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4 <title>zstd 1.2.0 Manual</title>
7 <h1>zstd 1.2.0 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">Simple API</a></li>
14 <li><a href="#Chapter4">Explicit memory management</a></li>
15 <li><a href="#Chapter5">Simple dictionary API</a></li>
16 <li><a href="#Chapter6">Fast dictionary API</a></li>
17 <li><a href="#Chapter7">Streaming</a></li>
18 <li><a href="#Chapter8">Streaming compression - HowTo</a></li>
19 <li><a href="#Chapter9">Streaming decompression - HowTo</a></li>
20 <li><a href="#Chapter10">START OF ADVANCED AND EXPERIMENTAL FUNCTIONS</a></li>
21 <li><a href="#Chapter11">Advanced types</a></li>
22 <li><a href="#Chapter12">Compressed size functions</a></li>
23 <li><a href="#Chapter13">Decompressed size functions</a></li>
24 <li><a href="#Chapter14">Advanced compression functions</a></li>
25 <li><a href="#Chapter15">Advanced decompression functions</a></li>
26 <li><a href="#Chapter16">Advanced streaming functions</a></li>
27 <li><a href="#Chapter17">Buffer-less and synchronous inner streaming functions</a></li>
28 <li><a href="#Chapter18">Buffer-less streaming compression (synchronous mode)</a></li>
29 <li><a href="#Chapter19">Buffer-less streaming decompression (synchronous mode)</a></li>
30 <li><a href="#Chapter20">Block functions</a></li>
33 <a name="Chapter1"></a><h2>Introduction</h2><pre>
34 zstd, short for Zstandard, is a fast lossless compression algorithm, targeting real-time compression scenarios
35 at zlib-level and better compression ratios. The zstd compression library provides in-memory compression and
36 decompression functions. The library supports compression levels from 1 up to ZSTD_maxCLevel() which is 22.
37 Levels >= 20, labeled `--ultra`, should be used with caution, as they require more memory.
38 Compression can be done in:
39 - a single step (described as Simple API)
40 - a single step, reusing a context (described as Explicit memory management)
41 - unbounded multiple steps (described as Streaming compression)
42 The compression ratio achievable on small data can be highly improved using compression with a dictionary in:
43 - a single step (described as Simple dictionary API)
44 - a single step, reusing a dictionary (described as Fast dictionary API)
46 Advanced experimental functions can be accessed using #define ZSTD_STATIC_LINKING_ONLY before including zstd.h.
47 These APIs shall never be used with a dynamic library.
48 They are not "stable", their definition may change in the future. Only static linking is allowed.
51 <a name="Chapter2"></a><h2>Version</h2><pre></pre>
53 <pre><b>unsigned ZSTD_versionNumber(void); </b>/**< library version number; to be used when checking dll version */<b>
55 <a name="Chapter3"></a><h2>Simple API</h2><pre></pre>
57 <pre><b>size_t ZSTD_compress( void* dst, size_t dstCapacity,
58 const void* src, size_t srcSize,
59 int compressionLevel);
60 </b><p> Compresses `src` content as a single zstd compressed frame into already allocated `dst`.
61 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`.
62 @return : compressed size written into `dst` (<= `dstCapacity),
63 or an error code if it fails (which can be tested using ZSTD_isError()).
66 <pre><b>size_t ZSTD_decompress( void* dst, size_t dstCapacity,
67 const void* src, size_t compressedSize);
68 </b><p> `compressedSize` : must be the _exact_ size of some number of compressed and/or skippable frames.
69 `dstCapacity` is an upper bound of originalSize.
70 If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data.
71 @return : the number of bytes decompressed into `dst` (<= `dstCapacity`),
72 or an errorCode if it fails (which can be tested using ZSTD_isError()).
75 <pre><b>unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize);
76 </b><p> NOTE: This function is planned to be obsolete, in favour of ZSTD_getFrameContentSize.
77 ZSTD_getFrameContentSize functions the same way, returning the decompressed size of a single
78 frame, but distinguishes empty frames from frames with an unknown size, or errors.
80 Additionally, ZSTD_findDecompressedSize can be used instead. It can handle multiple
81 concatenated frames in one buffer, and so is more general.
82 As a result however, it requires more computation and entire frames to be passed to it,
83 as opposed to ZSTD_getFrameContentSize which requires only a single frame's header.
85 'src' is the start of a zstd compressed frame.
86 @return : content size to be decompressed, as a 64-bits value _if known_, 0 otherwise.
87 note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
88 When `return==0`, data to decompress could be any size.
89 In which case, it's necessary to use streaming mode to decompress data.
90 Optionally, application can still use ZSTD_decompress() while relying on implied limits.
91 (For example, data may be necessarily cut into blocks <= 16 KB).
92 note 2 : decompressed size is always present when compression is done with ZSTD_compress()
93 note 3 : decompressed size can be very large (64-bits value),
94 potentially larger than what local system can handle as a single memory segment.
95 In which case, it's necessary to use streaming mode to decompress data.
96 note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified.
97 Always ensure result fits within application's authorized limits.
98 Each application can set its own limits.
99 note 5 : when `return==0`, if precise failure cause is needed, use ZSTD_getFrameParams() to know more.
102 <h3>Helper functions</h3><pre></pre><b><pre>int ZSTD_maxCLevel(void); </b>/*!< maximum compression level available */<b>
103 size_t ZSTD_compressBound(size_t srcSize); </b>/*!< maximum compressed size in worst case scenario */<b>
104 unsigned ZSTD_isError(size_t code); </b>/*!< tells if a `size_t` function result is an error code */<b>
105 const char* ZSTD_getErrorName(size_t code); </b>/*!< provides readable string from an error code */<b>
107 <a name="Chapter4"></a><h2>Explicit memory management</h2><pre></pre>
109 <h3>Compression context</h3><pre> When compressing many times,
110 it is recommended to allocate a context just once, and re-use it for each successive compression operation.
111 This will make workload friendlier for system's memory.
112 Use one context per thread for parallel execution in multi-threaded environments.
113 </pre><b><pre>typedef struct ZSTD_CCtx_s ZSTD_CCtx;
114 ZSTD_CCtx* ZSTD_createCCtx(void);
115 size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx);
117 <pre><b>size_t ZSTD_compressCCtx(ZSTD_CCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize, int compressionLevel);
118 </b><p> Same as ZSTD_compress(), requires an allocated ZSTD_CCtx (see ZSTD_createCCtx()).
121 <h3>Decompression context</h3><pre> When decompressing many times,
122 it is recommended to allocate a context just once, and re-use it for each successive compression operation.
123 This will make workload friendlier for system's memory.
124 Use one context per thread for parallel execution in multi-threaded environments.
125 </pre><b><pre>typedef struct ZSTD_DCtx_s ZSTD_DCtx;
126 ZSTD_DCtx* ZSTD_createDCtx(void);
127 size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx);
129 <pre><b>size_t ZSTD_decompressDCtx(ZSTD_DCtx* ctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
130 </b><p> Same as ZSTD_decompress(), requires an allocated ZSTD_DCtx (see ZSTD_createDCtx()).
133 <a name="Chapter5"></a><h2>Simple dictionary API</h2><pre></pre>
135 <pre><b>size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx,
136 void* dst, size_t dstCapacity,
137 const void* src, size_t srcSize,
138 const void* dict,size_t dictSize,
139 int compressionLevel);
140 </b><p> Compression using a predefined Dictionary (see dictBuilder/zdict.h).
141 Note : This function loads the dictionary, resulting in significant startup delay.
142 Note : When `dict == NULL || dictSize < 8` no dictionary is used.
145 <pre><b>size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx,
146 void* dst, size_t dstCapacity,
147 const void* src, size_t srcSize,
148 const void* dict,size_t dictSize);
149 </b><p> Decompression using a predefined Dictionary (see dictBuilder/zdict.h).
150 Dictionary must be identical to the one used during compression.
151 Note : This function loads the dictionary, resulting in significant startup delay.
152 Note : When `dict == NULL || dictSize < 8` no dictionary is used.
155 <a name="Chapter6"></a><h2>Fast dictionary API</h2><pre></pre>
157 <pre><b>ZSTD_CDict* ZSTD_createCDict(const void* dictBuffer, size_t dictSize, int compressionLevel);
158 </b><p> When compressing multiple messages / blocks with the same dictionary, it's recommended to load it just once.
159 ZSTD_createCDict() will create a digested dictionary, ready to start future compression operations without startup delay.
160 ZSTD_CDict can be created once and used by multiple threads concurrently, as its usage is read-only.
161 `dictBuffer` can be released after ZSTD_CDict creation, as its content is copied within CDict
164 <pre><b>size_t ZSTD_freeCDict(ZSTD_CDict* CDict);
165 </b><p> Function frees memory allocated by ZSTD_createCDict().
168 <pre><b>size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx,
169 void* dst, size_t dstCapacity,
170 const void* src, size_t srcSize,
171 const ZSTD_CDict* cdict);
172 </b><p> Compression using a digested Dictionary.
173 Faster startup than ZSTD_compress_usingDict(), recommended when same dictionary is used multiple times.
174 Note that compression level is decided during dictionary creation.
175 Frame parameters are hardcoded (dictID=yes, contentSize=yes, checksum=no)
178 <pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dictBuffer, size_t dictSize);
179 </b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
180 dictBuffer can be released after DDict creation, as its content is copied inside DDict
183 <pre><b>size_t ZSTD_freeDDict(ZSTD_DDict* ddict);
184 </b><p> Function frees memory allocated with ZSTD_createDDict()
187 <pre><b>size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx,
188 void* dst, size_t dstCapacity,
189 const void* src, size_t srcSize,
190 const ZSTD_DDict* ddict);
191 </b><p> Decompression using a digested Dictionary.
192 Faster startup than ZSTD_decompress_usingDict(), recommended when same dictionary is used multiple times.
195 <a name="Chapter7"></a><h2>Streaming</h2><pre></pre>
197 <pre><b>typedef struct ZSTD_inBuffer_s {
198 const void* src; </b>/**< start of input buffer */<b>
199 size_t size; </b>/**< size of input buffer */<b>
200 size_t pos; </b>/**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
203 <pre><b>typedef struct ZSTD_outBuffer_s {
204 void* dst; </b>/**< start of output buffer */<b>
205 size_t size; </b>/**< size of output buffer */<b>
206 size_t pos; </b>/**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */<b>
209 <a name="Chapter8"></a><h2>Streaming compression - HowTo</h2><pre>
210 A ZSTD_CStream object is required to track streaming operation.
211 Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources.
212 ZSTD_CStream objects can be reused multiple times on consecutive compression operations.
213 It is recommended to re-use ZSTD_CStream in situations where many streaming operations will be achieved consecutively,
214 since it will play nicer with system's memory, by re-using already allocated memory.
215 Use one separate ZSTD_CStream per thread for parallel execution.
217 Start a new compression by initializing ZSTD_CStream.
218 Use ZSTD_initCStream() to start a new compression operation.
219 Use ZSTD_initCStream_usingDict() or ZSTD_initCStream_usingCDict() for a compression which requires a dictionary (experimental section)
221 Use ZSTD_compressStream() repetitively to consume input stream.
222 The function will automatically update both `pos` fields.
223 Note that it may not consume the entire input, in which case `pos < size`,
224 and it's up to the caller to present again remaining data.
225 @return : a size hint, preferred nb of bytes to use as input for next function call
226 or an error code, which can be tested using ZSTD_isError().
227 Note 1 : it's just a hint, to help latency a little, any other value will work fine.
228 Note 2 : size hint is guaranteed to be <= ZSTD_CStreamInSize()
230 At any moment, it's possible to flush whatever data remains within internal buffer, using ZSTD_flushStream().
231 `output->pos` will be updated.
232 Note that some content might still be left within internal buffer if `output->size` is too small.
233 @return : nb of bytes still present within internal buffer (0 if it's empty)
234 or an error code, which can be tested using ZSTD_isError().
236 ZSTD_endStream() instructs to finish a frame.
237 It will perform a flush and write frame epilogue.
238 The epilogue is required for decoders to consider a frame completed.
239 Similar to ZSTD_flushStream(), it may not be able to flush the full content if `output->size` is too small.
240 In which case, call again ZSTD_endStream() to complete the flush.
241 @return : nb of bytes still present within internal buffer (0 if it's empty, hence compression completed)
242 or an error code, which can be tested using ZSTD_isError().
247 <h3>ZSTD_CStream management functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream(void);
248 size_t ZSTD_freeCStream(ZSTD_CStream* zcs);
250 <h3>Streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel);
251 size_t ZSTD_compressStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
252 size_t ZSTD_flushStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
253 size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output);
255 <pre><b>size_t ZSTD_CStreamInSize(void); </b>/**< recommended size for input buffer */<b>
257 <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>
259 <a name="Chapter9"></a><h2>Streaming decompression - HowTo</h2><pre>
260 A ZSTD_DStream object is required to track streaming operations.
261 Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources.
262 ZSTD_DStream objects can be re-used multiple times.
264 Use ZSTD_initDStream() to start a new decompression operation,
265 or ZSTD_initDStream_usingDict() if decompression requires a dictionary.
266 @return : recommended first input size
268 Use ZSTD_decompressStream() repetitively to consume your input.
269 The function will update both `pos` fields.
270 If `input.pos < input.size`, some input has not been consumed.
271 It's up to the caller to present again remaining data.
272 If `output.pos < output.size`, decoder has flushed everything it could.
273 @return : 0 when a frame is completely decoded and fully flushed,
274 an error code, which can be tested using ZSTD_isError(),
275 any other value > 0, which means there is still some decoding to do to complete current frame.
276 The return value is a suggested next input size (a hint to improve latency) that will never load more than the current frame.
280 <h3>ZSTD_DStream management functions</h3><pre></pre><b><pre>ZSTD_DStream* ZSTD_createDStream(void);
281 size_t ZSTD_freeDStream(ZSTD_DStream* zds);
283 <h3>Streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_initDStream(ZSTD_DStream* zds);
284 size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inBuffer* input);
286 <pre><b>size_t ZSTD_DStreamInSize(void); </b>/*!< recommended size for input buffer */<b>
288 <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>
290 <a name="Chapter10"></a><h2>START OF ADVANCED AND EXPERIMENTAL FUNCTIONS</h2><pre> The definitions in this section are considered experimental.
291 They should never be used with a dynamic library, as they may change in the future.
292 They are provided for advanced usages.
293 Use them only in association with static linking.
297 <a name="Chapter11"></a><h2>Advanced types</h2><pre></pre>
299 <pre><b>typedef enum { ZSTD_fast, ZSTD_dfast, ZSTD_greedy, ZSTD_lazy, ZSTD_lazy2, ZSTD_btlazy2, ZSTD_btopt, ZSTD_btopt2 } ZSTD_strategy; </b>/* from faster to stronger */<b>
301 <pre><b>typedef struct {
302 unsigned windowLog; </b>/**< largest match distance : larger == more compression, more memory needed during decompression */<b>
303 unsigned chainLog; </b>/**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */<b>
304 unsigned hashLog; </b>/**< dispatch table : larger == faster, more memory */<b>
305 unsigned searchLog; </b>/**< nb of searches : larger == more compression, slower */<b>
306 unsigned searchLength; </b>/**< match length searched : larger == faster decompression, sometimes less compression */<b>
307 unsigned targetLength; </b>/**< acceptable match size for optimal parser (only) : larger == more compression, slower */<b>
308 ZSTD_strategy strategy;
309 } ZSTD_compressionParameters;
311 <pre><b>typedef struct {
312 unsigned contentSizeFlag; </b>/**< 1: content size will be in frame header (when known) */<b>
313 unsigned checksumFlag; </b>/**< 1: generate a 32-bits checksum at end of frame, for error detection */<b>
314 unsigned noDictIDFlag; </b>/**< 1: no dictID will be saved into frame header (if dictionary compression) */<b>
315 } ZSTD_frameParameters;
317 <pre><b>typedef struct {
318 ZSTD_compressionParameters cParams;
319 ZSTD_frameParameters fParams;
322 <h3>Custom memory allocation functions</h3><pre></pre><b><pre>typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size);
323 typedef void (*ZSTD_freeFunction) (void* opaque, void* address);
324 typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem;
326 <a name="Chapter12"></a><h2>Compressed size functions</h2><pre></pre>
328 <pre><b>size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize);
329 </b><p> `src` should point to the start of a ZSTD encoded frame or skippable frame
330 `srcSize` must be at least as large as the frame
331 @return : the compressed size of the frame pointed to by `src`, suitable to pass to
332 `ZSTD_decompress` or similar, or an error code if given invalid input.
335 <a name="Chapter13"></a><h2>Decompressed size functions</h2><pre></pre>
337 <pre><b>unsigned long long ZSTD_getFrameContentSize(const void *src, size_t srcSize);
338 </b><p> `src` should point to the start of a ZSTD encoded frame
339 `srcSize` must be at least as large as the frame header. A value greater than or equal
340 to `ZSTD_frameHeaderSize_max` is guaranteed to be large enough in all cases.
341 @return : decompressed size of the frame pointed to be `src` if known, otherwise
342 - ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined
343 - ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small)
346 <pre><b>unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize);
347 </b><p> `src` should point the start of a series of ZSTD encoded and/or skippable frames
348 `srcSize` must be the _exact_ size of this series
349 (i.e. there should be a frame boundary exactly `srcSize` bytes after `src`)
350 @return : the decompressed size of all data in the contained frames, as a 64-bit value _if known_
351 - if the decompressed size cannot be determined: ZSTD_CONTENTSIZE_UNKNOWN
352 - if an error occurred: ZSTD_CONTENTSIZE_ERROR
354 note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode.
355 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size.
356 In which case, it's necessary to use streaming mode to decompress data.
357 Optionally, application can still use ZSTD_decompress() while relying on implied limits.
358 (For example, data may be necessarily cut into blocks <= 16 KB).
359 note 2 : decompressed size is always present when compression is done with ZSTD_compress()
360 note 3 : decompressed size can be very large (64-bits value),
361 potentially larger than what local system can handle as a single memory segment.
362 In which case, it's necessary to use streaming mode to decompress data.
363 note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified.
364 Always ensure result fits within application's authorized limits.
365 Each application can set its own limits.
366 note 5 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to
367 read each contained frame header. This is efficient as most of the data is skipped,
368 however it does mean that all frame data must be present and valid.
371 <a name="Chapter14"></a><h2>Advanced compression functions</h2><pre></pre>
373 <pre><b>size_t ZSTD_estimateCCtxSize(ZSTD_compressionParameters cParams);
374 </b><p> Gives the amount of memory allocated for a ZSTD_CCtx given a set of compression parameters.
375 `frameContentSize` is an optional parameter, provide `0` if unknown
378 <pre><b>ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem);
379 </b><p> Create a ZSTD compression context using external alloc and free functions
382 <pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx);
383 </b><p> Gives the amount of memory used by a given ZSTD_CCtx
386 <pre><b>typedef enum {
387 ZSTD_p_forceWindow, </b>/* Force back-references to remain < windowSize, even when referencing Dictionary content (default:0) */<b>
388 ZSTD_p_forceRawDict </b>/* Force loading dictionary in "content-only" mode (no header analysis) */<b>
389 } ZSTD_CCtxParameter;
391 <pre><b>size_t ZSTD_setCCtxParameter(ZSTD_CCtx* cctx, ZSTD_CCtxParameter param, unsigned value);
392 </b><p> Set advanced parameters, selected through enum ZSTD_CCtxParameter
393 @result : 0, or an error code (which can be tested with ZSTD_isError())
396 <pre><b>ZSTD_CDict* ZSTD_createCDict_byReference(const void* dictBuffer, size_t dictSize, int compressionLevel);
397 </b><p> Create a digested dictionary for compression
398 Dictionary content is simply referenced, and therefore stays in dictBuffer.
399 It is important that dictBuffer outlives CDict, it must remain read accessible throughout the lifetime of CDict
402 <pre><b>ZSTD_CDict* ZSTD_createCDict_advanced(const void* dict, size_t dictSize, unsigned byReference,
403 ZSTD_compressionParameters cParams, ZSTD_customMem customMem);
404 </b><p> Create a ZSTD_CDict using external alloc and free, and customized compression parameters
407 <pre><b>size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict);
408 </b><p> Gives the amount of memory used by a given ZSTD_sizeof_CDict
411 <pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
412 </b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize.
413 `estimatedSrcSize` value is optional, select 0 if not known
416 <pre><b>ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize);
417 </b><p> same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`.
418 All fields of `ZSTD_frameParameters` are set to default (0)
421 <pre><b>size_t ZSTD_checkCParams(ZSTD_compressionParameters params);
422 </b><p> Ensure param values remain within authorized range
425 <pre><b>ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize);
426 </b><p> optimize params for a given `srcSize` and `dictSize`.
427 both values are optional, select `0` if unknown.
430 <pre><b>size_t ZSTD_compress_advanced (ZSTD_CCtx* cctx,
431 void* dst, size_t dstCapacity,
432 const void* src, size_t srcSize,
433 const void* dict,size_t dictSize,
434 ZSTD_parameters params);
435 </b><p> Same as ZSTD_compress_usingDict(), with fine-tune control over each compression parameter
438 <pre><b>size_t ZSTD_compress_usingCDict_advanced(ZSTD_CCtx* cctx,
439 void* dst, size_t dstCapacity,
440 const void* src, size_t srcSize,
441 const ZSTD_CDict* cdict, ZSTD_frameParameters fParams);
442 </b><p> Same as ZSTD_compress_usingCDict(), with fine-tune control over frame parameters
445 <a name="Chapter15"></a><h2>Advanced decompression functions</h2><pre></pre>
447 <pre><b>unsigned ZSTD_isFrame(const void* buffer, size_t size);
448 </b><p> Tells if the content of `buffer` starts with a valid Frame Identifier.
449 Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0.
450 Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled.
451 Note 3 : Skippable Frame Identifiers are considered valid.
454 <pre><b>size_t ZSTD_estimateDCtxSize(void);
455 </b><p> Gives the potential amount of memory allocated to create a ZSTD_DCtx
458 <pre><b>ZSTD_DCtx* ZSTD_createDCtx_advanced(ZSTD_customMem customMem);
459 </b><p> Create a ZSTD decompression context using external alloc and free functions
462 <pre><b>size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx);
463 </b><p> Gives the amount of memory used by a given ZSTD_DCtx
466 <pre><b>ZSTD_DDict* ZSTD_createDDict_byReference(const void* dictBuffer, size_t dictSize);
467 </b><p> Create a digested dictionary, ready to start decompression operation without startup delay.
468 Dictionary content is simply referenced, and therefore stays in dictBuffer.
469 It is important that dictBuffer outlives DDict, it must remain read accessible throughout the lifetime of DDict
472 <pre><b>ZSTD_DDict* ZSTD_createDDict_advanced(const void* dict, size_t dictSize,
473 unsigned byReference, ZSTD_customMem customMem);
474 </b><p> Create a ZSTD_DDict using external alloc and free, optionally by reference
477 <pre><b>size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict);
478 </b><p> Gives the amount of memory used by a given ZSTD_DDict
481 <pre><b>unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize);
482 </b><p> Provides the dictID stored within dictionary.
483 if @return == 0, the dictionary is not conformant with Zstandard specification.
484 It can still be loaded, but as a content-only dictionary.
487 <pre><b>unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict);
488 </b><p> Provides the dictID of the dictionary loaded into `ddict`.
489 If @return == 0, the dictionary is not conformant to Zstandard specification, or empty.
490 Non-conformant dictionaries can still be loaded, but as content-only dictionaries.
493 <pre><b>unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize);
494 </b><p> Provides the dictID required to decompressed the frame stored within `src`.
495 If @return == 0, the dictID could not be decoded.
496 This could for one of the following reasons :
497 - The frame does not require a dictionary to be decoded (most common case).
498 - The frame was built with dictID intentionally removed. Whatever dictionary is necessary is a hidden information.
499 Note : this use case also happens when using a non-conformant dictionary.
500 - `srcSize` is too small, and as a result, the frame header could not be decoded (only possible if `srcSize < ZSTD_FRAMEHEADERSIZE_MAX`).
501 - This is not a Zstandard frame.
502 When identifying the exact failure cause, it's possible to use ZSTD_getFrameParams(), which will provide a more precise error code.
505 <a name="Chapter16"></a><h2>Advanced streaming functions</h2><pre></pre>
507 <h3>Advanced Streaming compression functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream_advanced(ZSTD_customMem customMem);
508 size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs); </b>/**< size of CStream is variable, depending primarily on compression level */<b>
509 size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize must be correct, a size of 0 means unknown. for a frame size of 0 use initCStream_advanced */<b>
510 size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); </b>/**< note: a dict will not be used if dict == NULL or dictSize < 8 */<b>
511 size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize,
512 ZSTD_parameters params, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize is optional and can be 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0 */<b>
513 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>
514 size_t ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs, const ZSTD_CDict* cdict, unsigned long long pledgedSrcSize, ZSTD_frameParameters fParams); </b>/**< same as ZSTD_initCStream_usingCDict(), with control over frame parameters */<b>
516 <pre><b>size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize);
517 </b><p> start a new compression job, using same parameters from previous job.
518 This is typically useful to skip dictionary loading stage, since it will re-use it in-place..
519 Note that zcs must be init at least once before using ZSTD_resetCStream().
520 pledgedSrcSize==0 means "srcSize unknown".
521 If pledgedSrcSize > 0, its value must be correct, as it will be written in header, and controlled at the end.
522 @return : 0, or an error code (which can be tested using ZSTD_isError())
525 <h3>Advanced Streaming decompression functions</h3><pre></pre><b><pre>typedef enum { DStream_p_maxWindowSize } ZSTD_DStreamParameter_e;
526 ZSTD_DStream* ZSTD_createDStream_advanced(ZSTD_customMem customMem);
527 size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize); </b>/**< note: a dict will not be used if dict == NULL or dictSize < 8 */<b>
528 size_t ZSTD_setDStreamParameter(ZSTD_DStream* zds, ZSTD_DStreamParameter_e paramType, unsigned paramValue);
529 size_t ZSTD_initDStream_usingDDict(ZSTD_DStream* zds, const ZSTD_DDict* ddict); </b>/**< note : ddict will just be referenced, and must outlive decompression session */<b>
530 size_t ZSTD_resetDStream(ZSTD_DStream* zds); </b>/**< re-use decompression parameters from previous init; saves dictionary loading */<b>
531 size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds);
533 <a name="Chapter17"></a><h2>Buffer-less and synchronous inner streaming functions</h2><pre>
534 This is an advanced API, giving full control over buffer management, for users which need direct control over memory.
535 But it's also a complex one, with many restrictions (documented below).
536 Prefer using normal streaming API for an easier experience
540 <a name="Chapter18"></a><h2>Buffer-less streaming compression (synchronous mode)</h2><pre>
541 A ZSTD_CCtx object is required to track streaming operations.
542 Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource.
543 ZSTD_CCtx object can be re-used multiple times within successive compression operations.
545 Start by initializing a context.
546 Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression,
547 or ZSTD_compressBegin_advanced(), for finer parameter control.
548 It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx()
550 Then, consume your input using ZSTD_compressContinue().
551 There are some important considerations to keep in mind when using this advanced function :
552 - ZSTD_compressContinue() has no internal buffer. It uses externally provided buffer only.
553 - Interface is synchronous : input is consumed entirely and produce 1+ (or more) compressed blocks.
554 - Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario.
555 Worst case evaluation is provided by ZSTD_compressBound().
556 ZSTD_compressContinue() doesn't guarantee recover after a failed compression.
557 - ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog).
558 It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks)
559 - ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps.
560 In which case, it will "discard" the relevant memory section from its history.
562 Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum.
563 It's possible to use srcSize==0, in which case, it will write a final empty block to end the frame.
564 Without last block mark, frames will be considered unfinished (corrupted) by decoders.
566 `ZSTD_CCtx` object can be re-used (ZSTD_compressBegin()) to compress some new frame.
569 <h3>Buffer-less streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel);
570 size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel);
571 size_t ZSTD_compressBegin_advanced(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, ZSTD_parameters params, unsigned long long pledgedSrcSize); </b>/**< pledgedSrcSize is optional and can be 0 (meaning unknown). note: if the contentSizeFlag is set, pledgedSrcSize == 0 means the source size is actually 0 */<b>
572 size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); </b>/**< note: fails if cdict==NULL */<b>
573 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=0 means null-size */<b>
574 size_t ZSTD_copyCCtx(ZSTD_CCtx* cctx, const ZSTD_CCtx* preparedCCtx, unsigned long long pledgedSrcSize); </b>/**< note: if pledgedSrcSize can be 0, indicating unknown size. if it is non-zero, it must be accurate. for 0 size frames, use compressBegin_advanced */<b>
576 <a name="Chapter19"></a><h2>Buffer-less streaming decompression (synchronous mode)</h2><pre>
577 A ZSTD_DCtx object is required to track streaming operations.
578 Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it.
579 A ZSTD_DCtx object can be re-used multiple times.
581 First typical operation is to retrieve frame parameters, using ZSTD_getFrameParams().
582 It fills a ZSTD_frameParams structure which provide important information to correctly decode the frame,
583 such as the minimum rolling buffer size to allocate to decompress data (`windowSize`),
584 and the dictionary ID used.
585 (Note : content size is optional, it may not be present. 0 means : content size unknown).
586 Note that these values could be wrong, either because of data malformation, or because an attacker is spoofing deliberate false information.
587 As a consequence, check that values remain within valid application range, especially `windowSize`, before allocation.
588 Each application can set its own limit, depending on local restrictions. For extended interoperability, it is recommended to support at least 8 MB.
589 Frame parameters are extracted from the beginning of the compressed frame.
590 Data fragment must be large enough to ensure successful decoding, typically `ZSTD_frameHeaderSize_max` bytes.
591 @result : 0 : successful decoding, the `ZSTD_frameParams` structure is correctly filled.
592 >0 : `srcSize` is too small, please provide at least @result bytes on next attempt.
593 errorCode, which can be tested using ZSTD_isError().
595 Start decompression, with ZSTD_decompressBegin() or ZSTD_decompressBegin_usingDict().
596 Alternatively, you can copy a prepared context, using ZSTD_copyDCtx().
598 Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively.
599 ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue().
600 ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail.
602 @result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity).
603 It can be zero, which is not an error; it just means ZSTD_decompressContinue() has decoded some metadata item.
604 It can also be an error code, which can be tested with ZSTD_isError().
606 ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize`.
607 They should preferably be located contiguously, prior to current block.
608 Alternatively, a round buffer of sufficient size is also possible. Sufficient size is determined by frame parameters.
609 ZSTD_decompressContinue() is very sensitive to contiguity,
610 if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place,
611 or that previous contiguous segment is large enough to properly handle maximum back-reference.
613 A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero.
614 Context can then be reset to start a new decompression.
616 Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType().
617 This information is not required to properly decode a frame.
619 == Special case : skippable frames
621 Skippable frames allow integration of user-defined data into a flow of concatenated frames.
622 Skippable frames will be ignored (skipped) by a decompressor. The format of skippable frames is as follows :
623 a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F
624 b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits
625 c) Frame Content - any content (User Data) of length equal to Frame Size
626 For skippable frames ZSTD_decompressContinue() always returns 0.
627 For skippable frames ZSTD_getFrameParams() returns fparamsPtr->windowLog==0 what means that a frame is skippable.
628 Note : If fparamsPtr->frameContentSize==0, it is ambiguous: the frame might actually be a Zstd encoded frame with no content.
629 For purposes of decompression, it is valid in both cases to skip the frame using
630 ZSTD_findFrameCompressedSize to find its size in bytes.
631 It also returns Frame Size as fparamsPtr->frameContentSize.
634 <pre><b>typedef struct {
635 unsigned long long frameContentSize;
638 unsigned checksumFlag;
641 <h3>Buffer-less streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_getFrameParams(ZSTD_frameParams* fparamsPtr, const void* src, size_t srcSize); </b>/**< doesn't consume input, see details below */<b>
642 size_t ZSTD_decompressBegin(ZSTD_DCtx* dctx);
643 size_t ZSTD_decompressBegin_usingDict(ZSTD_DCtx* dctx, const void* dict, size_t dictSize);
644 void ZSTD_copyDCtx(ZSTD_DCtx* dctx, const ZSTD_DCtx* preparedDCtx);
645 size_t ZSTD_nextSrcSizeToDecompress(ZSTD_DCtx* dctx);
646 size_t ZSTD_decompressContinue(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
647 typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e;
648 ZSTD_nextInputType_e ZSTD_nextInputType(ZSTD_DCtx* dctx);
650 <a name="Chapter20"></a><h2>Block functions</h2><pre>
651 Block functions produce and decode raw zstd blocks, without frame metadata.
652 Frame metadata cost is typically ~18 bytes, which can be non-negligible for very small blocks (< 100 bytes).
653 User will have to take in charge required information to regenerate data, such as compressed and content sizes.
655 A few rules to respect :
656 - Compressing and decompressing require a context structure
657 + Use ZSTD_createCCtx() and ZSTD_createDCtx()
658 - It is necessary to init context before starting
659 + compression : any ZSTD_compressBegin*() variant, including with dictionary
660 + decompression : any ZSTD_decompressBegin*() variant, including with dictionary
661 + copyCCtx() and copyDCtx() can be used too
662 - Block size is limited, it must be <= ZSTD_getBlockSizeMax() <= ZSTD_BLOCKSIZE_ABSOLUTEMAX
663 + If input is larger than a block size, it's necessary to split input data into multiple blocks
664 + For inputs larger than a single block size, consider using the regular ZSTD_compress() instead.
665 Frame metadata is not that costly, and quickly becomes negligible as source size grows larger.
666 - When a block is considered not compressible enough, ZSTD_compressBlock() result will be zero.
667 In which case, nothing is produced into `dst`.
668 + User must test for such outcome and deal directly with uncompressed data
669 + ZSTD_decompressBlock() doesn't accept uncompressed data as input !!!
670 + In case of multiple successive blocks, should some of them be uncompressed,
671 decoder must be informed of their existence in order to follow proper history.
672 Use ZSTD_insertBlock() for such a case.
675 <h3>Raw zstd block functions</h3><pre></pre><b><pre>size_t ZSTD_getBlockSizeMax(ZSTD_CCtx* cctx);
676 size_t ZSTD_compressBlock (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
677 size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize);
678 size_t ZSTD_insertBlock(ZSTD_DCtx* dctx, const void* blockStart, size_t blockSize); </b>/**< insert block into `dctx` history. Useful for uncompressed blocks */<b>
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