize params for a given `srcSize` and `dictSize`.
- `srcSize` can be unknown, in which case use ZSTD_CONTENTSIZE_UNKNOWN.
- `dictSize` must be `0` when there is no dictionary.
- cPar can be invalid : all parameters will be clamped within valid range in the @return struct.
- This function never fails (wide contract)
- </p></pre><BR>
- <pre><b>size_t ZSTD_compress_advanced(ZSTD_CCtx* cctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- const void* dict,size_t dictSize,
- ZSTD_parameters params);
- </b><p> Note : this function is now DEPRECATED.
- It can be replaced by ZSTD_compress2(), in combination with ZSTD_CCtx_setParameter() and other parameter setters.
- This prototype will be marked as deprecated and generate compilation warning on reaching v1.5.x
- </p></pre><BR>
- <pre><b>size_t ZSTD_compress_usingCDict_advanced(ZSTD_CCtx* cctx,
- void* dst, size_t dstCapacity,
- const void* src, size_t srcSize,
- const ZSTD_CDict* cdict,
- ZSTD_frameParameters fParams);
- </b><p> Note : this function is now REDUNDANT.
- It can be replaced by ZSTD_compress2(), in combination with ZSTD_CCtx_loadDictionary() and other parameter setters.
- This prototype will be marked as deprecated and generate compilation warning in some future version
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtx_loadDictionary_byReference(ZSTD_CCtx* cctx, const void* dict, size_t dictSize);
- </b><p> Same as ZSTD_CCtx_loadDictionary(), but dictionary content is referenced, instead of being copied into CCtx.
- It saves some memory, but also requires that `dict` outlives its usage within `cctx`
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtx_loadDictionary_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod, ZSTD_dictContentType_e dictContentType);
- </b><p> Same as ZSTD_CCtx_loadDictionary(), but gives finer control over
- how to load the dictionary (by copy ? by reference ?)
- and how to interpret it (automatic ? force raw mode ? full mode only ?)
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtx_refPrefix_advanced(ZSTD_CCtx* cctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType);
- </b><p> Same as ZSTD_CCtx_refPrefix(), but gives finer control over
- how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?)
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtx_getParameter(const ZSTD_CCtx* cctx, ZSTD_cParameter param, int* value);
- </b><p> Get the requested compression parameter value, selected by enum ZSTD_cParameter,
- and store it into int* value.
- @return : 0, or an error code (which can be tested with ZSTD_isError()).
-
- </p></pre><BR>
- <pre><b>ZSTD_CCtx_params* ZSTD_createCCtxParams(void);
- size_t ZSTD_freeCCtxParams(ZSTD_CCtx_params* params);
- </b><p> Quick howto :
- - ZSTD_createCCtxParams() : Create a ZSTD_CCtx_params structure
- - ZSTD_CCtxParams_setParameter() : Push parameters one by one into
- an existing ZSTD_CCtx_params structure.
- This is similar to
- ZSTD_CCtx_setParameter().
- - ZSTD_CCtx_setParametersUsingCCtxParams() : Apply parameters to
- an existing CCtx.
- These parameters will be applied to
- all subsequent frames.
- - ZSTD_compressStream2() : Do compression using the CCtx.
- - ZSTD_freeCCtxParams() : Free the memory.
- This can be used with ZSTD_estimateCCtxSize_advanced_usingCCtxParams()
- for static allocation of CCtx for single-threaded compression.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtxParams_reset(ZSTD_CCtx_params* params);
- </b><p> Reset params to default values.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtxParams_init(ZSTD_CCtx_params* cctxParams, int compressionLevel);
- </b><p> Initializes the compression parameters of cctxParams according to
- compression level. All other parameters are reset to their default values.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtxParams_init_advanced(ZSTD_CCtx_params* cctxParams, ZSTD_parameters params);
- </b><p> Initializes the compression and frame parameters of cctxParams according to
- params. All other parameters are reset to their default values.
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtxParams_setParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int value);
- </b><p> Similar to ZSTD_CCtx_setParameter.
- Set one compression parameter, selected by enum ZSTD_cParameter.
- Parameters must be applied to a ZSTD_CCtx using
- ZSTD_CCtx_setParametersUsingCCtxParams().
- @result : a code representing success or failure (which can be tested with
- ZSTD_isError()).
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtxParams_getParameter(const ZSTD_CCtx_params* params, ZSTD_cParameter param, int* value);
- </b><p> Similar to ZSTD_CCtx_getParameter.
- Get the requested value of one compression parameter, selected by enum ZSTD_cParameter.
- @result : 0, or an error code (which can be tested with ZSTD_isError()).
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_CCtx_setParametersUsingCCtxParams(
- ZSTD_CCtx* cctx, const ZSTD_CCtx_params* params);
- </b><p> Apply a set of ZSTD_CCtx_params to the compression context.
- This can be done even after compression is started,
- if nbWorkers==0, this will have no impact until a new compression is started.
- if nbWorkers>=1, new parameters will be picked up at next job,
- with a few restrictions (windowLog, pledgedSrcSize, nbWorkers, jobSize, and overlapLog are not updated).
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_compressStream2_simpleArgs (
- ZSTD_CCtx* cctx,
- void* dst, size_t dstCapacity, size_t* dstPos,
- const void* src, size_t srcSize, size_t* srcPos,
- ZSTD_EndDirective endOp);
- </b><p> Same as ZSTD_compressStream2(),
- but using only integral types as arguments.
- This variant might be helpful for binders from dynamic languages
- which have troubles handling structures containing memory pointers.
-
- </p></pre><BR>
-
- <pre><b>int ZSTD_defaultCLevel();
- </b><p> Returns the default compression level, specified by ZSTD_CLEVEL_DEFAULT
- </p></pre><BR>
- <a name="Chapter18"></a><h2>Advanced decompression functions</h2><pre></pre>
- <pre><b>unsigned ZSTD_isFrame(const void* buffer, size_t size);
- </b><p> Tells if the content of `buffer` starts with a valid Frame Identifier.
- Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0.
- Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled.
- Note 3 : Skippable Frame Identifiers are considered valid.
- </p></pre><BR>
- <pre><b>ZSTD_DDict* ZSTD_createDDict_byReference(const void* dictBuffer, size_t dictSize);
- </b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
- Dictionary content is referenced, and therefore stays in dictBuffer.
- It is important that dictBuffer outlives DDict,
- it must remain read accessible throughout the lifetime of DDict
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_loadDictionary_byReference(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
- </b><p> Same as ZSTD_DCtx_loadDictionary(),
- but references `dict` content instead of copying it into `dctx`.
- This saves memory if `dict` remains around.,
- However, it's imperative that `dict` remains accessible (and unmodified) while being used, so it must outlive decompression.
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_loadDictionary_advanced(ZSTD_DCtx* dctx, const void* dict, size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod, ZSTD_dictContentType_e dictContentType);
- </b><p> Same as ZSTD_DCtx_loadDictionary(),
- but gives direct control over
- how to load the dictionary (by copy ? by reference ?)
- and how to interpret it (automatic ? force raw mode ? full mode only ?).
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_refPrefix_advanced(ZSTD_DCtx* dctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType);
- </b><p> Same as ZSTD_DCtx_refPrefix(), but gives finer control over
- how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?)
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_setMaxWindowSize(ZSTD_DCtx* dctx, size_t maxWindowSize);
- </b><p> Refuses allocating internal buffers for frames requiring a window size larger than provided limit.
- This protects a decoder context from reserving too much memory for itself (potential attack scenario).
- This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode.
- By default, a decompression context accepts all window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT)
- @return : 0, or an error code (which can be tested using ZSTD_isError()).
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_getParameter(ZSTD_DCtx* dctx, ZSTD_dParameter param, int* value);
- </b><p> Get the requested decompression parameter value, selected by enum ZSTD_dParameter,
- and store it into int* value.
- @return : 0, or an error code (which can be tested with ZSTD_isError()).
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_DCtx_setFormat(ZSTD_DCtx* dctx, ZSTD_format_e format);
- </b><p> Instruct the decoder context about what kind of data to decode next.
- This instruction is mandatory to decode data without a fully-formed header,
- such ZSTD_f_zstd1_magicless for example.
- @return : 0, or an error code (which can be tested using ZSTD_isError()).
- </p></pre><BR>
- <pre><b>size_t ZSTD_decompressStream_simpleArgs (
- ZSTD_DCtx* dctx,
- void* dst, size_t dstCapacity, size_t* dstPos,
- const void* src, size_t srcSize, size_t* srcPos);
- </b><p> Same as ZSTD_decompressStream(),
- but using only integral types as arguments.
- This can be helpful for binders from dynamic languages
- which have troubles handling structures containing memory pointers.
-
- </p></pre><BR>
- <a name="Chapter19"></a><h2>Advanced streaming functions</h2><pre> Warning : most of these functions are now redundant with the Advanced API.
- Once Advanced API reaches "stable" status,
- redundant functions will be deprecated, and then at some point removed.
- <BR></pre>
- <h3>Advanced Streaming compression functions</h3><pre></pre><b><pre></pre></b><BR>
- <pre><b>size_t
- ZSTD_initCStream_srcSize(ZSTD_CStream* zcs,
- int compressionLevel,
- unsigned long long pledgedSrcSize);
- </b><p> This function is deprecated, and equivalent to:
- ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
- ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any)
- ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel);
- ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
- pledgedSrcSize must be correct. If it is not known at init time, use
- ZSTD_CONTENTSIZE_UNKNOWN. Note that, for compatibility with older programs,
- "0" also disables frame content size field. It may be enabled in the future.
- Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x
-
- </p></pre><BR>
- <pre><b>size_t
- ZSTD_initCStream_usingDict(ZSTD_CStream* zcs,
- const void* dict, size_t dictSize,
- int compressionLevel);
- </b><p> This function is deprecated, and is equivalent to:
- ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
- ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel);
- ZSTD_CCtx_loadDictionary(zcs, dict, dictSize);
- Creates of an internal CDict (incompatible with static CCtx), except if
- dict == NULL or dictSize < 8, in which case no dict is used.
- Note: dict is loaded with ZSTD_dct_auto (treated as a full zstd dictionary if
- it begins with ZSTD_MAGIC_DICTIONARY, else as raw content) and ZSTD_dlm_byCopy.
- Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x
-
- </p></pre><BR>
- <pre><b>size_t
- ZSTD_initCStream_advanced(ZSTD_CStream* zcs,
- const void* dict, size_t dictSize,
- ZSTD_parameters params,
- unsigned long long pledgedSrcSize);
- </b><p> This function is deprecated, and is approximately equivalent to:
- ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
- // Pseudocode: Set each zstd parameter and leave the rest as-is.
- for ((param, value) : params) {
- ZSTD_CCtx_setParameter(zcs, param, value);
- }
- ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
- ZSTD_CCtx_loadDictionary(zcs, dict, dictSize);
- dict is loaded with ZSTD_dct_auto and ZSTD_dlm_byCopy.
- pledgedSrcSize must be correct.
- If srcSize is not known at init time, use value ZSTD_CONTENTSIZE_UNKNOWN.
- Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict);
- </b><p> This function is deprecated, and equivalent to:
- ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
- ZSTD_CCtx_refCDict(zcs, cdict);
- note : cdict will just be referenced, and must outlive compression session
- Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x
-
- </p></pre><BR>
- <pre><b>size_t
- ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs,
- const ZSTD_CDict* cdict,
- ZSTD_frameParameters fParams,
- unsigned long long pledgedSrcSize);
- </b><p> This function is DEPRECATED, and is approximately equivalent to:
- ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
- // Pseudocode: Set each zstd frame parameter and leave the rest as-is.
- for ((fParam, value) : fParams) {
- ZSTD_CCtx_setParameter(zcs, fParam, value);
- }
- ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
- ZSTD_CCtx_refCDict(zcs, cdict);
- same as ZSTD_initCStream_usingCDict(), with control over frame parameters.
- pledgedSrcSize must be correct. If srcSize is not known at init time, use
- value ZSTD_CONTENTSIZE_UNKNOWN.
- Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize);
- </b><p> This function is deprecated, and is equivalent to:
- ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only);
- ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize);
- start a new frame, using same parameters from previous frame.
- This is typically useful to skip dictionary loading stage, since it will re-use it in-place.
- Note that zcs must be init at least once before using ZSTD_resetCStream().
- If pledgedSrcSize is not known at reset time, use macro ZSTD_CONTENTSIZE_UNKNOWN.
- If pledgedSrcSize > 0, its value must be correct, as it will be written in header, and controlled at the end.
- For the time being, pledgedSrcSize==0 is interpreted as "srcSize unknown" for compatibility with older programs,
- but it will change to mean "empty" in future version, so use macro ZSTD_CONTENTSIZE_UNKNOWN instead.
- @return : 0, or an error code (which can be tested using ZSTD_isError())
- Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x
-
- </p></pre><BR>
- <pre><b>typedef struct {
- unsigned long long ingested; </b>/* nb input bytes read and buffered */<b>
- unsigned long long consumed; </b>/* nb input bytes actually compressed */<b>
- unsigned long long produced; </b>/* nb of compressed bytes generated and buffered */<b>
- unsigned long long flushed; </b>/* nb of compressed bytes flushed : not provided; can be tracked from caller side */<b>
- unsigned currentJobID; </b>/* MT only : latest started job nb */<b>
- unsigned nbActiveWorkers; </b>/* MT only : nb of workers actively compressing at probe time */<b>
- } ZSTD_frameProgression;
- </b></pre><BR>
- <pre><b>size_t ZSTD_toFlushNow(ZSTD_CCtx* cctx);
- </b><p> Tell how many bytes are ready to be flushed immediately.
- Useful for multithreading scenarios (nbWorkers >= 1).
- Probe the oldest active job, defined as oldest job not yet entirely flushed,
- and check its output buffer.
- @return : amount of data stored in oldest job and ready to be flushed immediately.
- if @return == 0, it means either :
- + there is no active job (could be checked with ZSTD_frameProgression()), or
- + oldest job is still actively compressing data,
- but everything it has produced has also been flushed so far,
- therefore flush speed is limited by production speed of oldest job
- irrespective of the speed of concurrent (and newer) jobs.
-
- </p></pre><BR>
- <h3>Advanced Streaming decompression functions</h3><pre></pre><b><pre></pre></b><BR>
- <pre><b>size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize);
- </b><p>
- ZSTD_DCtx_reset(zds, ZSTD_reset_session_only);
- ZSTD_DCtx_loadDictionary(zds, dict, dictSize);
- note: no dictionary will be used if dict == NULL or dictSize < 8
- Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_initDStream_usingDDict(ZSTD_DStream* zds, const ZSTD_DDict* ddict);
- </b><p>
- ZSTD_DCtx_reset(zds, ZSTD_reset_session_only);
- ZSTD_DCtx_refDDict(zds, ddict);
- note : ddict is referenced, it must outlive decompression session
- Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x
-
- </p></pre><BR>
- <pre><b>size_t ZSTD_resetDStream(ZSTD_DStream* zds);
- </b><p>
- ZSTD_DCtx_reset(zds, ZSTD_reset_session_only);
- re-use decompression parameters from previous init; saves dictionary loading
- Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x
-
- </p></pre><BR>
- <a name="Chapter20"></a><h2>Buffer-less and synchronous inner streaming functions</h2><pre>
- This is an advanced API, giving full control over buffer management, for users which need direct control over memory.
- But it's also a complex one, with several restrictions, documented below.
- Prefer normal streaming API for an easier experience.
-
- <BR></pre>
- <a name="Chapter21"></a><h2>Buffer-less streaming compression (synchronous mode)</h2><pre>
- A ZSTD_CCtx object is required to track streaming operations.
- Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource.
- ZSTD_CCtx object can be re-used multiple times within successive compression operations.
- Start by initializing a context.
- Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression,
- or ZSTD_compressBegin_advanced(), for finer parameter control.
- It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx()
- Then, consume your input using ZSTD_compressContinue().
- There are some important considerations to keep in mind when using this advanced function :
- - ZSTD_compressContinue() has no internal buffer. It uses externally provided buffers only.
- - Interface is synchronous : input is consumed entirely and produces 1+ compressed blocks.
- - Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario.
- Worst case evaluation is provided by ZSTD_compressBound().
- ZSTD_compressContinue() doesn't guarantee recover after a failed compression.
- - ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog).
- It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks)
- - ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps.
- In which case, it will "discard" the relevant memory section from its history.
- Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum.
- It's possible to use srcSize==0, in which case, it will write a final empty block to end the frame.
- Without last block mark, frames are considered unfinished (hence corrupted) by compliant decoders.
- `ZSTD_CCtx` object can be re-used (ZSTD_compressBegin()) to compress again.
- <BR></pre>
- <h3>Buffer-less streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel);
- size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel);
- size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_parameters params, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize : If srcSize is not known at init time, use ZSTD_CONTENTSIZE_UNKNOWN */<b>
- size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); </b>/**< note: fails if cdict==NULL */<b>
- size_t ZSTD_compressBegin_usingCDict_advanced(ZSTD_CCtx* const cctx, const ZSTD_CDict* const cdict, ZSTD_frameParameters const fParams, unsigned long long const pledgedSrcSize); </b>/* compression parameters are already set within cdict. pledgedSrcSize must be correct. If srcSize is not known, use macro ZSTD_CONTENTSIZE_UNKNOWN */<b>
- size_t ZSTD_copyCCtx(ZSTD_CCtx* cctx, const ZSTD_CCtx* preparedCCtx, unsigned long long pledgedSrcSize); </b>/**< note: if pledgedSrcSize is not known, use ZSTD_CONTENTSIZE_UNKNOWN */<b>
- </pre></b><BR>
- <a name="Chapter22"></a><h2>Buffer-less streaming decompression (synchronous mode)</h2><pre>
- A ZSTD_DCtx object is required to track streaming operations.
- Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it.
- A ZSTD_DCtx object can be re-used multiple times.
- First typical operation is to retrieve frame parameters, using ZSTD_getFrameHeader().
- Frame header is extracted from the beginning of compressed frame, so providing only the frame's beginning is enough.
- Data fragment must be large enough to ensure successful decoding.
- `ZSTD_frameHeaderSize_max` bytes is guaranteed to always be large enough.
- @result : 0 : successful decoding, the `ZSTD_frameHeader` structure is correctly filled.
- >0 : `srcSize` is too small, please provide at least @result bytes on next attempt.
- errorCode, which can be tested using ZSTD_isError().
- It fills a ZSTD_frameHeader structure with important information to correctly decode the frame,
- such as the dictionary ID, content size, or maximum back-reference distance (`windowSize`).
- Note that these values could be wrong, either because of data corruption, or because a 3rd party deliberately spoofs false information.
- As a consequence, check that values remain within valid application range.
- For example, do not allocate memory blindly, check that `windowSize` is within expectation.
- Each application can set its own limits, depending on local restrictions.
- For extended interoperability, it is recommended to support `windowSize` of at least 8 MB.
- ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize` bytes.
- ZSTD_decompressContinue() is very sensitive to contiguity,
- if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place,
- or that previous contiguous segment is large enough to properly handle maximum back-reference distance.
- There are multiple ways to guarantee this condition.
- The most memory efficient way is to use a round buffer of sufficient size.
- Sufficient size is determined by invoking ZSTD_decodingBufferSize_min(),
- which can @return an error code if required value is too large for current system (in 32-bits mode).
- In a round buffer methodology, ZSTD_decompressContinue() decompresses each block next to previous one,
- up to the moment there is not enough room left in the buffer to guarantee decoding another full block,
- which maximum size is provided in `ZSTD_frameHeader` structure, field `blockSizeMax`.
- At which point, decoding can resume from the beginning of the buffer.
- Note that already decoded data stored in the buffer should be flushed before being overwritten.
- There are alternatives possible, for example using two or more buffers of size `windowSize` each, though they consume more memory.
- Finally, if you control the compression process, you can also ignore all buffer size rules,
- as long as the encoder and decoder progress in "lock-step",
- aka use exactly the same buffer sizes, break contiguity at the same place, etc.
- Once buffers are setup, start decompression, with ZSTD_decompressBegin().
- If decompression requires a dictionary, use ZSTD_decompressBegin_usingDict() or ZSTD_decompressBegin_usingDDict().
- Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively.
- ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue().
- ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail.
- @result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity).
- It can be zero : it just means ZSTD_decompressContinue() has decoded some metadata item.
- It can also be an error code, which can be tested with ZSTD_isError().
- A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero.
- Context can then be reset to start a new decompression.
- Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType().
- This information is not required to properly decode a frame.
- == Special case : skippable frames
- Skippable frames allow integration of user-defined data into a flow of concatenated frames.
- Skippable frames will be ignored (skipped) by decompressor.
- The format of skippable frames is as follows :
- a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F
- b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits
- c) Frame Content - any content (User Data) of length equal to Frame Size
- For skippable frames ZSTD_getFrameHeader() returns zfhPtr->frameType==ZSTD_skippableFrame.
- For skippable frames ZSTD_decompressContinue() always returns 0 : it only skips the content.
- <BR></pre>
- <h3>Buffer-less streaming decompression functions</h3><pre></pre><b><pre>typedef enum { ZSTD_frame, ZSTD_skippableFrame } ZSTD_frameType_e;
- typedef struct {
- unsigned long long frameContentSize; </b>/* if == ZSTD_CONTENTSIZE_UNKNOWN, it means this field is not available. 0 means "empty" */<b>
- unsigned long long windowSize; </b>/* can be very large, up to <= frameContentSize */<b>
- unsigned blockSizeMax;
- ZSTD_frameType_e frameType; </b>/* if == ZSTD_skippableFrame, frameContentSize is the size of skippable content */<b>
- unsigned headerSize;
- unsigned dictID;
- unsigned checksumFlag;
- } ZSTD_frameHeader;
- </pre></b><BR>
- <pre><b>size_t ZSTD_getFrameHeader(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize); </b>/**< doesn't consume input */<b>
- </b>/*! ZSTD_getFrameHeader_advanced() :<b>
- * same as ZSTD_getFrameHeader(),
- * with added capability to select a format (like ZSTD_f_zstd1_magicless) */
- size_t ZSTD_getFrameHeader_advanced(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize, ZSTD_format_e format);
- size_t ZSTD_decodingBufferSize_min(unsigned long long windowSize, unsigned long long frameContentSize); </b>/**< when frame content size is not known, pass in frameContentSize == ZSTD_CONTENTSIZE_UNKNOWN */<b>
- </b><p> decode Frame Header, or requires larger `srcSize`.
- @return : 0, `zfhPtr` is correctly filled,
- >0, `srcSize` is too small, value is wanted `srcSize` amount,
- or an error code, which can be tested using ZSTD_isError()
- </p></pre><BR>
- <pre><b>typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e;
- </b></pre><BR>
- <a name="Chapter23"></a><h2>Block level API</h2><pre></pre>
- <pre><b></b><p> Frame metadata cost is typically ~12 bytes, which can be non-negligible for very small blocks (< 100 bytes).
- But users will have to take in charge needed metadata to regenerate data, such as compressed and content sizes.
- A few rules to respect :
- - Compressing and decompressing require a context structure
- + Use ZSTD_createCCtx() and ZSTD_createDCtx()
- - It is necessary to init context before starting
- + compression : any ZSTD_compressBegin*() variant, including with dictionary
- + decompression : any ZSTD_decompressBegin*() variant, including with dictionary
- + copyCCtx() and copyDCtx() can be used too
- - Block size is limited, it must be <= ZSTD_getBlockSize() <= ZSTD_BLOCKSIZE_MAX == 128 KB
- + If input is larger than a block size, it's necessary to split input data into multiple blocks
- + For inputs larger than a single block, consider using regular ZSTD_compress() instead.
- Frame metadata is not that costly, and quickly becomes negligible as source size grows larger than a block.
- - When a block is considered not compressible enough, ZSTD_compressBlock() result will be 0 (zero) !
- ===> In which case, nothing is produced into `dst` !
- + User __must__ test for such outcome and deal directly with uncompressed data
- + A block cannot be declared incompressible if ZSTD_compressBlock() return value was != 0.
- Doing so would mess up with statistics history, leading to potential data corruption.
- + ZSTD_decompressBlock() _doesn't accept uncompressed data as input_ !!
- + In case of multiple successive blocks, should some of them be uncompressed,
- decoder must be informed of their existence in order to follow proper history.
- Use ZSTD_insertBlock() for such a case.
- </p></pre><BR>
- <h3>Raw zstd block functions</h3><pre></pre><b><pre>size_t ZSTD_getBlockSize (const ZSTD_CCtx* cctx);
- size_t ZSTD_compressBlock (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
- size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
- size_t ZSTD_insertBlock (ZSTD_DCtx* dctx, const void* blockStart, size_t blockSize); </b>/**< insert uncompressed block into `dctx` history. Useful for multi-blocks decompression. */<b>
- </pre></b><BR>
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