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4 <title>zstd 1.3.8 Manual</title>
7 <h1>zstd 1.3.8 Manual</h1>
9 <a name="Contents"></a><h2>Contents</h2>
11 <li><a href="#Chapter1">Introduction</a></li>
12 <li><a href="#Chapter2">Version</a></li>
13 <li><a href="#Chapter3">Default constant</a></li>
14 <li><a href="#Chapter4">Simple API</a></li>
15 <li><a href="#Chapter5">Explicit context</a></li>
16 <li><a href="#Chapter6">Simple dictionary API</a></li>
17 <li><a href="#Chapter7">Bulk processing dictionary API</a></li>
18 <li><a href="#Chapter8">Streaming</a></li>
19 <li><a href="#Chapter9">Streaming compression - HowTo</a></li>
20 <li><a href="#Chapter10">Streaming decompression - HowTo</a></li>
21 <li><a href="#Chapter11">ADVANCED AND EXPERIMENTAL FUNCTIONS</a></li>
22 <li><a href="#Chapter12">Candidate API for promotion to stable status</a></li>
23 <li><a href="#Chapter13">Advanced compression API</a></li>
24 <li><a href="#Chapter14">experimental API (static linking only)</a></li>
25 <li><a href="#Chapter15">Frame size functions</a></li>
26 <li><a href="#Chapter16">Memory management</a></li>
27 <li><a href="#Chapter17">Advanced compression functions</a></li>
28 <li><a href="#Chapter18">Advanced decompression functions</a></li>
29 <li><a href="#Chapter19">Advanced streaming functions</a></li>
30 <li><a href="#Chapter20">Buffer-less and synchronous inner streaming functions</a></li>
31 <li><a href="#Chapter21">Buffer-less streaming compression (synchronous mode)</a></li>
32 <li><a href="#Chapter22">Buffer-less streaming decompression (synchronous mode)</a></li>
33 <li><a href="#Chapter23">ZSTD_getFrameHeader() :</a></li>
34 <li><a href="#Chapter24">Block level API</a></li>
37 <a name="Chapter1"></a><h2>Introduction</h2><pre>
38 zstd, short for Zstandard, is a fast lossless compression algorithm, targeting
39 real-time compression scenarios at zlib-level and better compression ratios.
40 The zstd compression library provides in-memory compression and decompression
43 The library supports regular compression levels from 1 up to ZSTD_maxCLevel(),
44 which is currently 22. Levels >= 20, labeled `--ultra`, should be used with
45 caution, as they require more memory. The library also offers negative
46 compression levels, which extend the range of speed vs. ratio preferences.
47 The lower the level, the faster the speed (at the cost of compression).
49 Compression can be done in:
50 - a single step (described as Simple API)
51 - a single step, reusing a context (described as Explicit context)
52 - unbounded multiple steps (described as Streaming compression)
54 The compression ratio achievable on small data can be highly improved using
55 a dictionary. Dictionary compression can be performed in:
56 - a single step (described as Simple dictionary API)
57 - a single step, reusing a dictionary (described as Bulk-processing
60 Advanced experimental functions can be accessed using
61 `#define ZSTD_STATIC_LINKING_ONLY` before including zstd.h.
63 Advanced experimental APIs should never be used with a dynamically-linked
64 library. They are not "stable"; their definitions or signatures may change in
65 the future. Only static linking is allowed.
68 <a name="Chapter2"></a><h2>Version</h2><pre></pre>
70 <pre><b>unsigned ZSTD_versionNumber(void); </b>/**< to check runtime library version */<b>
72 <a name="Chapter3"></a><h2>Default constant</h2><pre></pre>
74 <a name="Chapter4"></a><h2>Simple API</h2><pre></pre>
76 <pre><b>size_t ZSTD_compress( void* dst, size_t dstCapacity,
77 const void* src, size_t srcSize,
78 int compressionLevel);
79 </b><p> Compresses `src` content as a single zstd compressed frame into already allocated `dst`.
80 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
81 @return : compressed size written into `dst` (<= `dstCapacity),
82 or an error code if it fails (which can be tested using ZSTD_isError()).
85 <pre><b>size_t ZSTD_decompress( void* dst, size_t dstCapacity,
86 const void* src, size_t compressedSize);
87 </b><p> `compressedSize` : must be the _exact_ size of some number of compressed and/or skippable frames.
88 `dstCapacity` is an upper bound of originalSize to regenerate.
89 If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data.
90 @return : the number of bytes decompressed into `dst` (<= `dstCapacity`),
91 or an errorCode if it fails (which can be tested using ZSTD_isError()).
94 <pre><b>#define ZSTD_CONTENTSIZE_UNKNOWN (0ULL - 1)
95 #define ZSTD_CONTENTSIZE_ERROR (0ULL - 2)
96 unsigned long long ZSTD_getFrameContentSize(const void *src, size_t srcSize);
97 </b><p> `src` should point to the start of a ZSTD encoded frame.
98 `srcSize` must be at least as large as the frame header.
99 hint : any size >= `ZSTD_frameHeaderSize_max` is large enough.
100 @return : - decompressed size of `src` frame content, if known
101 - ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined
102 - ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small)
103 note 1 : a 0 return value means the frame is valid but "empty".
104 note 2 : decompressed size is an optional field, it may not be present, typically in streaming mode.
105 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size.
106 In which case, it's necessary to use streaming mode to decompress data.
107 Optionally, application can rely on some implicit limit,
108 as ZSTD_decompress() only needs an upper bound of decompressed size.
109 (For example, data could be necessarily cut into blocks <= 16 KB).
110 note 3 : decompressed size is always present when compression is completed using single-pass functions,
111 such as ZSTD_compress(), ZSTD_compressCCtx() ZSTD_compress_usingDict() or ZSTD_compress_usingCDict().
112 note 4 : decompressed size can be very large (64-bits value),
113 potentially larger than what local system can handle as a single memory segment.
114 In which case, it's necessary to use streaming mode to decompress data.
115 note 5 : If source is untrusted, decompressed size could be wrong or intentionally modified.
116 Always ensure return value fits within application's authorized limits.
117 Each application can set its own limits.
118 note 6 : This function replaces ZSTD_getDecompressedSize()
121 <pre><b>unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
122 </b><p> NOTE: This function is now obsolete, in favor of ZSTD_getFrameContentSize().
123 Both functions work the same way, but ZSTD_getDecompressedSize() blends
124 "empty", "unknown" and "error" results to the same return value (0),
125 while ZSTD_getFrameContentSize() gives them separate return values.
126 @return : decompressed size of `src` frame content _if known and not empty_, 0 otherwise.
129 <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>
130 size_t ZSTD_compressBound(size_t srcSize); </b>/*!< maximum compressed size in worst case single-pass scenario */<b>
131 unsigned ZSTD_isError(size_t code); </b>/*!< tells if a `size_t` function result is an error code */<b>
132 const char* ZSTD_getErrorName(size_t code); </b>/*!< provides readable string from an error code */<b>
133 int ZSTD_maxCLevel(void); </b>/*!< maximum compression level available */<b>
135 <a name="Chapter5"></a><h2>Explicit context</h2><pre></pre>
137 <h3>Compression context</h3><pre> When compressing many times,
138 it is recommended to allocate a context just once, and re-use it for each successive compression operation.
139 This will make workload friendlier for system's memory.
140 Use one context per thread for parallel execution in multi-threaded environments.
141 </pre><b><pre>typedef struct ZSTD_CCtx_s ZSTD_CCtx;
142 ZSTD_CCtx* ZSTD_createCCtx(void);
143 size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx);
145 <pre><b>size_t ZSTD_compressCCtx(ZSTD_CCtx* cctx,
146 void* dst, size_t dstCapacity,
147 const void* src, size_t srcSize,
148 int compressionLevel);
149 </b><p> Same as ZSTD_compress(), using an explicit ZSTD_CCtx
150 The function will compress at requested compression level,
151 ignoring any other parameter
154 <h3>Decompression context</h3><pre> When decompressing many times,
155 it is recommended to allocate a context only once,
156 and re-use it for each successive compression operation.
157 This will make workload friendlier for system's memory.
158 Use one context per thread for parallel execution.
159 </pre><b><pre>typedef struct ZSTD_DCtx_s ZSTD_DCtx;
160 ZSTD_DCtx* ZSTD_createDCtx(void);
161 size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx);
163 <pre><b>size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx,
164 void* dst, size_t dstCapacity,
165 const void* src, size_t srcSize);
166 </b><p> Same as ZSTD_decompress(),
167 requires an allocated ZSTD_DCtx.
168 Compatible with sticky parameters.
172 <a name="Chapter6"></a><h2>Simple dictionary API</h2><pre></pre>
174 <pre><b>size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx,
175 void* dst, size_t dstCapacity,
176 const void* src, size_t srcSize,
177 const void* dict,size_t dictSize,
178 int compressionLevel);
179 </b><p> Compression at an explicit compression level using a Dictionary.
180 A dictionary can be any arbitrary data segment (also called a prefix),
181 or a buffer with specified information (see dictBuilder/zdict.h).
182 Note : This function loads the dictionary, resulting in significant startup delay.
183 It's intended for a dictionary used only once.
184 Note 2 : When `dict == NULL || dictSize < 8` no dictionary is used.
187 <pre><b>size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx,
188 void* dst, size_t dstCapacity,
189 const void* src, size_t srcSize,
190 const void* dict,size_t dictSize);
191 </b><p> Decompression using a known Dictionary.
192 Dictionary must be identical to the one used during compression.
193 Note : This function loads the dictionary, resulting in significant startup delay.
194 It's intended for a dictionary used only once.
195 Note : When `dict == NULL || dictSize < 8` no dictionary is used.
198 <a name="Chapter7"></a><h2>Bulk processing dictionary API</h2><pre></pre>
200 <pre><b>ZSTD_CDict* ZSTD_createCDict(const void* dictBuffer, size_t dictSize,
201 int compressionLevel);
202 </b><p> When compressing multiple messages / blocks using the same dictionary, it's recommended to load it only once.
203 ZSTD_createCDict() will create a digested dictionary, ready to start future compression operations without startup cost.
204 ZSTD_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only.
205 `dictBuffer` can be released after ZSTD_CDict creation, because its content is copied within CDict.
206 Consider experimental function `ZSTD_createCDict_byReference()` if you prefer to not duplicate `dictBuffer` content.
207 Note : A ZSTD_CDict can be created from an empty dictBuffer, but it is inefficient when used to compress small data.
210 <pre><b>size_t ZSTD_freeCDict(ZSTD_CDict* CDict);
211 </b><p> Function frees memory allocated by ZSTD_createCDict().
214 <pre><b>size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx,
215 void* dst, size_t dstCapacity,
216 const void* src, size_t srcSize,
217 const ZSTD_CDict* cdict);
218 </b><p> Compression using a digested Dictionary.
219 Recommended when same dictionary is used multiple times.
220 Note : compression level is _decided at dictionary creation time_,
221 and frame parameters are hardcoded (dictID=yes, contentSize=yes, checksum=no)
224 <pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dictBuffer, size_t dictSize);
225 </b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
226 dictBuffer can be released after DDict creation, as its content is copied inside DDict.
229 <pre><b>size_t ZSTD_freeDDict(ZSTD_DDict* ddict);
230 </b><p> Function frees memory allocated with ZSTD_createDDict()
233 <pre><b>size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
234 void* dst, size_t dstCapacity,
235 const void* src, size_t srcSize,
236 const ZSTD_DDict* ddict);
237 </b><p> Decompression using a digested Dictionary.
238 Recommended when same dictionary is used multiple times.
241 <a name="Chapter8"></a><h2>Streaming</h2><pre></pre>
243 <pre><b>typedef struct ZSTD_inBuffer_s {
244 const void* src; </b>/**< start of input buffer */<b>
245 size_t size; </b>/**< size of input buffer */<b>
246 size_t pos; </b>/**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
249 <pre><b>typedef struct ZSTD_outBuffer_s {
250 void* dst; </b>/**< start of output buffer */<b>
251 size_t size; </b>/**< size of output buffer */<b>
252 size_t pos; </b>/**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
255 <a name="Chapter9"></a><h2>Streaming compression - HowTo</h2><pre>
256 A ZSTD_CStream object is required to track streaming operation.
257 Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources.
258 ZSTD_CStream objects can be reused multiple times on consecutive compression operations.
259 It is recommended to re-use ZSTD_CStream since it will play nicer with system's memory, by re-using already allocated memory.
261 For parallel execution, use one separate ZSTD_CStream per thread.
263 note : since v1.3.0, ZSTD_CStream and ZSTD_CCtx are the same thing.
265 Parameters are sticky : when starting a new compression on the same context,
266 it will re-use the same sticky parameters as previous compression session.
267 When in doubt, it's recommended to fully initialize the context before usage.
268 Use ZSTD_initCStream() to set the parameter to a selected compression level.
269 Use advanced API (ZSTD_CCtx_setParameter(), etc.) to set more specific parameters.
271 Use ZSTD_compressStream() as many times as necessary to consume input stream.
272 The function will automatically update both `pos` fields within `input` and `output`.
273 Note that the function may not consume the entire input,
274 for example, because the output buffer is already full,
275 in which case `input.pos < input.size`.
276 The caller must check if input has been entirely consumed.
277 If not, the caller must make some room to receive more compressed data,
278 and then present again remaining input data.
279 @return : a size hint, preferred nb of bytes to use as input for next function call
280 or an error code, which can be tested using ZSTD_isError().
281 Note 1 : it's just a hint, to help latency a little, any value will work fine.
282 Note 2 : size hint is guaranteed to be <= ZSTD_CStreamInSize()
284 At any moment, it's possible to flush whatever data might remain stuck within internal buffer,
285 using ZSTD_flushStream(). `output->pos` will be updated.
286 Note that, if `output->size` is too small, a single invocation of ZSTD_flushStream() might not be enough (return code > 0).
287 In which case, make some room to receive more compressed data, and call again ZSTD_flushStream().
288 @return : 0 if internal buffers are entirely flushed,
289 >0 if some data still present within internal buffer (the value is minimal estimation of remaining size),
290 or an error code, which can be tested using ZSTD_isError().
292 ZSTD_endStream() instructs to finish a frame.
293 It will perform a flush and write frame epilogue.
294 The epilogue is required for decoders to consider a frame completed.
295 flush() operation is the same, and follows same rules as ZSTD_flushStream().
296 @return : 0 if frame fully completed and fully flushed,
297 >0 if some data still present within internal buffer (the value is minimal estimation of remaining size),
298 or an error code, which can be tested using ZSTD_isError().
303 <pre><b>typedef ZSTD_CCtx ZSTD_CStream; </b>/**< CCtx and CStream are now effectively same object (>= v1.3.0) */<b>
305 <h3>ZSTD_CStream management functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream(void);
306 size_t ZSTD_freeCStream(ZSTD_CStream* zcs);
308 <h3>Streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel);
309 size_t ZSTD_compressStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
310 size_t ZSTD_flushStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
311 size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
313 <pre><b>size_t ZSTD_CStreamInSize(void); </b>/**< recommended size for input buffer */<b>
315 <pre><b>size_t ZSTD_CStreamOutSize(void); </b>/**< recommended size for output buffer. Guarantee to successfully flush at least one complete compressed block in all circumstances. */<b>
317 <a name="Chapter10"></a><h2>Streaming decompression - HowTo</h2><pre>
318 A ZSTD_DStream object is required to track streaming operations.
319 Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources.
320 ZSTD_DStream objects can be re-used multiple times.
322 Use ZSTD_initDStream() to start a new decompression operation.
323 @return : recommended first input size
324 Alternatively, use advanced API to set specific properties.
326 Use ZSTD_decompressStream() repetitively to consume your input.
327 The function will update both `pos` fields.
328 If `input.pos < input.size`, some input has not been consumed.
329 It's up to the caller to present again remaining data.
330 The function tries to flush all data decoded immediately, respecting output buffer size.
331 If `output.pos < output.size`, decoder has flushed everything it could.
332 But if `output.pos == output.size`, there might be some data left within internal buffers.,
333 In which case, call ZSTD_decompressStream() again to flush whatever remains in the buffer.
334 Note : with no additional input provided, amount of data flushed is necessarily <= ZSTD_BLOCKSIZE_MAX.
335 @return : 0 when a frame is completely decoded and fully flushed,
336 or an error code, which can be tested using ZSTD_isError(),
337 or any other value > 0, which means there is still some decoding or flushing to do to complete current frame :
338 the return value is a suggested next input size (just a hint for better latency)
339 that will never request more than the remaining frame size.
343 <pre><b>typedef ZSTD_DCtx ZSTD_DStream; </b>/**< DCtx and DStream are now effectively same object (>= v1.3.0) */<b>
345 <h3>ZSTD_DStream management functions</h3><pre></pre><b><pre>ZSTD_DStream* ZSTD_createDStream(void);
346 size_t ZSTD_freeDStream(ZSTD_DStream* zds);
348 <h3>Streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_initDStream(ZSTD_DStream* zds);
349 size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
351 <pre><b>size_t ZSTD_DStreamInSize(void); </b>/*!< recommended size for input buffer */<b>
353 <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>
355 <a name="Chapter11"></a><h2>ADVANCED AND EXPERIMENTAL FUNCTIONS</h2><pre>
356 The definitions in the following section are considered experimental.
357 They are provided for advanced scenarios.
358 They should never be used with a dynamic library, as prototypes may change in the future.
359 Use them only in association with static linking.
363 <a name="Chapter12"></a><h2>Candidate API for promotion to stable status</h2><pre>
364 The following symbols and constants form the "staging area" :
365 they are considered to join "stable API" by v1.4.0.
366 The proposal is written so that it can be made stable "as is",
367 though it's still possible to suggest improvements.
368 Staging is in fact last chance for changes,
369 the API is locked once reaching "stable" status.
373 <pre><b>int ZSTD_minCLevel(void); </b>/*!< minimum negative compression level allowed */<b>
375 <pre><b>size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize);
376 </b><p> `src` should point to the start of a ZSTD frame or skippable frame.
377 `srcSize` must be >= first frame size
378 @return : the compressed size of the first frame starting at `src`,
379 suitable to pass as `srcSize` to `ZSTD_decompress` or similar,
380 or an error code if input is invalid
383 <pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
384 size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);
385 size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs);
386 size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds);
387 size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
388 size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
389 </b><p> These functions give the _current_ memory usage of selected object.
390 Note that object memory usage can evolve (increase or decrease) over time.
393 <a name="Chapter13"></a><h2>Advanced compression API</h2><pre></pre>
395 <pre><b>typedef enum { ZSTD_fast=1,
404 </b>/* note : new strategies _might_ be added in the future.<b>
405 Only the order (from fast to strong) is guaranteed */
408 <pre><b>typedef enum {
410 </b>/* compression parameters */<b>
411 ZSTD_c_compressionLevel=100, </b>/* Update all compression parameters according to pre-defined cLevel table<b>
412 * Default level is ZSTD_CLEVEL_DEFAULT==3.
413 * Special: value 0 means default, which is controlled by ZSTD_CLEVEL_DEFAULT.
414 * Note 1 : it's possible to pass a negative compression level.
415 * Note 2 : setting a level sets all default values of other compression parameters */
416 ZSTD_c_windowLog=101, </b>/* Maximum allowed back-reference distance, expressed as power of 2.<b>
417 * Must be clamped between ZSTD_WINDOWLOG_MIN and ZSTD_WINDOWLOG_MAX.
418 * Special: value 0 means "use default windowLog".
419 * Note: Using a windowLog greater than ZSTD_WINDOWLOG_LIMIT_DEFAULT
420 * requires explicitly allowing such window size at decompression stage if using streaming. */
421 ZSTD_c_hashLog=102, </b>/* Size of the initial probe table, as a power of 2.<b>
422 * Resulting memory usage is (1 << (hashLog+2)).
423 * Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX.
424 * Larger tables improve compression ratio of strategies <= dFast,
425 * and improve speed of strategies > dFast.
426 * Special: value 0 means "use default hashLog". */
427 ZSTD_c_chainLog=103, </b>/* Size of the multi-probe search table, as a power of 2.<b>
428 * Resulting memory usage is (1 << (chainLog+2)).
429 * Must be clamped between ZSTD_CHAINLOG_MIN and ZSTD_CHAINLOG_MAX.
430 * Larger tables result in better and slower compression.
431 * This parameter is useless when using "fast" strategy.
432 * It's still useful when using "dfast" strategy,
433 * in which case it defines a secondary probe table.
434 * Special: value 0 means "use default chainLog". */
435 ZSTD_c_searchLog=104, </b>/* Number of search attempts, as a power of 2.<b>
436 * More attempts result in better and slower compression.
437 * This parameter is useless when using "fast" and "dFast" strategies.
438 * Special: value 0 means "use default searchLog". */
439 ZSTD_c_minMatch=105, </b>/* Minimum size of searched matches.<b>
440 * Note that Zstandard can still find matches of smaller size,
441 * it just tweaks its search algorithm to look for this size and larger.
442 * Larger values increase compression and decompression speed, but decrease ratio.
443 * Must be clamped between ZSTD_MINMATCH_MIN and ZSTD_MINMATCH_MAX.
444 * Note that currently, for all strategies < btopt, effective minimum is 4.
445 * , for all strategies > fast, effective maximum is 6.
446 * Special: value 0 means "use default minMatchLength". */
447 ZSTD_c_targetLength=106, </b>/* Impact of this field depends on strategy.<b>
448 * For strategies btopt, btultra & btultra2:
449 * Length of Match considered "good enough" to stop search.
450 * Larger values make compression stronger, and slower.
452 * Distance between match sampling.
453 * Larger values make compression faster, and weaker.
454 * Special: value 0 means "use default targetLength". */
455 ZSTD_c_strategy=107, </b>/* See ZSTD_strategy enum definition.<b>
456 * The higher the value of selected strategy, the more complex it is,
457 * resulting in stronger and slower compression.
458 * Special: value 0 means "use default strategy". */
460 </b>/* LDM mode parameters */<b>
461 ZSTD_c_enableLongDistanceMatching=160, </b>/* Enable long distance matching.<b>
462 * This parameter is designed to improve compression ratio
463 * for large inputs, by finding large matches at long distance.
464 * It increases memory usage and window size.
465 * Note: enabling this parameter increases default ZSTD_c_windowLog to 128 MB
466 * except when expressly set to a different value. */
467 ZSTD_c_ldmHashLog=161, </b>/* Size of the table for long distance matching, as a power of 2.<b>
468 * Larger values increase memory usage and compression ratio,
469 * but decrease compression speed.
470 * Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX
471 * default: windowlog - 7.
472 * Special: value 0 means "automatically determine hashlog". */
473 ZSTD_c_ldmMinMatch=162, </b>/* Minimum match size for long distance matcher.<b>
474 * Larger/too small values usually decrease compression ratio.
475 * Must be clamped between ZSTD_LDM_MINMATCH_MIN and ZSTD_LDM_MINMATCH_MAX.
476 * Special: value 0 means "use default value" (default: 64). */
477 ZSTD_c_ldmBucketSizeLog=163, </b>/* Log size of each bucket in the LDM hash table for collision resolution.<b>
478 * Larger values improve collision resolution but decrease compression speed.
479 * The maximum value is ZSTD_LDM_BUCKETSIZELOG_MAX.
480 * Special: value 0 means "use default value" (default: 3). */
481 ZSTD_c_ldmHashRateLog=164, </b>/* Frequency of inserting/looking up entries into the LDM hash table.<b>
482 * Must be clamped between 0 and (ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN).
483 * Default is MAX(0, (windowLog - ldmHashLog)), optimizing hash table usage.
484 * Larger values improve compression speed.
485 * Deviating far from default value will likely result in a compression ratio decrease.
486 * Special: value 0 means "automatically determine hashRateLog". */
488 </b>/* frame parameters */<b>
489 ZSTD_c_contentSizeFlag=200, </b>/* Content size will be written into frame header _whenever known_ (default:1)<b>
490 * Content size must be known at the beginning of compression.
491 * This is automatically the case when using ZSTD_compress2(),
492 * For streaming variants, content size must be provided with ZSTD_CCtx_setPledgedSrcSize() */
493 ZSTD_c_checksumFlag=201, </b>/* A 32-bits checksum of content is written at end of frame (default:0) */<b>
494 ZSTD_c_dictIDFlag=202, </b>/* When applicable, dictionary's ID is written into frame header (default:1) */<b>
496 </b>/* multi-threading parameters */<b>
497 </b>/* These parameters are only useful if multi-threading is enabled (compiled with build macro ZSTD_MULTITHREAD).<b>
498 * They return an error otherwise. */
499 ZSTD_c_nbWorkers=400, </b>/* Select how many threads will be spawned to compress in parallel.<b>
500 * When nbWorkers >= 1, triggers asynchronous mode when used with ZSTD_compressStream*() :
501 * ZSTD_compressStream*() consumes input and flush output if possible, but immediately gives back control to caller,
502 * while compression work is performed in parallel, within worker threads.
503 * (note : a strong exception to this rule is when first invocation of ZSTD_compressStream2() sets ZSTD_e_end :
504 * in which case, ZSTD_compressStream2() delegates to ZSTD_compress2(), which is always a blocking call).
505 * More workers improve speed, but also increase memory usage.
506 * Default value is `0`, aka "single-threaded mode" : no worker is spawned, compression is performed inside Caller's thread, all invocations are blocking */
507 ZSTD_c_jobSize=401, </b>/* Size of a compression job. This value is enforced only when nbWorkers >= 1.<b>
508 * Each compression job is completed in parallel, so this value can indirectly impact the nb of active threads.
509 * 0 means default, which is dynamically determined based on compression parameters.
510 * Job size must be a minimum of overlap size, or 1 MB, whichever is largest.
511 * The minimum size is automatically and transparently enforced */
512 ZSTD_c_overlapLog=402, </b>/* Control the overlap size, as a fraction of window size.<b>
513 * The overlap size is an amount of data reloaded from previous job at the beginning of a new job.
514 * It helps preserve compression ratio, while each job is compressed in parallel.
515 * This value is enforced only when nbWorkers >= 1.
516 * Larger values increase compression ratio, but decrease speed.
517 * Possible values range from 0 to 9 :
518 * - 0 means "default" : value will be determined by the library, depending on strategy
519 * - 1 means "no overlap"
520 * - 9 means "full overlap", using a full window size.
521 * Each intermediate rank increases/decreases load size by a factor 2 :
522 * 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
523 * default value varies between 6 and 9, depending on strategy */
525 </b>/* note : additional experimental parameters are also available<b>
526 * within the experimental section of the API.
527 * At the time of this writing, they include :
530 * ZSTD_c_forceMaxWindow
531 * ZSTD_c_forceAttachDict
532 * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them.
533 * note : never ever use experimentalParam? names directly;
534 * also, the enums values themselves are unstable and can still change.
536 ZSTD_c_experimentalParam1=500,
537 ZSTD_c_experimentalParam2=10,
538 ZSTD_c_experimentalParam3=1000,
539 ZSTD_c_experimentalParam4=1001
542 <pre><b>typedef struct {
548 <pre><b>ZSTD_bounds ZSTD_cParam_getBounds(ZSTD_cParameter cParam);
549 </b><p> All parameters must belong to an interval with lower and upper bounds,
550 otherwise they will either trigger an error or be automatically clamped.
551 @return : a structure, ZSTD_bounds, which contains
552 - an error status field, which must be tested using ZSTD_isError()
553 - lower and upper bounds, both inclusive
557 <pre><b>size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int value);
558 </b><p> Set one compression parameter, selected by enum ZSTD_cParameter.
559 All parameters have valid bounds. Bounds can be queried using ZSTD_cParam_getBounds().
560 Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter).
561 Setting a parameter is generally only possible during frame initialization (before starting compression).
562 Exception : when using multi-threading mode (nbWorkers >= 1),
563 the following parameters can be updated _during_ compression (within same frame):
564 => compressionLevel, hashLog, chainLog, searchLog, minMatch, targetLength and strategy.
565 new parameters will be active for next job only (after a flush()).
566 @return : an error code (which can be tested using ZSTD_isError()).
570 <pre><b>size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize);
571 </b><p> Total input data size to be compressed as a single frame.
572 Value will be written in frame header, unless if explicitly forbidden using ZSTD_c_contentSizeFlag.
573 This value will also be controlled at end of frame, and trigger an error if not respected.
574 @result : 0, or an error code (which can be tested with ZSTD_isError()).
575 Note 1 : pledgedSrcSize==0 actually means zero, aka an empty frame.
576 In order to mean "unknown content size", pass constant ZSTD_CONTENTSIZE_UNKNOWN.
577 ZSTD_CONTENTSIZE_UNKNOWN is default value for any new frame.
578 Note 2 : pledgedSrcSize is only valid once, for the next frame.
579 It's discarded at the end of the frame, and replaced by ZSTD_CONTENTSIZE_UNKNOWN.
580 Note 3 : Whenever all input data is provided and consumed in a single round,
581 for example with ZSTD_compress2(),
582 or invoking immediately ZSTD_compressStream2(,,,ZSTD_e_end),
583 this value is automatically overriden by srcSize instead.
587 <pre><b>size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize);
588 </b><p> Create an internal CDict from `dict` buffer.
589 Decompression will have to use same dictionary.
590 @result : 0, or an error code (which can be tested with ZSTD_isError()).
591 Special: Loading a NULL (or 0-size) dictionary invalidates previous dictionary,
592 meaning "return to no-dictionary mode".
593 Note 1 : Dictionary is sticky, it will be used for all future compressed frames.
594 To return to "no-dictionary" situation, load a NULL dictionary (or reset parameters).
595 Note 2 : Loading a dictionary involves building tables.
596 It's also a CPU consuming operation, with non-negligible impact on latency.
597 Tables are dependent on compression parameters, and for this reason,
598 compression parameters can no longer be changed after loading a dictionary.
599 Note 3 :`dict` content will be copied internally.
600 Use experimental ZSTD_CCtx_loadDictionary_byReference() to reference content instead.
601 In such a case, dictionary buffer must outlive its users.
602 Note 4 : Use ZSTD_CCtx_loadDictionary_advanced()
603 to precisely select how dictionary content must be interpreted.
606 <pre><b>size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict);
607 </b><p> Reference a prepared dictionary, to be used for all next compressed frames.
608 Note that compression parameters are enforced from within CDict,
609 and supercede any compression parameter previously set within CCtx.
610 The dictionary will remain valid for future compressed frames using same CCtx.
611 @result : 0, or an error code (which can be tested with ZSTD_isError()).
612 Special : Referencing a NULL CDict means "return to no-dictionary mode".
613 Note 1 : Currently, only one dictionary can be managed.
614 Referencing a new dictionary effectively "discards" any previous one.
615 Note 2 : CDict is just referenced, its lifetime must outlive its usage within CCtx.
618 <pre><b>size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx,
619 const void* prefix, size_t prefixSize);
620 </b><p> Reference a prefix (single-usage dictionary) for next compressed frame.
621 A prefix is **only used once**. Tables are discarded at end of frame (ZSTD_e_end).
622 Decompression will need same prefix to properly regenerate data.
623 Compressing with a prefix is similar in outcome as performing a diff and compressing it,
624 but performs much faster, especially during decompression (compression speed is tunable with compression level).
625 @result : 0, or an error code (which can be tested with ZSTD_isError()).
626 Special: Adding any prefix (including NULL) invalidates any previous prefix or dictionary
627 Note 1 : Prefix buffer is referenced. It **must** outlive compression.
628 Its content must remain unmodified during compression.
629 Note 2 : If the intention is to diff some large src data blob with some prior version of itself,
630 ensure that the window size is large enough to contain the entire source.
631 See ZSTD_c_windowLog.
632 Note 3 : Referencing a prefix involves building tables, which are dependent on compression parameters.
633 It's a CPU consuming operation, with non-negligible impact on latency.
634 If there is a need to use the same prefix multiple times, consider loadDictionary instead.
635 Note 4 : By default, the prefix is interpreted as raw content (ZSTD_dm_rawContent).
636 Use experimental ZSTD_CCtx_refPrefix_advanced() to alter dictionary interpretation.
639 <pre><b>typedef enum {
640 ZSTD_reset_session_only = 1,
641 ZSTD_reset_parameters = 2,
642 ZSTD_reset_session_and_parameters = 3
643 } ZSTD_ResetDirective;
645 <pre><b>size_t ZSTD_CCtx_reset(ZSTD_CCtx* cctx, ZSTD_ResetDirective reset);
646 </b><p> There are 2 different things that can be reset, independently or jointly :
647 - The session : will stop compressing current frame, and make CCtx ready to start a new one.
648 Useful after an error, or to interrupt any ongoing compression.
649 Any internal data not yet flushed is cancelled.
650 Compression parameters and dictionary remain unchanged.
651 They will be used to compress next frame.
652 Resetting session never fails.
653 - The parameters : changes all parameters back to "default".
654 This removes any reference to any dictionary too.
655 Parameters can only be changed between 2 sessions (i.e. no compression is currently ongoing)
656 otherwise the reset fails, and function returns an error value (which can be tested using ZSTD_isError())
657 - Both : similar to resetting the session, followed by resetting parameters.
661 <pre><b>size_t ZSTD_compress2( ZSTD_CCtx* cctx,
662 void* dst, size_t dstCapacity,
663 const void* src, size_t srcSize);
664 </b><p> Behave the same as ZSTD_compressCCtx(), but compression parameters are set using the advanced API.
665 ZSTD_compress2() always starts a new frame.
666 Should cctx hold data from a previously unfinished frame, everything about it is forgotten.
667 - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*()
668 - The function is always blocking, returns when compression is completed.
669 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
670 @return : compressed size written into `dst` (<= `dstCapacity),
671 or an error code if it fails (which can be tested using ZSTD_isError()).
675 <pre><b>typedef enum {
676 ZSTD_e_continue=0, </b>/* collect more data, encoder decides when to output compressed result, for optimal compression ratio */<b>
677 ZSTD_e_flush=1, </b>/* flush any data provided so far,<b>
678 * it creates (at least) one new block, that can be decoded immediately on reception;
679 * frame will continue: any future data can still reference previously compressed data, improving compression. */
680 ZSTD_e_end=2 </b>/* flush any remaining data _and_ close current frame.<b>
681 * note that frame is only closed after compressed data is fully flushed (return value == 0).
682 * After that point, any additional data starts a new frame.
683 * note : each frame is independent (does not reference any content from previous frame). */
686 <pre><b>size_t ZSTD_compressStream2( ZSTD_CCtx* cctx,
687 ZSTD_outBuffer* output,
688 ZSTD_inBuffer* input,
689 ZSTD_EndDirective endOp);
690 </b><p> Behaves about the same as ZSTD_compressStream, with additional control on end directive.
691 - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*()
692 - Compression parameters cannot be changed once compression is started (save a list of exceptions in multi-threading mode)
693 - outpot->pos must be <= dstCapacity, input->pos must be <= srcSize
694 - outpot->pos and input->pos will be updated. They are guaranteed to remain below their respective limit.
695 - When nbWorkers==0 (default), function is blocking : it completes its job before returning to caller.
696 - When nbWorkers>=1, function is non-blocking : it just acquires a copy of input, and distributes jobs to internal worker threads, flush whatever is available,
697 and then immediately returns, just indicating that there is some data remaining to be flushed.
698 The function nonetheless guarantees forward progress : it will return only after it reads or write at least 1+ byte.
699 - 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.
700 - @return provides a minimum amount of data remaining to be flushed from internal buffers
701 or an error code, which can be tested using ZSTD_isError().
702 if @return != 0, flush is not fully completed, there is still some data left within internal buffers.
703 This is useful for ZSTD_e_flush, since in this case more flushes are necessary to empty all buffers.
704 For ZSTD_e_end, @return == 0 when internal buffers are fully flushed and frame is completed.
705 - after a ZSTD_e_end directive, if internal buffer is not fully flushed (@return != 0),
706 only ZSTD_e_end or ZSTD_e_flush operations are allowed.
707 Before starting a new compression job, or changing compression parameters,
708 it is required to fully flush internal buffers.
712 <pre><b>typedef enum {
714 ZSTD_d_windowLogMax=100, </b>/* Select a size limit (in power of 2) beyond which<b>
715 * the streaming API will refuse to allocate memory buffer
716 * in order to protect the host from unreasonable memory requirements.
717 * This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode.
718 * By default, a decompression context accepts window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT) */
720 </b>/* note : additional experimental parameters are also available<b>
721 * within the experimental section of the API.
722 * At the time of this writing, they include :
724 * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them.
725 * note : never ever use experimentalParam? names directly
727 ZSTD_d_experimentalParam1=1000
731 <pre><b>ZSTD_bounds ZSTD_dParam_getBounds(ZSTD_dParameter dParam);
732 </b><p> All parameters must belong to an interval with lower and upper bounds,
733 otherwise they will either trigger an error or be automatically clamped.
734 @return : a structure, ZSTD_bounds, which contains
735 - an error status field, which must be tested using ZSTD_isError()
736 - both lower and upper bounds, inclusive
740 <pre><b>size_t ZSTD_DCtx_setParameter(ZSTD_DCtx* dctx, ZSTD_dParameter param, int value);
741 </b><p> Set one compression parameter, selected by enum ZSTD_dParameter.
742 All parameters have valid bounds. Bounds can be queried using ZSTD_dParam_getBounds().
743 Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter).
744 Setting a parameter is only possible during frame initialization (before starting decompression).
745 @return : 0, or an error code (which can be tested using ZSTD_isError()).
749 <pre><b>size_t ZSTD_DCtx_loadDictionary(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
750 </b><p> Create an internal DDict from dict buffer,
751 to be used to decompress next frames.
752 The dictionary remains valid for all future frames, until explicitly invalidated.
753 @result : 0, or an error code (which can be tested with ZSTD_isError()).
754 Special : Adding a NULL (or 0-size) dictionary invalidates any previous dictionary,
755 meaning "return to no-dictionary mode".
756 Note 1 : Loading a dictionary involves building tables,
757 which has a non-negligible impact on CPU usage and latency.
758 It's recommended to "load once, use many times", to amortize the cost
759 Note 2 :`dict` content will be copied internally, so `dict` can be released after loading.
760 Use ZSTD_DCtx_loadDictionary_byReference() to reference dictionary content instead.
761 Note 3 : Use ZSTD_DCtx_loadDictionary_advanced() to take control of
762 how dictionary content is loaded and interpreted.
766 <pre><b>size_t ZSTD_DCtx_refDDict(ZSTD_DCtx* dctx, const ZSTD_DDict* ddict);
767 </b><p> Reference a prepared dictionary, to be used to decompress next frames.
768 The dictionary remains active for decompression of future frames using same DCtx.
769 @result : 0, or an error code (which can be tested with ZSTD_isError()).
770 Note 1 : Currently, only one dictionary can be managed.
771 Referencing a new dictionary effectively "discards" any previous one.
772 Special: referencing a NULL DDict means "return to no-dictionary mode".
773 Note 2 : DDict is just referenced, its lifetime must outlive its usage from DCtx.
777 <pre><b>size_t ZSTD_DCtx_refPrefix(ZSTD_DCtx* dctx,
778 const void* prefix, size_t prefixSize);
779 </b><p> Reference a prefix (single-usage dictionary) to decompress next frame.
780 This is the reverse operation of ZSTD_CCtx_refPrefix(),
781 and must use the same prefix as the one used during compression.
782 Prefix is **only used once**. Reference is discarded at end of frame.
783 End of frame is reached when ZSTD_decompressStream() returns 0.
784 @result : 0, or an error code (which can be tested with ZSTD_isError()).
785 Note 1 : Adding any prefix (including NULL) invalidates any previously set prefix or dictionary
786 Note 2 : Prefix buffer is referenced. It **must** outlive decompression.
787 Prefix buffer must remain unmodified up to the end of frame,
788 reached when ZSTD_decompressStream() returns 0.
789 Note 3 : By default, the prefix is treated as raw content (ZSTD_dm_rawContent).
790 Use ZSTD_CCtx_refPrefix_advanced() to alter dictMode (Experimental section)
791 Note 4 : Referencing a raw content prefix has almost no cpu nor memory cost.
792 A full dictionary is more costly, as it requires building tables.
796 <pre><b>size_t ZSTD_DCtx_reset(ZSTD_DCtx* dctx, ZSTD_ResetDirective reset);
797 </b><p> Return a DCtx to clean state.
798 Session and parameters can be reset jointly or separately.
799 Parameters can only be reset when no active frame is being decompressed.
800 @return : 0, or an error code, which can be tested with ZSTD_isError()
804 <a name="Chapter14"></a><h2>experimental API (static linking only)</h2><pre>
805 The following symbols and constants
806 are not planned to join "stable API" status in the near future.
807 They can still change in future versions.
808 Some of them are planned to remain in the static_only section indefinitely.
809 Some of them might be removed in the future (especially when redundant with existing stable functions)
813 <pre><b>typedef struct {
814 unsigned windowLog; </b>/**< largest match distance : larger == more compression, more memory needed during decompression */<b>
815 unsigned chainLog; </b>/**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */<b>
816 unsigned hashLog; </b>/**< dispatch table : larger == faster, more memory */<b>
817 unsigned searchLog; </b>/**< nb of searches : larger == more compression, slower */<b>
818 unsigned minMatch; </b>/**< match length searched : larger == faster decompression, sometimes less compression */<b>
819 unsigned targetLength; </b>/**< acceptable match size for optimal parser (only) : larger == more compression, slower */<b>
820 ZSTD_strategy strategy; </b>/**< see ZSTD_strategy definition above */<b>
821 } ZSTD_compressionParameters;
823 <pre><b>typedef struct {
824 int contentSizeFlag; </b>/**< 1: content size will be in frame header (when known) */<b>
825 int checksumFlag; </b>/**< 1: generate a 32-bits checksum using XXH64 algorithm at end of frame, for error detection */<b>
826 int noDictIDFlag; </b>/**< 1: no dictID will be saved into frame header (dictID is only useful for dictionary compression) */<b>
827 } ZSTD_frameParameters;
829 <pre><b>typedef struct {
830 ZSTD_compressionParameters cParams;
831 ZSTD_frameParameters fParams;
834 <pre><b>typedef enum {
835 ZSTD_dct_auto = 0, </b>/* dictionary is "full" when starting with ZSTD_MAGIC_DICTIONARY, otherwise it is "rawContent" */<b>
836 ZSTD_dct_rawContent = 1, </b>/* ensures dictionary is always loaded as rawContent, even if it starts with ZSTD_MAGIC_DICTIONARY */<b>
837 ZSTD_dct_fullDict = 2 </b>/* refuses to load a dictionary if it does not respect Zstandard's specification, starting with ZSTD_MAGIC_DICTIONARY */<b>
838 } ZSTD_dictContentType_e;
840 <pre><b>typedef enum {
841 ZSTD_dlm_byCopy = 0, </b>/**< Copy dictionary content internally */<b>
842 ZSTD_dlm_byRef = 1, </b>/**< Reference dictionary content -- the dictionary buffer must outlive its users. */<b>
843 } ZSTD_dictLoadMethod_e;
845 <pre><b>typedef enum {
846 </b>/* Opened question : should we have a format ZSTD_f_auto ?<b>
847 * Today, it would mean exactly the same as ZSTD_f_zstd1.
848 * But, in the future, should several formats become supported,
849 * on the compression side, it would mean "default format".
850 * On the decompression side, it would mean "automatic format detection",
851 * so that ZSTD_f_zstd1 would mean "accept *only* zstd frames".
852 * Since meaning is a little different, another option could be to define different enums for compression and decompression.
853 * This question could be kept for later, when there are actually multiple formats to support,
854 * but there is also the question of pinning enum values, and pinning value `0` is especially important */
855 ZSTD_f_zstd1 = 0, </b>/* zstd frame format, specified in zstd_compression_format.md (default) */<b>
856 ZSTD_f_zstd1_magicless = 1, </b>/* Variant of zstd frame format, without initial 4-bytes magic number.<b>
857 * Useful to save 4 bytes per generated frame.
858 * Decoder cannot recognise automatically this format, requiring this instruction. */
861 <pre><b>typedef enum {
862 </b>/* Note: this enum and the behavior it controls are effectively internal<b>
863 * implementation details of the compressor. They are expected to continue
864 * to evolve and should be considered only in the context of extremely
865 * advanced performance tuning.
867 * Zstd currently supports the use of a CDict in two ways:
869 * - The contents of the CDict can be copied into the working context. This
870 * means that the compression can search both the dictionary and input
871 * while operating on a single set of internal tables. This makes
872 * the compression faster per-byte of input. However, the initial copy of
873 * the CDict's tables incurs a fixed cost at the beginning of the
874 * compression. For small compressions (< 8 KB), that copy can dominate
875 * the cost of the compression.
877 * - The CDict's tables can be used in-place. In this model, compression is
878 * slower per input byte, because the compressor has to search two sets of
879 * tables. However, this model incurs no start-up cost (as long as the
880 * working context's tables can be reused). For small inputs, this can be
881 * faster than copying the CDict's tables.
883 * Zstd has a simple internal heuristic that selects which strategy to use
884 * at the beginning of a compression. However, if experimentation shows that
885 * Zstd is making poor choices, it is possible to override that choice with
888 ZSTD_dictDefaultAttach = 0, </b>/* Use the default heuristic. */<b>
889 ZSTD_dictForceAttach = 1, </b>/* Never copy the dictionary. */<b>
890 ZSTD_dictForceCopy = 2, </b>/* Always copy the dictionary. */<b>
891 } ZSTD_dictAttachPref_e;
893 <a name="Chapter15"></a><h2>Frame size functions</h2><pre></pre>
895 <pre><b>unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize);
896 </b><p> `src` should point the start of a series of ZSTD encoded and/or skippable frames
897 `srcSize` must be the _exact_ size of this series
898 (i.e. there should be a frame boundary exactly at `srcSize` bytes after `src`)
899 @return : - decompressed size of all data in all successive frames
900 - if the decompressed size cannot be determined: ZSTD_CONTENTSIZE_UNKNOWN
901 - if an error occurred: ZSTD_CONTENTSIZE_ERROR
903 note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
904 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size.
905 In which case, it's necessary to use streaming mode to decompress data.
906 note 2 : decompressed size is always present when compression is done with ZSTD_compress()
907 note 3 : decompressed size can be very large (64-bits value),
908 potentially larger than what local system can handle as a single memory segment.
909 In which case, it's necessary to use streaming mode to decompress data.
910 note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified.
911 Always ensure result fits within application's authorized limits.
912 Each application can set its own limits.
913 note 5 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to
914 read each contained frame header. This is fast as most of the data is skipped,
915 however it does mean that all frame data must be present and valid.
918 <pre><b>size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize);
919 </b><p> srcSize must be >= ZSTD_FRAMEHEADERSIZE_PREFIX.
920 @return : size of the Frame Header,
921 or an error code (if srcSize is too small)
924 <a name="Chapter16"></a><h2>Memory management</h2><pre></pre>
926 <pre><b>size_t ZSTD_estimateCCtxSize(int compressionLevel);
927 size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams);
928 size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params);
929 size_t ZSTD_estimateDCtxSize(void);
930 </b><p> These functions make it possible to estimate memory usage
931 of a future {D,C}Ctx, before its creation.
932 ZSTD_estimateCCtxSize() will provide a budget large enough for any compression level up to selected one.
933 It will also consider src size to be arbitrarily "large", which is worst case.
934 If srcSize is known to always be small, ZSTD_estimateCCtxSize_usingCParams() can provide a tighter estimation.
935 ZSTD_estimateCCtxSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel.
936 ZSTD_estimateCCtxSize_usingCCtxParams() can be used in tandem with ZSTD_CCtxParam_setParameter(). Only single-threaded compression is supported. This function will return an error code if ZSTD_c_nbWorkers is >= 1.
937 Note : CCtx size estimation is only correct for single-threaded compression.
940 <pre><b>size_t ZSTD_estimateCStreamSize(int compressionLevel);
941 size_t ZSTD_estimateCStreamSize_usingCParams(ZSTD_compressionParameters cParams);
942 size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params);
943 size_t ZSTD_estimateDStreamSize(size_t windowSize);
944 size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize);
945 </b><p> ZSTD_estimateCStreamSize() will provide a budget large enough for any compression level up to selected one.
946 It will also consider src size to be arbitrarily "large", which is worst case.
947 If srcSize is known to always be small, ZSTD_estimateCStreamSize_usingCParams() can provide a tighter estimation.
948 ZSTD_estimateCStreamSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel.
949 ZSTD_estimateCStreamSize_usingCCtxParams() can be used in tandem with ZSTD_CCtxParam_setParameter(). Only single-threaded compression is supported. This function will return an error code if ZSTD_c_nbWorkers is >= 1.
950 Note : CStream size estimation is only correct for single-threaded compression.
951 ZSTD_DStream memory budget depends on window Size.
952 This information can be passed manually, using ZSTD_estimateDStreamSize,
953 or deducted from a valid frame Header, using ZSTD_estimateDStreamSize_fromFrame();
954 Note : if streaming is init with function ZSTD_init?Stream_usingDict(),
955 an internal ?Dict will be created, which additional size is not estimated here.
956 In this case, get total size by adding ZSTD_estimate?DictSize
959 <pre><b>size_t ZSTD_estimateCDictSize(size_t dictSize, int compressionLevel);
960 size_t ZSTD_estimateCDictSize_advanced(size_t dictSize, ZSTD_compressionParameters cParams, ZSTD_dictLoadMethod_e dictLoadMethod);
961 size_t ZSTD_estimateDDictSize(size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod);
962 </b><p> ZSTD_estimateCDictSize() will bet that src size is relatively "small", and content is copied, like ZSTD_createCDict().
963 ZSTD_estimateCDictSize_advanced() makes it possible to control compression parameters precisely, like ZSTD_createCDict_advanced().
964 Note : dictionaries created by reference (`ZSTD_dlm_byRef`) are logically smaller.
968 <pre><b>ZSTD_CCtx* ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize);
969 ZSTD_CStream* ZSTD_initStaticCStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticCCtx() */<b>
970 </b><p> Initialize an object using a pre-allocated fixed-size buffer.
971 workspace: The memory area to emplace the object into.
972 Provided pointer *must be 8-bytes aligned*.
973 Buffer must outlive object.
974 workspaceSize: Use ZSTD_estimate*Size() to determine
975 how large workspace must be to support target scenario.
976 @return : pointer to object (same address as workspace, just different type),
977 or NULL if error (size too small, incorrect alignment, etc.)
978 Note : zstd will never resize nor malloc() when using a static buffer.
979 If the object requires more memory than available,
980 zstd will just error out (typically ZSTD_error_memory_allocation).
981 Note 2 : there is no corresponding "free" function.
982 Since workspace is allocated externally, it must be freed externally too.
983 Note 3 : cParams : use ZSTD_getCParams() to convert a compression level
984 into its associated cParams.
985 Limitation 1 : currently not compatible with internal dictionary creation, triggered by
986 ZSTD_CCtx_loadDictionary(), ZSTD_initCStream_usingDict() or ZSTD_initDStream_usingDict().
987 Limitation 2 : static cctx currently not compatible with multi-threading.
988 Limitation 3 : static dctx is incompatible with legacy support.
992 <pre><b>ZSTD_DStream* ZSTD_initStaticDStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticDCtx() */<b>
994 <pre><b>typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size);
995 typedef void (*ZSTD_freeFunction) (void* opaque, void* address);
996 typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem;
997 static ZSTD_customMem const ZSTD_defaultCMem = { NULL, NULL, NULL }; </b>/**< this constant defers to stdlib's functions */<b>
998 </b><p> These prototypes make it possible to pass your own allocation/free functions.
999 ZSTD_customMem is provided at creation time, using ZSTD_create*_advanced() variants listed below.
1000 All allocation/free operations will be completed using these custom variants instead of regular <stdlib.h> ones.
1004 <a name="Chapter17"></a><h2>Advanced compression functions</h2><pre></pre>
1006 <pre><b>ZSTD_CDict* ZSTD_createCDict_byReference(const void* dictBuffer, size_t dictSize, int compressionLevel);
1007 </b><p> Create a digested dictionary for compression
1008 Dictionary content is just referenced, not duplicated.
1009 As a consequence, `dictBuffer` **must** outlive CDict,
1010 and its content must remain unmodified throughout the lifetime of CDict.
1013 <pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
1014 </b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize.
1015 `estimatedSrcSize` value is optional, select 0 if not known
1018 <pre><b>ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
1019 </b><p> same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`.
1020 All fields of `ZSTD_frameParameters` are set to default : contentSize=1, checksum=0, noDictID=0
1023 <pre><b>size_t ZSTD_checkCParams(ZSTD_compressionParameters params);
1024 </b><p> Ensure param values remain within authorized range
1027 <pre><b>ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize);
1028 </b><p> optimize params for a given `srcSize` and `dictSize`.
1029 both values are optional, select `0` if unknown.
1032 <pre><b>size_t ZSTD_compress_advanced(ZSTD_CCtx* cctx,
1033 void* dst, size_t dstCapacity,
1034 const void* src, size_t srcSize,
1035 const void* dict,size_t dictSize,
1036 ZSTD_parameters params);
1037 </b><p> Same as ZSTD_compress_usingDict(), with fine-tune control over compression parameters (by structure)
1040 <pre><b>size_t ZSTD_compress_usingCDict_advanced(ZSTD_CCtx* cctx,
1041 void* dst, size_t dstCapacity,
1042 const void* src, size_t srcSize,
1043 const ZSTD_CDict* cdict,
1044 ZSTD_frameParameters fParams);
1045 </b><p> Same as ZSTD_compress_usingCDict(), with fine-tune control over frame parameters
1048 <pre><b>size_t ZSTD_CCtx_loadDictionary_byReference(ZSTD_CCtx* cctx, const void* dict, size_t dictSize);
1049 </b><p> Same as ZSTD_CCtx_loadDictionary(), but dictionary content is referenced, instead of being copied into CCtx.
1050 It saves some memory, but also requires that `dict` outlives its usage within `cctx`
1053 <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);
1054 </b><p> Same as ZSTD_CCtx_loadDictionary(), but gives finer control over
1055 how to load the dictionary (by copy ? by reference ?)
1056 and how to interpret it (automatic ? force raw mode ? full mode only ?)
1059 <pre><b>size_t ZSTD_CCtx_refPrefix_advanced(ZSTD_CCtx* cctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType);
1060 </b><p> Same as ZSTD_CCtx_refPrefix(), but gives finer control over
1061 how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?)
1064 <pre><b>size_t ZSTD_CCtx_getParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int* value);
1065 </b><p> Get the requested compression parameter value, selected by enum ZSTD_cParameter,
1066 and store it into int* value.
1067 @return : 0, or an error code (which can be tested with ZSTD_isError()).
1071 <pre><b>ZSTD_CCtx_params* ZSTD_createCCtxParams(void);
1072 size_t ZSTD_freeCCtxParams(ZSTD_CCtx_params* params);
1073 </b><p> Quick howto :
1074 - ZSTD_createCCtxParams() : Create a ZSTD_CCtx_params structure
1075 - ZSTD_CCtxParam_setParameter() : Push parameters one by one into
1076 an existing ZSTD_CCtx_params structure.
1078 ZSTD_CCtx_setParameter().
1079 - ZSTD_CCtx_setParametersUsingCCtxParams() : Apply parameters to
1081 These parameters will be applied to
1082 all subsequent frames.
1083 - ZSTD_compressStream2() : Do compression using the CCtx.
1084 - ZSTD_freeCCtxParams() : Free the memory.
1086 This can be used with ZSTD_estimateCCtxSize_advanced_usingCCtxParams()
1087 for static allocation of CCtx for single-threaded compression.
1091 <pre><b>size_t ZSTD_CCtxParams_reset(ZSTD_CCtx_params* params);
1092 </b><p> Reset params to default values.
1096 <pre><b>size_t ZSTD_CCtxParams_init(ZSTD_CCtx_params* cctxParams, int compressionLevel);
1097 </b><p> Initializes the compression parameters of cctxParams according to
1098 compression level. All other parameters are reset to their default values.
1102 <pre><b>size_t ZSTD_CCtxParams_init_advanced(ZSTD_CCtx_params* cctxParams, ZSTD_parameters params);
1103 </b><p> Initializes the compression and frame parameters of cctxParams according to
1104 params. All other parameters are reset to their default values.
1108 <pre><b>size_t ZSTD_CCtxParam_setParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int value);
1109 </b><p> Similar to ZSTD_CCtx_setParameter.
1110 Set one compression parameter, selected by enum ZSTD_cParameter.
1111 Parameters must be applied to a ZSTD_CCtx using ZSTD_CCtx_setParametersUsingCCtxParams().
1112 @result : 0, or an error code (which can be tested with ZSTD_isError()).
1116 <pre><b>size_t ZSTD_CCtxParam_getParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int* value);
1117 </b><p> Similar to ZSTD_CCtx_getParameter.
1118 Get the requested value of one compression parameter, selected by enum ZSTD_cParameter.
1119 @result : 0, or an error code (which can be tested with ZSTD_isError()).
1123 <pre><b>size_t ZSTD_CCtx_setParametersUsingCCtxParams(
1124 ZSTD_CCtx* cctx, const ZSTD_CCtx_params* params);
1125 </b><p> Apply a set of ZSTD_CCtx_params to the compression context.
1126 This can be done even after compression is started,
1127 if nbWorkers==0, this will have no impact until a new compression is started.
1128 if nbWorkers>=1, new parameters will be picked up at next job,
1129 with a few restrictions (windowLog, pledgedSrcSize, nbWorkers, jobSize, and overlapLog are not updated).
1133 <pre><b>size_t ZSTD_compressStream2_simpleArgs (
1135 void* dst, size_t dstCapacity, size_t* dstPos,
1136 const void* src, size_t srcSize, size_t* srcPos,
1137 ZSTD_EndDirective endOp);
1138 </b><p> Same as ZSTD_compressStream2(),
1139 but using only integral types as arguments.
1140 This variant might be helpful for binders from dynamic languages
1141 which have troubles handling structures containing memory pointers.
1145 <a name="Chapter18"></a><h2>Advanced decompression functions</h2><pre></pre>
1147 <pre><b>unsigned ZSTD_isFrame(const void* buffer, size_t size);
1148 </b><p> Tells if the content of `buffer` starts with a valid Frame Identifier.
1149 Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0.
1150 Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled.
1151 Note 3 : Skippable Frame Identifiers are considered valid.
1154 <pre><b>ZSTD_DDict* ZSTD_createDDict_byReference(const void* dictBuffer, size_t dictSize);
1155 </b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
1156 Dictionary content is referenced, and therefore stays in dictBuffer.
1157 It is important that dictBuffer outlives DDict,
1158 it must remain read accessible throughout the lifetime of DDict
1161 <pre><b>unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize);
1162 </b><p> Provides the dictID stored within dictionary.
1163 if @return == 0, the dictionary is not conformant with Zstandard specification.
1164 It can still be loaded, but as a content-only dictionary.
1167 <pre><b>unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict);
1168 </b><p> Provides the dictID of the dictionary loaded into `ddict`.
1169 If @return == 0, the dictionary is not conformant to Zstandard specification, or empty.
1170 Non-conformant dictionaries can still be loaded, but as content-only dictionaries.
1173 <pre><b>unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
1174 </b><p> Provides the dictID required to decompressed the frame stored within `src`.
1175 If @return == 0, the dictID could not be decoded.
1176 This could for one of the following reasons :
1177 - The frame does not require a dictionary to be decoded (most common case).
1178 - The frame was built with dictID intentionally removed. Whatever dictionary is necessary is a hidden information.
1179 Note : this use case also happens when using a non-conformant dictionary.
1180 - `srcSize` is too small, and as a result, the frame header could not be decoded (only possible if `srcSize < ZSTD_FRAMEHEADERSIZE_MAX`).
1181 - This is not a Zstandard frame.
1182 When identifying the exact failure cause, it's possible to use ZSTD_getFrameHeader(), which will provide a more precise error code.
1185 <pre><b>size_t ZSTD_DCtx_loadDictionary_byReference(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
1186 </b><p> Same as ZSTD_DCtx_loadDictionary(),
1187 but references `dict` content instead of copying it into `dctx`.
1188 This saves memory if `dict` remains around.,
1189 However, it's imperative that `dict` remains accessible (and unmodified) while being used, so it must outlive decompression.
1192 <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);
1193 </b><p> Same as ZSTD_DCtx_loadDictionary(),
1194 but gives direct control over
1195 how to load the dictionary (by copy ? by reference ?)
1196 and how to interpret it (automatic ? force raw mode ? full mode only ?).
1199 <pre><b>size_t ZSTD_DCtx_refPrefix_advanced(ZSTD_DCtx* dctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType);
1200 </b><p> Same as ZSTD_DCtx_refPrefix(), but gives finer control over
1201 how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?)
1204 <pre><b>size_t ZSTD_DCtx_setMaxWindowSize(ZSTD_DCtx* dctx, size_t maxWindowSize);
1205 </b><p> Refuses allocating internal buffers for frames requiring a window size larger than provided limit.
1206 This protects a decoder context from reserving too much memory for itself (potential attack scenario).
1207 This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode.
1208 By default, a decompression context accepts all window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT)
1209 @return : 0, or an error code (which can be tested using ZSTD_isError()).
1213 <pre><b>size_t ZSTD_DCtx_setFormat(ZSTD_DCtx* dctx, ZSTD_format_e format);
1214 </b><p> Instruct the decoder context about what kind of data to decode next.
1215 This instruction is mandatory to decode data without a fully-formed header,
1216 such ZSTD_f_zstd1_magicless for example.
1217 @return : 0, or an error code (which can be tested using ZSTD_isError()).
1220 <pre><b>size_t ZSTD_decompressStream_simpleArgs (
1222 void* dst, size_t dstCapacity, size_t* dstPos,
1223 const void* src, size_t srcSize, size_t* srcPos);
1224 </b><p> Same as ZSTD_decompressStream(),
1225 but using only integral types as arguments.
1226 This can be helpful for binders from dynamic languages
1227 which have troubles handling structures containing memory pointers.
1231 <a name="Chapter19"></a><h2>Advanced streaming functions</h2><pre> Warning : most of these functions are now redundant with the Advanced API.
1232 Once Advanced API reaches "stable" status,
1233 redundant functions will be deprecated, and then at some point removed.
1236 <h3>Advanced Streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize); </b>/**< 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. */<b>
1237 size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); </b>/**< 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_dm_auto (treated as a full zstd dictionary if it begins with ZSTD_MAGIC_DICTIONARY, else as raw content) and ZSTD_dlm_byCopy.*/<b>
1238 size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize,
1239 ZSTD_parameters params, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize must be correct. If srcSize is not known at init time, use value ZSTD_CONTENTSIZE_UNKNOWN. dict is loaded with ZSTD_dm_auto and ZSTD_dlm_byCopy. */<b>
1240 size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict); </b>/**< note : cdict will just be referenced, and must outlive compression session */<b>
1241 size_t ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs, const ZSTD_CDict* cdict, ZSTD_frameParameters fParams, unsigned long long pledgedSrcSize); </b>/**< 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. */<b>
1243 <pre><b>size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize);
1244 </b><p> start a new frame, using same parameters from previous frame.
1245 This is typically useful to skip dictionary loading stage, since it will re-use it in-place.
1246 Note that zcs must be init at least once before using ZSTD_resetCStream().
1247 If pledgedSrcSize is not known at reset time, use macro ZSTD_CONTENTSIZE_UNKNOWN.
1248 If pledgedSrcSize > 0, its value must be correct, as it will be written in header, and controlled at the end.
1249 For the time being, pledgedSrcSize==0 is interpreted as "srcSize unknown" for compatibility with older programs,
1250 but it will change to mean "empty" in future version, so use macro ZSTD_CONTENTSIZE_UNKNOWN instead.
1251 @return : 0, or an error code (which can be tested using ZSTD_isError())
1255 <pre><b>typedef struct {
1256 unsigned long long ingested; </b>/* nb input bytes read and buffered */<b>
1257 unsigned long long consumed; </b>/* nb input bytes actually compressed */<b>
1258 unsigned long long produced; </b>/* nb of compressed bytes generated and buffered */<b>
1259 unsigned long long flushed; </b>/* nb of compressed bytes flushed : not provided; can be tracked from caller side */<b>
1260 unsigned currentJobID; </b>/* MT only : latest started job nb */<b>
1261 unsigned nbActiveWorkers; </b>/* MT only : nb of workers actively compressing at probe time */<b>
1262 } ZSTD_frameProgression;
1264 <pre><b>size_t ZSTD_toFlushNow(ZSTD_CCtx* cctx);
1265 </b><p> Tell how many bytes are ready to be flushed immediately.
1266 Useful for multithreading scenarios (nbWorkers >= 1).
1267 Probe the oldest active job, defined as oldest job not yet entirely flushed,
1268 and check its output buffer.
1269 @return : amount of data stored in oldest job and ready to be flushed immediately.
1270 if @return == 0, it means either :
1271 + there is no active job (could be checked with ZSTD_frameProgression()), or
1272 + oldest job is still actively compressing data,
1273 but everything it has produced has also been flushed so far,
1274 therefore flush speed is limited by production speed of oldest job
1275 irrespective of the speed of concurrent (and newer) jobs.
1279 <h3>Advanced Streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize); </b>/**< note: no dictionary will be used if dict == NULL or dictSize < 8 */<b>
1280 size_t ZSTD_initDStream_usingDDict(ZSTD_DStream* zds, const ZSTD_DDict* ddict); </b>/**< note : ddict is referenced, it must outlive decompression session */<b>
1281 size_t ZSTD_resetDStream(ZSTD_DStream* zds); </b>/**< re-use decompression parameters from previous init; saves dictionary loading */<b>
1283 <a name="Chapter20"></a><h2>Buffer-less and synchronous inner streaming functions</h2><pre>
1284 This is an advanced API, giving full control over buffer management, for users which need direct control over memory.
1285 But it's also a complex one, with several restrictions, documented below.
1286 Prefer normal streaming API for an easier experience.
1290 <a name="Chapter21"></a><h2>Buffer-less streaming compression (synchronous mode)</h2><pre>
1291 A ZSTD_CCtx object is required to track streaming operations.
1292 Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource.
1293 ZSTD_CCtx object can be re-used multiple times within successive compression operations.
1295 Start by initializing a context.
1296 Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression,
1297 or ZSTD_compressBegin_advanced(), for finer parameter control.
1298 It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx()
1300 Then, consume your input using ZSTD_compressContinue().
1301 There are some important considerations to keep in mind when using this advanced function :
1302 - ZSTD_compressContinue() has no internal buffer. It uses externally provided buffers only.
1303 - Interface is synchronous : input is consumed entirely and produces 1+ compressed blocks.
1304 - Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario.
1305 Worst case evaluation is provided by ZSTD_compressBound().
1306 ZSTD_compressContinue() doesn't guarantee recover after a failed compression.
1307 - ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog).
1308 It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks)
1309 - ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps.
1310 In which case, it will "discard" the relevant memory section from its history.
1312 Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum.
1313 It's possible to use srcSize==0, in which case, it will write a final empty block to end the frame.
1314 Without last block mark, frames are considered unfinished (hence corrupted) by compliant decoders.
1316 `ZSTD_CCtx` object can be re-used (ZSTD_compressBegin()) to compress again.
1319 <h3>Buffer-less streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel);
1320 size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel);
1321 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>
1322 size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); </b>/**< note: fails if cdict==NULL */<b>
1323 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>
1324 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>
1326 <a name="Chapter22"></a><h2>Buffer-less streaming decompression (synchronous mode)</h2><pre>
1327 A ZSTD_DCtx object is required to track streaming operations.
1328 Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it.
1329 A ZSTD_DCtx object can be re-used multiple times.
1331 First typical operation is to retrieve frame parameters, using ZSTD_getFrameHeader().
1332 Frame header is extracted from the beginning of compressed frame, so providing only the frame's beginning is enough.
1333 Data fragment must be large enough to ensure successful decoding.
1334 `ZSTD_frameHeaderSize_max` bytes is guaranteed to always be large enough.
1335 @result : 0 : successful decoding, the `ZSTD_frameHeader` structure is correctly filled.
1336 >0 : `srcSize` is too small, please provide at least @result bytes on next attempt.
1337 errorCode, which can be tested using ZSTD_isError().
1339 It fills a ZSTD_frameHeader structure with important information to correctly decode the frame,
1340 such as the dictionary ID, content size, or maximum back-reference distance (`windowSize`).
1341 Note that these values could be wrong, either because of data corruption, or because a 3rd party deliberately spoofs false information.
1342 As a consequence, check that values remain within valid application range.
1343 For example, do not allocate memory blindly, check that `windowSize` is within expectation.
1344 Each application can set its own limits, depending on local restrictions.
1345 For extended interoperability, it is recommended to support `windowSize` of at least 8 MB.
1347 ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize` bytes.
1348 ZSTD_decompressContinue() is very sensitive to contiguity,
1349 if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place,
1350 or that previous contiguous segment is large enough to properly handle maximum back-reference distance.
1351 There are multiple ways to guarantee this condition.
1353 The most memory efficient way is to use a round buffer of sufficient size.
1354 Sufficient size is determined by invoking ZSTD_decodingBufferSize_min(),
1355 which can @return an error code if required value is too large for current system (in 32-bits mode).
1356 In a round buffer methodology, ZSTD_decompressContinue() decompresses each block next to previous one,
1357 up to the moment there is not enough room left in the buffer to guarantee decoding another full block,
1358 which maximum size is provided in `ZSTD_frameHeader` structure, field `blockSizeMax`.
1359 At which point, decoding can resume from the beginning of the buffer.
1360 Note that already decoded data stored in the buffer should be flushed before being overwritten.
1362 There are alternatives possible, for example using two or more buffers of size `windowSize` each, though they consume more memory.
1364 Finally, if you control the compression process, you can also ignore all buffer size rules,
1365 as long as the encoder and decoder progress in "lock-step",
1366 aka use exactly the same buffer sizes, break contiguity at the same place, etc.
1368 Once buffers are setup, start decompression, with ZSTD_decompressBegin().
1369 If decompression requires a dictionary, use ZSTD_decompressBegin_usingDict() or ZSTD_decompressBegin_usingDDict().
1371 Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively.
1372 ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue().
1373 ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail.
1375 @result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity).
1376 It can be zero : it just means ZSTD_decompressContinue() has decoded some metadata item.
1377 It can also be an error code, which can be tested with ZSTD_isError().
1379 A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero.
1380 Context can then be reset to start a new decompression.
1382 Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType().
1383 This information is not required to properly decode a frame.
1385 == Special case : skippable frames
1387 Skippable frames allow integration of user-defined data into a flow of concatenated frames.
1388 Skippable frames will be ignored (skipped) by decompressor.
1389 The format of skippable frames is as follows :
1390 a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F
1391 b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits
1392 c) Frame Content - any content (User Data) of length equal to Frame Size
1393 For skippable frames ZSTD_getFrameHeader() returns zfhPtr->frameType==ZSTD_skippableFrame.
1394 For skippable frames ZSTD_decompressContinue() always returns 0 : it only skips the content.
1397 <h3>Buffer-less streaming decompression functions</h3><pre></pre><b><pre>typedef enum { ZSTD_frame, ZSTD_skippableFrame } ZSTD_frameType_e;
1399 unsigned long long frameContentSize; </b>/* if == ZSTD_CONTENTSIZE_UNKNOWN, it means this field is not available. 0 means "empty" */<b>
1400 unsigned long long windowSize; </b>/* can be very large, up to <= frameContentSize */<b>
1401 unsigned blockSizeMax;
1402 ZSTD_frameType_e frameType; </b>/* if == ZSTD_skippableFrame, frameContentSize is the size of skippable content */<b>
1403 unsigned headerSize;
1405 unsigned checksumFlag;
1408 <a name="Chapter23"></a><h2>ZSTD_getFrameHeader() :</h2><pre> decode Frame Header, or requires larger `srcSize`.
1409 @return : 0, `zfhPtr` is correctly filled,
1410 >0, `srcSize` is too small, value is wanted `srcSize` amount,
1411 or an error code, which can be tested using ZSTD_isError()
1414 <pre><b>size_t ZSTD_getFrameHeader(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize); </b>/**< doesn't consume input */<b>
1416 <pre><b>size_t ZSTD_getFrameHeader_advanced(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize, ZSTD_format_e format);
1417 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>
1418 </b><p> same as ZSTD_getFrameHeader(),
1419 with added capability to select a format (like ZSTD_f_zstd1_magicless)
1422 <pre><b>typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e;
1424 <a name="Chapter24"></a><h2>Block level API</h2><pre></pre>
1426 <pre><b></b><p> Frame metadata cost is typically ~18 bytes, which can be non-negligible for very small blocks (< 100 bytes).
1427 User will have to take in charge required information to regenerate data, such as compressed and content sizes.
1429 A few rules to respect :
1430 - Compressing and decompressing require a context structure
1431 + Use ZSTD_createCCtx() and ZSTD_createDCtx()
1432 - It is necessary to init context before starting
1433 + compression : any ZSTD_compressBegin*() variant, including with dictionary
1434 + decompression : any ZSTD_decompressBegin*() variant, including with dictionary
1435 + copyCCtx() and copyDCtx() can be used too
1436 - Block size is limited, it must be <= ZSTD_getBlockSize() <= ZSTD_BLOCKSIZE_MAX == 128 KB
1437 + If input is larger than a block size, it's necessary to split input data into multiple blocks
1438 + For inputs larger than a single block, really consider using regular ZSTD_compress() instead.
1439 Frame metadata is not that costly, and quickly becomes negligible as source size grows larger.
1440 - When a block is considered not compressible enough, ZSTD_compressBlock() result will be zero.
1441 In which case, nothing is produced into `dst` !
1442 + User must test for such outcome and deal directly with uncompressed data
1443 + ZSTD_decompressBlock() doesn't accept uncompressed data as input !!!
1444 + In case of multiple successive blocks, should some of them be uncompressed,
1445 decoder must be informed of their existence in order to follow proper history.
1446 Use ZSTD_insertBlock() for such a case.
1449 <h3>Raw zstd block functions</h3><pre></pre><b><pre>size_t ZSTD_getBlockSize (const ZSTD_CCtx* cctx);
1450 size_t ZSTD_compressBlock (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
1451 size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
1452 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>
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