1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 4<title>zstd 1.4.2 Manual</title> 5</head> 6<body> 7<h1>zstd 1.4.2 Manual</h1> 8<hr> 9<a name="Contents"></a><h2>Contents</h2> 10<ol> 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 context</a></li> 15<li><a href="#Chapter5">Advanced compression API</a></li> 16<li><a href="#Chapter6">Advanced decompression 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">Simple dictionary API</a></li> 21<li><a href="#Chapter11">Bulk processing dictionary API</a></li> 22<li><a href="#Chapter12">Dictionary helper functions</a></li> 23<li><a href="#Chapter13">Advanced dictionary and prefix 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">Block level API</a></li> 34</ol> 35<hr> 36<a name="Chapter1"></a><h2>Introduction</h2><pre> 37 zstd, short for Zstandard, is a fast lossless compression algorithm, targeting 38 real-time compression scenarios at zlib-level and better compression ratios. 39 The zstd compression library provides in-memory compression and decompression 40 functions. 41 42 The library supports regular compression levels from 1 up to ZSTD_maxCLevel(), 43 which is currently 22. Levels >= 20, labeled `--ultra`, should be used with 44 caution, as they require more memory. The library also offers negative 45 compression levels, which extend the range of speed vs. ratio preferences. 46 The lower the level, the faster the speed (at the cost of compression). 47 48 Compression can be done in: 49 - a single step (described as Simple API) 50 - a single step, reusing a context (described as Explicit context) 51 - unbounded multiple steps (described as Streaming compression) 52 53 The compression ratio achievable on small data can be highly improved using 54 a dictionary. Dictionary compression can be performed in: 55 - a single step (described as Simple dictionary API) 56 - a single step, reusing a dictionary (described as Bulk-processing 57 dictionary API) 58 59 Advanced experimental functions can be accessed using 60 `#define ZSTD_STATIC_LINKING_ONLY` before including zstd.h. 61 62 Advanced experimental APIs should never be used with a dynamically-linked 63 library. They are not "stable"; their definitions or signatures may change in 64 the future. Only static linking is allowed. 65<BR></pre> 66 67<a name="Chapter2"></a><h2>Version</h2><pre></pre> 68 69<pre><b>unsigned ZSTD_versionNumber(void); </b>/**< to check runtime library version */<b> 70</b></pre><BR> 71<a name="Chapter3"></a><h2>Simple API</h2><pre></pre> 72 73<pre><b>size_t ZSTD_compress( void* dst, size_t dstCapacity, 74 const void* src, size_t srcSize, 75 int compressionLevel); 76</b><p> Compresses `src` content as a single zstd compressed frame into already allocated `dst`. 77 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`. 78 @return : compressed size written into `dst` (<= `dstCapacity), 79 or an error code if it fails (which can be tested using ZSTD_isError()). 80</p></pre><BR> 81 82<pre><b>size_t ZSTD_decompress( void* dst, size_t dstCapacity, 83 const void* src, size_t compressedSize); 84</b><p> `compressedSize` : must be the _exact_ size of some number of compressed and/or skippable frames. 85 `dstCapacity` is an upper bound of originalSize to regenerate. 86 If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data. 87 @return : the number of bytes decompressed into `dst` (<= `dstCapacity`), 88 or an errorCode if it fails (which can be tested using ZSTD_isError()). 89</p></pre><BR> 90 91<pre><b>#define ZSTD_CONTENTSIZE_UNKNOWN (0ULL - 1) 92#define ZSTD_CONTENTSIZE_ERROR (0ULL - 2) 93unsigned long long ZSTD_getFrameContentSize(const void *src, size_t srcSize); 94</b><p> `src` should point to the start of a ZSTD encoded frame. 95 `srcSize` must be at least as large as the frame header. 96 hint : any size >= `ZSTD_frameHeaderSize_max` is large enough. 97 @return : - decompressed size of `src` frame content, if known 98 - ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined 99 - ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small) 100 note 1 : a 0 return value means the frame is valid but "empty". 101 note 2 : decompressed size is an optional field, it may not be present, typically in streaming mode. 102 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size. 103 In which case, it's necessary to use streaming mode to decompress data. 104 Optionally, application can rely on some implicit limit, 105 as ZSTD_decompress() only needs an upper bound of decompressed size. 106 (For example, data could be necessarily cut into blocks <= 16 KB). 107 note 3 : decompressed size is always present when compression is completed using single-pass functions, 108 such as ZSTD_compress(), ZSTD_compressCCtx() ZSTD_compress_usingDict() or ZSTD_compress_usingCDict(). 109 note 4 : decompressed size can be very large (64-bits value), 110 potentially larger than what local system can handle as a single memory segment. 111 In which case, it's necessary to use streaming mode to decompress data. 112 note 5 : If source is untrusted, decompressed size could be wrong or intentionally modified. 113 Always ensure return value fits within application's authorized limits. 114 Each application can set its own limits. 115 note 6 : This function replaces ZSTD_getDecompressedSize() 116</p></pre><BR> 117 118<pre><b>unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize); 119</b><p> NOTE: This function is now obsolete, in favor of ZSTD_getFrameContentSize(). 120 Both functions work the same way, but ZSTD_getDecompressedSize() blends 121 "empty", "unknown" and "error" results to the same return value (0), 122 while ZSTD_getFrameContentSize() gives them separate return values. 123 @return : decompressed size of `src` frame content _if known and not empty_, 0 otherwise. 124</p></pre><BR> 125 126<pre><b>size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize); 127</b><p> `src` should point to the start of a ZSTD frame or skippable frame. 128 `srcSize` must be >= first frame size 129 @return : the compressed size of the first frame starting at `src`, 130 suitable to pass as `srcSize` to `ZSTD_decompress` or similar, 131 or an error code if input is invalid 132</p></pre><BR> 133 134<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> 135size_t ZSTD_compressBound(size_t srcSize); </b>/*!< maximum compressed size in worst case single-pass scenario */<b> 136unsigned ZSTD_isError(size_t code); </b>/*!< tells if a `size_t` function result is an error code */<b> 137const char* ZSTD_getErrorName(size_t code); </b>/*!< provides readable string from an error code */<b> 138int ZSTD_minCLevel(void); </b>/*!< minimum negative compression level allowed */<b> 139int ZSTD_maxCLevel(void); </b>/*!< maximum compression level available */<b> 140</pre></b><BR> 141<a name="Chapter4"></a><h2>Explicit context</h2><pre></pre> 142 143<h3>Compression context</h3><pre> When compressing many times, 144 it is recommended to allocate a context just once, 145 and re-use it for each successive compression operation. 146 This will make workload friendlier for system's memory. 147 Note : re-using context is just a speed / resource optimization. 148 It doesn't change the compression ratio, which remains identical. 149 Note 2 : In multi-threaded environments, 150 use one different context per thread for parallel execution. 151 152</pre><b><pre>typedef struct ZSTD_CCtx_s ZSTD_CCtx; 153ZSTD_CCtx* ZSTD_createCCtx(void); 154size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx); 155</pre></b><BR> 156<pre><b>size_t ZSTD_compressCCtx(ZSTD_CCtx* cctx, 157 void* dst, size_t dstCapacity, 158 const void* src, size_t srcSize, 159 int compressionLevel); 160</b><p> Same as ZSTD_compress(), using an explicit ZSTD_CCtx 161 The function will compress at requested compression level, 162 ignoring any other parameter 163</p></pre><BR> 164 165<h3>Decompression context</h3><pre> When decompressing many times, 166 it is recommended to allocate a context only once, 167 and re-use it for each successive compression operation. 168 This will make workload friendlier for system's memory. 169 Use one context per thread for parallel execution. 170</pre><b><pre>typedef struct ZSTD_DCtx_s ZSTD_DCtx; 171ZSTD_DCtx* ZSTD_createDCtx(void); 172size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx); 173</pre></b><BR> 174<pre><b>size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx, 175 void* dst, size_t dstCapacity, 176 const void* src, size_t srcSize); 177</b><p> Same as ZSTD_decompress(), 178 requires an allocated ZSTD_DCtx. 179 Compatible with sticky parameters. 180 181</p></pre><BR> 182 183<a name="Chapter5"></a><h2>Advanced compression API</h2><pre></pre> 184 185<pre><b>typedef enum { ZSTD_fast=1, 186 ZSTD_dfast=2, 187 ZSTD_greedy=3, 188 ZSTD_lazy=4, 189 ZSTD_lazy2=5, 190 ZSTD_btlazy2=6, 191 ZSTD_btopt=7, 192 ZSTD_btultra=8, 193 ZSTD_btultra2=9 194 </b>/* note : new strategies _might_ be added in the future.<b> 195 Only the order (from fast to strong) is guaranteed */ 196} ZSTD_strategy; 197</b></pre><BR> 198<pre><b>typedef enum { 199 200 </b>/* compression parameters<b> 201 * Note: When compressing with a ZSTD_CDict these parameters are superseded 202 * by the parameters used to construct the ZSTD_CDict. See ZSTD_CCtx_refCDict() 203 * for more info (superseded-by-cdict). */ 204 ZSTD_c_compressionLevel=100, </b>/* Update all compression parameters according to pre-defined cLevel table<b> 205 * Default level is ZSTD_CLEVEL_DEFAULT==3. 206 * Special: value 0 means default, which is controlled by ZSTD_CLEVEL_DEFAULT. 207 * Note 1 : it's possible to pass a negative compression level. 208 * Note 2 : setting a level sets all default values of other compression parameters */ 209 ZSTD_c_windowLog=101, </b>/* Maximum allowed back-reference distance, expressed as power of 2.<b> 210 * Must be clamped between ZSTD_WINDOWLOG_MIN and ZSTD_WINDOWLOG_MAX. 211 * Special: value 0 means "use default windowLog". 212 * Note: Using a windowLog greater than ZSTD_WINDOWLOG_LIMIT_DEFAULT 213 * requires explicitly allowing such window size at decompression stage if using streaming. */ 214 ZSTD_c_hashLog=102, </b>/* Size of the initial probe table, as a power of 2.<b> 215 * Resulting memory usage is (1 << (hashLog+2)). 216 * Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX. 217 * Larger tables improve compression ratio of strategies <= dFast, 218 * and improve speed of strategies > dFast. 219 * Special: value 0 means "use default hashLog". */ 220 ZSTD_c_chainLog=103, </b>/* Size of the multi-probe search table, as a power of 2.<b> 221 * Resulting memory usage is (1 << (chainLog+2)). 222 * Must be clamped between ZSTD_CHAINLOG_MIN and ZSTD_CHAINLOG_MAX. 223 * Larger tables result in better and slower compression. 224 * This parameter is useless when using "fast" strategy. 225 * It's still useful when using "dfast" strategy, 226 * in which case it defines a secondary probe table. 227 * Special: value 0 means "use default chainLog". */ 228 ZSTD_c_searchLog=104, </b>/* Number of search attempts, as a power of 2.<b> 229 * More attempts result in better and slower compression. 230 * This parameter is useless when using "fast" and "dFast" strategies. 231 * Special: value 0 means "use default searchLog". */ 232 ZSTD_c_minMatch=105, </b>/* Minimum size of searched matches.<b> 233 * Note that Zstandard can still find matches of smaller size, 234 * it just tweaks its search algorithm to look for this size and larger. 235 * Larger values increase compression and decompression speed, but decrease ratio. 236 * Must be clamped between ZSTD_MINMATCH_MIN and ZSTD_MINMATCH_MAX. 237 * Note that currently, for all strategies < btopt, effective minimum is 4. 238 * , for all strategies > fast, effective maximum is 6. 239 * Special: value 0 means "use default minMatchLength". */ 240 ZSTD_c_targetLength=106, </b>/* Impact of this field depends on strategy.<b> 241 * For strategies btopt, btultra & btultra2: 242 * Length of Match considered "good enough" to stop search. 243 * Larger values make compression stronger, and slower. 244 * For strategy fast: 245 * Distance between match sampling. 246 * Larger values make compression faster, and weaker. 247 * Special: value 0 means "use default targetLength". */ 248 ZSTD_c_strategy=107, </b>/* See ZSTD_strategy enum definition.<b> 249 * The higher the value of selected strategy, the more complex it is, 250 * resulting in stronger and slower compression. 251 * Special: value 0 means "use default strategy". */ 252 253 </b>/* LDM mode parameters */<b> 254 ZSTD_c_enableLongDistanceMatching=160, </b>/* Enable long distance matching.<b> 255 * This parameter is designed to improve compression ratio 256 * for large inputs, by finding large matches at long distance. 257 * It increases memory usage and window size. 258 * Note: enabling this parameter increases default ZSTD_c_windowLog to 128 MB 259 * except when expressly set to a different value. */ 260 ZSTD_c_ldmHashLog=161, </b>/* Size of the table for long distance matching, as a power of 2.<b> 261 * Larger values increase memory usage and compression ratio, 262 * but decrease compression speed. 263 * Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX 264 * default: windowlog - 7. 265 * Special: value 0 means "automatically determine hashlog". */ 266 ZSTD_c_ldmMinMatch=162, </b>/* Minimum match size for long distance matcher.<b> 267 * Larger/too small values usually decrease compression ratio. 268 * Must be clamped between ZSTD_LDM_MINMATCH_MIN and ZSTD_LDM_MINMATCH_MAX. 269 * Special: value 0 means "use default value" (default: 64). */ 270 ZSTD_c_ldmBucketSizeLog=163, </b>/* Log size of each bucket in the LDM hash table for collision resolution.<b> 271 * Larger values improve collision resolution but decrease compression speed. 272 * The maximum value is ZSTD_LDM_BUCKETSIZELOG_MAX. 273 * Special: value 0 means "use default value" (default: 3). */ 274 ZSTD_c_ldmHashRateLog=164, </b>/* Frequency of inserting/looking up entries into the LDM hash table.<b> 275 * Must be clamped between 0 and (ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN). 276 * Default is MAX(0, (windowLog - ldmHashLog)), optimizing hash table usage. 277 * Larger values improve compression speed. 278 * Deviating far from default value will likely result in a compression ratio decrease. 279 * Special: value 0 means "automatically determine hashRateLog". */ 280 281 </b>/* frame parameters */<b> 282 ZSTD_c_contentSizeFlag=200, </b>/* Content size will be written into frame header _whenever known_ (default:1)<b> 283 * Content size must be known at the beginning of compression. 284 * This is automatically the case when using ZSTD_compress2(), 285 * For streaming variants, content size must be provided with ZSTD_CCtx_setPledgedSrcSize() */ 286 ZSTD_c_checksumFlag=201, </b>/* A 32-bits checksum of content is written at end of frame (default:0) */<b> 287 ZSTD_c_dictIDFlag=202, </b>/* When applicable, dictionary's ID is written into frame header (default:1) */<b> 288 289 </b>/* multi-threading parameters */<b> 290 </b>/* These parameters are only useful if multi-threading is enabled (compiled with build macro ZSTD_MULTITHREAD).<b> 291 * They return an error otherwise. */ 292 ZSTD_c_nbWorkers=400, </b>/* Select how many threads will be spawned to compress in parallel.<b> 293 * When nbWorkers >= 1, triggers asynchronous mode when used with ZSTD_compressStream*() : 294 * ZSTD_compressStream*() consumes input and flush output if possible, but immediately gives back control to caller, 295 * while compression work is performed in parallel, within worker threads. 296 * (note : a strong exception to this rule is when first invocation of ZSTD_compressStream2() sets ZSTD_e_end : 297 * in which case, ZSTD_compressStream2() delegates to ZSTD_compress2(), which is always a blocking call). 298 * More workers improve speed, but also increase memory usage. 299 * Default value is `0`, aka "single-threaded mode" : no worker is spawned, compression is performed inside Caller's thread, all invocations are blocking */ 300 ZSTD_c_jobSize=401, </b>/* Size of a compression job. This value is enforced only when nbWorkers >= 1.<b> 301 * Each compression job is completed in parallel, so this value can indirectly impact the nb of active threads. 302 * 0 means default, which is dynamically determined based on compression parameters. 303 * Job size must be a minimum of overlap size, or 1 MB, whichever is largest. 304 * The minimum size is automatically and transparently enforced */ 305 ZSTD_c_overlapLog=402, </b>/* Control the overlap size, as a fraction of window size.<b> 306 * The overlap size is an amount of data reloaded from previous job at the beginning of a new job. 307 * It helps preserve compression ratio, while each job is compressed in parallel. 308 * This value is enforced only when nbWorkers >= 1. 309 * Larger values increase compression ratio, but decrease speed. 310 * Possible values range from 0 to 9 : 311 * - 0 means "default" : value will be determined by the library, depending on strategy 312 * - 1 means "no overlap" 313 * - 9 means "full overlap", using a full window size. 314 * Each intermediate rank increases/decreases load size by a factor 2 : 315 * 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 316 * default value varies between 6 and 9, depending on strategy */ 317 318 </b>/* note : additional experimental parameters are also available<b> 319 * within the experimental section of the API. 320 * At the time of this writing, they include : 321 * ZSTD_c_rsyncable 322 * ZSTD_c_format 323 * ZSTD_c_forceMaxWindow 324 * ZSTD_c_forceAttachDict 325 * ZSTD_c_literalCompressionMode 326 * ZSTD_c_targetCBlockSize 327 * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them. 328 * note : never ever use experimentalParam? names directly; 329 * also, the enums values themselves are unstable and can still change. 330 */ 331 ZSTD_c_experimentalParam1=500, 332 ZSTD_c_experimentalParam2=10, 333 ZSTD_c_experimentalParam3=1000, 334 ZSTD_c_experimentalParam4=1001, 335 ZSTD_c_experimentalParam5=1002, 336 ZSTD_c_experimentalParam6=1003, 337} ZSTD_cParameter; 338</b></pre><BR> 339<pre><b>typedef struct { 340 size_t error; 341 int lowerBound; 342 int upperBound; 343} ZSTD_bounds; 344</b></pre><BR> 345<pre><b>ZSTD_bounds ZSTD_cParam_getBounds(ZSTD_cParameter cParam); 346</b><p> All parameters must belong to an interval with lower and upper bounds, 347 otherwise they will either trigger an error or be automatically clamped. 348 @return : a structure, ZSTD_bounds, which contains 349 - an error status field, which must be tested using ZSTD_isError() 350 - lower and upper bounds, both inclusive 351 352</p></pre><BR> 353 354<pre><b>size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int value); 355</b><p> Set one compression parameter, selected by enum ZSTD_cParameter. 356 All parameters have valid bounds. Bounds can be queried using ZSTD_cParam_getBounds(). 357 Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter). 358 Setting a parameter is generally only possible during frame initialization (before starting compression). 359 Exception : when using multi-threading mode (nbWorkers >= 1), 360 the following parameters can be updated _during_ compression (within same frame): 361 => compressionLevel, hashLog, chainLog, searchLog, minMatch, targetLength and strategy. 362 new parameters will be active for next job only (after a flush()). 363 @return : an error code (which can be tested using ZSTD_isError()). 364 365</p></pre><BR> 366 367<pre><b>size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize); 368</b><p> Total input data size to be compressed as a single frame. 369 Value will be written in frame header, unless if explicitly forbidden using ZSTD_c_contentSizeFlag. 370 This value will also be controlled at end of frame, and trigger an error if not respected. 371 @result : 0, or an error code (which can be tested with ZSTD_isError()). 372 Note 1 : pledgedSrcSize==0 actually means zero, aka an empty frame. 373 In order to mean "unknown content size", pass constant ZSTD_CONTENTSIZE_UNKNOWN. 374 ZSTD_CONTENTSIZE_UNKNOWN is default value for any new frame. 375 Note 2 : pledgedSrcSize is only valid once, for the next frame. 376 It's discarded at the end of the frame, and replaced by ZSTD_CONTENTSIZE_UNKNOWN. 377 Note 3 : Whenever all input data is provided and consumed in a single round, 378 for example with ZSTD_compress2(), 379 or invoking immediately ZSTD_compressStream2(,,,ZSTD_e_end), 380 this value is automatically overridden by srcSize instead. 381 382</p></pre><BR> 383 384<pre><b>typedef enum { 385 ZSTD_reset_session_only = 1, 386 ZSTD_reset_parameters = 2, 387 ZSTD_reset_session_and_parameters = 3 388} ZSTD_ResetDirective; 389</b></pre><BR> 390<pre><b>size_t ZSTD_CCtx_reset(ZSTD_CCtx* cctx, ZSTD_ResetDirective reset); 391</b><p> There are 2 different things that can be reset, independently or jointly : 392 - The session : will stop compressing current frame, and make CCtx ready to start a new one. 393 Useful after an error, or to interrupt any ongoing compression. 394 Any internal data not yet flushed is cancelled. 395 Compression parameters and dictionary remain unchanged. 396 They will be used to compress next frame. 397 Resetting session never fails. 398 - The parameters : changes all parameters back to "default". 399 This removes any reference to any dictionary too. 400 Parameters can only be changed between 2 sessions (i.e. no compression is currently ongoing) 401 otherwise the reset fails, and function returns an error value (which can be tested using ZSTD_isError()) 402 - Both : similar to resetting the session, followed by resetting parameters. 403 404</p></pre><BR> 405 406<pre><b>size_t ZSTD_compress2( ZSTD_CCtx* cctx, 407 void* dst, size_t dstCapacity, 408 const void* src, size_t srcSize); 409</b><p> Behave the same as ZSTD_compressCCtx(), but compression parameters are set using the advanced API. 410 ZSTD_compress2() always starts a new frame. 411 Should cctx hold data from a previously unfinished frame, everything about it is forgotten. 412 - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*() 413 - The function is always blocking, returns when compression is completed. 414 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`. 415 @return : compressed size written into `dst` (<= `dstCapacity), 416 or an error code if it fails (which can be tested using ZSTD_isError()). 417 418</p></pre><BR> 419 420<a name="Chapter6"></a><h2>Advanced decompression API</h2><pre></pre> 421 422<pre><b>typedef enum { 423 424 ZSTD_d_windowLogMax=100, </b>/* Select a size limit (in power of 2) beyond which<b> 425 * the streaming API will refuse to allocate memory buffer 426 * in order to protect the host from unreasonable memory requirements. 427 * This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode. 428 * By default, a decompression context accepts window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT). 429 * Special: value 0 means "use default maximum windowLog". */ 430 431 </b>/* note : additional experimental parameters are also available<b> 432 * within the experimental section of the API. 433 * At the time of this writing, they include : 434 * ZSTD_c_format 435 * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them. 436 * note : never ever use experimentalParam? names directly 437 */ 438 ZSTD_d_experimentalParam1=1000 439 440} ZSTD_dParameter; 441</b></pre><BR> 442<pre><b>ZSTD_bounds ZSTD_dParam_getBounds(ZSTD_dParameter dParam); 443</b><p> All parameters must belong to an interval with lower and upper bounds, 444 otherwise they will either trigger an error or be automatically clamped. 445 @return : a structure, ZSTD_bounds, which contains 446 - an error status field, which must be tested using ZSTD_isError() 447 - both lower and upper bounds, inclusive 448 449</p></pre><BR> 450 451<pre><b>size_t ZSTD_DCtx_setParameter(ZSTD_DCtx* dctx, ZSTD_dParameter param, int value); 452</b><p> Set one compression parameter, selected by enum ZSTD_dParameter. 453 All parameters have valid bounds. Bounds can be queried using ZSTD_dParam_getBounds(). 454 Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter). 455 Setting a parameter is only possible during frame initialization (before starting decompression). 456 @return : 0, or an error code (which can be tested using ZSTD_isError()). 457 458</p></pre><BR> 459 460<pre><b>size_t ZSTD_DCtx_reset(ZSTD_DCtx* dctx, ZSTD_ResetDirective reset); 461</b><p> Return a DCtx to clean state. 462 Session and parameters can be reset jointly or separately. 463 Parameters can only be reset when no active frame is being decompressed. 464 @return : 0, or an error code, which can be tested with ZSTD_isError() 465 466</p></pre><BR> 467 468<a name="Chapter7"></a><h2>Streaming</h2><pre></pre> 469 470<pre><b>typedef struct ZSTD_inBuffer_s { 471 const void* src; </b>/**< start of input buffer */<b> 472 size_t size; </b>/**< size of input buffer */<b> 473 size_t pos; </b>/**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */<b> 474} ZSTD_inBuffer; 475</b></pre><BR> 476<pre><b>typedef struct ZSTD_outBuffer_s { 477 void* dst; </b>/**< start of output buffer */<b> 478 size_t size; </b>/**< size of output buffer */<b> 479 size_t pos; </b>/**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */<b> 480} ZSTD_outBuffer; 481</b></pre><BR> 482<a name="Chapter8"></a><h2>Streaming compression - HowTo</h2><pre> 483 A ZSTD_CStream object is required to track streaming operation. 484 Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources. 485 ZSTD_CStream objects can be reused multiple times on consecutive compression operations. 486 It is recommended to re-use ZSTD_CStream since it will play nicer with system's memory, by re-using already allocated memory. 487 488 For parallel execution, use one separate ZSTD_CStream per thread. 489 490 note : since v1.3.0, ZSTD_CStream and ZSTD_CCtx are the same thing. 491 492 Parameters are sticky : when starting a new compression on the same context, 493 it will re-use the same sticky parameters as previous compression session. 494 When in doubt, it's recommended to fully initialize the context before usage. 495 Use ZSTD_CCtx_reset() to reset the context and ZSTD_CCtx_setParameter(), 496 ZSTD_CCtx_setPledgedSrcSize(), or ZSTD_CCtx_loadDictionary() and friends to 497 set more specific parameters, the pledged source size, or load a dictionary. 498 499 Use ZSTD_compressStream2() with ZSTD_e_continue as many times as necessary to 500 consume input stream. The function will automatically update both `pos` 501 fields within `input` and `output`. 502 Note that the function may not consume the entire input, for example, because 503 the output buffer is already full, in which case `input.pos < input.size`. 504 The caller must check if input has been entirely consumed. 505 If not, the caller must make some room to receive more compressed data, 506 and then present again remaining input data. 507 note: ZSTD_e_continue is guaranteed to make some forward progress when called, 508 but doesn't guarantee maximal forward progress. This is especially relevant 509 when compressing with multiple threads. The call won't block if it can 510 consume some input, but if it can't it will wait for some, but not all, 511 output to be flushed. 512 @return : provides a minimum amount of data remaining to be flushed from internal buffers 513 or an error code, which can be tested using ZSTD_isError(). 514 515 At any moment, it's possible to flush whatever data might remain stuck within internal buffer, 516 using ZSTD_compressStream2() with ZSTD_e_flush. `output->pos` will be updated. 517 Note that, if `output->size` is too small, a single invocation with ZSTD_e_flush might not be enough (return code > 0). 518 In which case, make some room to receive more compressed data, and call again ZSTD_compressStream2() with ZSTD_e_flush. 519 You must continue calling ZSTD_compressStream2() with ZSTD_e_flush until it returns 0, at which point you can change the 520 operation. 521 note: ZSTD_e_flush will flush as much output as possible, meaning when compressing with multiple threads, it will 522 block until the flush is complete or the output buffer is full. 523 @return : 0 if internal buffers are entirely flushed, 524 >0 if some data still present within internal buffer (the value is minimal estimation of remaining size), 525 or an error code, which can be tested using ZSTD_isError(). 526 527 Calling ZSTD_compressStream2() with ZSTD_e_end instructs to finish a frame. 528 It will perform a flush and write frame epilogue. 529 The epilogue is required for decoders to consider a frame completed. 530 flush operation is the same, and follows same rules as calling ZSTD_compressStream2() with ZSTD_e_flush. 531 You must continue calling ZSTD_compressStream2() with ZSTD_e_end until it returns 0, at which point you are free to 532 start a new frame. 533 note: ZSTD_e_end will flush as much output as possible, meaning when compressing with multiple threads, it will 534 block until the flush is complete or the output buffer is full. 535 @return : 0 if frame fully completed and fully flushed, 536 >0 if some data still present within internal buffer (the value is minimal estimation of remaining size), 537 or an error code, which can be tested using ZSTD_isError(). 538 539 540<BR></pre> 541 542<pre><b>typedef ZSTD_CCtx ZSTD_CStream; </b>/**< CCtx and CStream are now effectively same object (>= v1.3.0) */<b> 543</b></pre><BR> 544<h3>ZSTD_CStream management functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream(void); 545size_t ZSTD_freeCStream(ZSTD_CStream* zcs); 546</pre></b><BR> 547<h3>Streaming compression functions</h3><pre></pre><b><pre>typedef enum { 548 ZSTD_e_continue=0, </b>/* collect more data, encoder decides when to output compressed result, for optimal compression ratio */<b> 549 ZSTD_e_flush=1, </b>/* flush any data provided so far,<b> 550 * it creates (at least) one new block, that can be decoded immediately on reception; 551 * frame will continue: any future data can still reference previously compressed data, improving compression. 552 * note : multithreaded compression will block to flush as much output as possible. */ 553 ZSTD_e_end=2 </b>/* flush any remaining data _and_ close current frame.<b> 554 * note that frame is only closed after compressed data is fully flushed (return value == 0). 555 * After that point, any additional data starts a new frame. 556 * note : each frame is independent (does not reference any content from previous frame). 557 : note : multithreaded compression will block to flush as much output as possible. */ 558} ZSTD_EndDirective; 559</pre></b><BR> 560<pre><b>size_t ZSTD_compressStream2( ZSTD_CCtx* cctx, 561 ZSTD_outBuffer* output, 562 ZSTD_inBuffer* input, 563 ZSTD_EndDirective endOp); 564</b><p> Behaves about the same as ZSTD_compressStream, with additional control on end directive. 565 - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*() 566 - Compression parameters cannot be changed once compression is started (save a list of exceptions in multi-threading mode) 567 - output->pos must be <= dstCapacity, input->pos must be <= srcSize 568 - output->pos and input->pos will be updated. They are guaranteed to remain below their respective limit. 569 - When nbWorkers==0 (default), function is blocking : it completes its job before returning to caller. 570 - 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, 571 and then immediately returns, just indicating that there is some data remaining to be flushed. 572 The function nonetheless guarantees forward progress : it will return only after it reads or write at least 1+ byte. 573 - 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. 574 - @return provides a minimum amount of data remaining to be flushed from internal buffers 575 or an error code, which can be tested using ZSTD_isError(). 576 if @return != 0, flush is not fully completed, there is still some data left within internal buffers. 577 This is useful for ZSTD_e_flush, since in this case more flushes are necessary to empty all buffers. 578 For ZSTD_e_end, @return == 0 when internal buffers are fully flushed and frame is completed. 579 - after a ZSTD_e_end directive, if internal buffer is not fully flushed (@return != 0), 580 only ZSTD_e_end or ZSTD_e_flush operations are allowed. 581 Before starting a new compression job, or changing compression parameters, 582 it is required to fully flush internal buffers. 583 584</p></pre><BR> 585 586<pre><b>size_t ZSTD_CStreamInSize(void); </b>/**< recommended size for input buffer */<b> 587</b></pre><BR> 588<pre><b>size_t ZSTD_CStreamOutSize(void); </b>/**< recommended size for output buffer. Guarantee to successfully flush at least one complete compressed block. */<b> 589</b></pre><BR> 590<pre><b>size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel); 591</b>/*!<b> 592 * Alternative for ZSTD_compressStream2(zcs, output, input, ZSTD_e_continue). 593 * NOTE: The return value is different. ZSTD_compressStream() returns a hint for 594 * the next read size (if non-zero and not an error). ZSTD_compressStream2() 595 * returns the minimum nb of bytes left to flush (if non-zero and not an error). 596 */ 597size_t ZSTD_compressStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input); 598</b>/*! Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_flush). */<b> 599size_t ZSTD_flushStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output); 600</b>/*! Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_end). */<b> 601size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output); 602</b><p> 603 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 604 ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any) 605 ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel); 606 607</p></pre><BR> 608 609<a name="Chapter9"></a><h2>Streaming decompression - HowTo</h2><pre> 610 A ZSTD_DStream object is required to track streaming operations. 611 Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources. 612 ZSTD_DStream objects can be re-used multiple times. 613 614 Use ZSTD_initDStream() to start a new decompression operation. 615 @return : recommended first input size 616 Alternatively, use advanced API to set specific properties. 617 618 Use ZSTD_decompressStream() repetitively to consume your input. 619 The function will update both `pos` fields. 620 If `input.pos < input.size`, some input has not been consumed. 621 It's up to the caller to present again remaining data. 622 The function tries to flush all data decoded immediately, respecting output buffer size. 623 If `output.pos < output.size`, decoder has flushed everything it could. 624 But if `output.pos == output.size`, there might be some data left within internal buffers., 625 In which case, call ZSTD_decompressStream() again to flush whatever remains in the buffer. 626 Note : with no additional input provided, amount of data flushed is necessarily <= ZSTD_BLOCKSIZE_MAX. 627 @return : 0 when a frame is completely decoded and fully flushed, 628 or an error code, which can be tested using ZSTD_isError(), 629 or any other value > 0, which means there is still some decoding or flushing to do to complete current frame : 630 the return value is a suggested next input size (just a hint for better latency) 631 that will never request more than the remaining frame size. 632 633<BR></pre> 634 635<pre><b>typedef ZSTD_DCtx ZSTD_DStream; </b>/**< DCtx and DStream are now effectively same object (>= v1.3.0) */<b> 636</b></pre><BR> 637<h3>ZSTD_DStream management functions</h3><pre></pre><b><pre>ZSTD_DStream* ZSTD_createDStream(void); 638size_t ZSTD_freeDStream(ZSTD_DStream* zds); 639</pre></b><BR> 640<h3>Streaming decompression functions</h3><pre></pre><b><pre></pre></b><BR> 641<pre><b>size_t ZSTD_DStreamInSize(void); </b>/*!< recommended size for input buffer */<b> 642</b></pre><BR> 643<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> 644</b></pre><BR> 645<a name="Chapter10"></a><h2>Simple dictionary API</h2><pre></pre> 646 647<pre><b>size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx, 648 void* dst, size_t dstCapacity, 649 const void* src, size_t srcSize, 650 const void* dict,size_t dictSize, 651 int compressionLevel); 652</b><p> Compression at an explicit compression level using a Dictionary. 653 A dictionary can be any arbitrary data segment (also called a prefix), 654 or a buffer with specified information (see dictBuilder/zdict.h). 655 Note : This function loads the dictionary, resulting in significant startup delay. 656 It's intended for a dictionary used only once. 657 Note 2 : When `dict == NULL || dictSize < 8` no dictionary is used. 658</p></pre><BR> 659 660<pre><b>size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx, 661 void* dst, size_t dstCapacity, 662 const void* src, size_t srcSize, 663 const void* dict,size_t dictSize); 664</b><p> Decompression using a known Dictionary. 665 Dictionary must be identical to the one used during compression. 666 Note : This function loads the dictionary, resulting in significant startup delay. 667 It's intended for a dictionary used only once. 668 Note : When `dict == NULL || dictSize < 8` no dictionary is used. 669</p></pre><BR> 670 671<a name="Chapter11"></a><h2>Bulk processing dictionary API</h2><pre></pre> 672 673<pre><b>ZSTD_CDict* ZSTD_createCDict(const void* dictBuffer, size_t dictSize, 674 int compressionLevel); 675</b><p> When compressing multiple messages / blocks using the same dictionary, it's recommended to load it only once. 676 ZSTD_createCDict() will create a digested dictionary, ready to start future compression operations without startup cost. 677 ZSTD_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only. 678 `dictBuffer` can be released after ZSTD_CDict creation, because its content is copied within CDict. 679 Consider experimental function `ZSTD_createCDict_byReference()` if you prefer to not duplicate `dictBuffer` content. 680 Note : A ZSTD_CDict can be created from an empty dictBuffer, but it is inefficient when used to compress small data. 681</p></pre><BR> 682 683<pre><b>size_t ZSTD_freeCDict(ZSTD_CDict* CDict); 684</b><p> Function frees memory allocated by ZSTD_createCDict(). 685</p></pre><BR> 686 687<pre><b>size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx, 688 void* dst, size_t dstCapacity, 689 const void* src, size_t srcSize, 690 const ZSTD_CDict* cdict); 691</b><p> Compression using a digested Dictionary. 692 Recommended when same dictionary is used multiple times. 693 Note : compression level is _decided at dictionary creation time_, 694 and frame parameters are hardcoded (dictID=yes, contentSize=yes, checksum=no) 695</p></pre><BR> 696 697<pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dictBuffer, size_t dictSize); 698</b><p> Create a digested dictionary, ready to start decompression operation without startup delay. 699 dictBuffer can be released after DDict creation, as its content is copied inside DDict. 700</p></pre><BR> 701 702<pre><b>size_t ZSTD_freeDDict(ZSTD_DDict* ddict); 703</b><p> Function frees memory allocated with ZSTD_createDDict() 704</p></pre><BR> 705 706<pre><b>size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx, 707 void* dst, size_t dstCapacity, 708 const void* src, size_t srcSize, 709 const ZSTD_DDict* ddict); 710</b><p> Decompression using a digested Dictionary. 711 Recommended when same dictionary is used multiple times. 712</p></pre><BR> 713 714<a name="Chapter12"></a><h2>Dictionary helper functions</h2><pre></pre> 715 716<pre><b>unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize); 717</b><p> Provides the dictID stored within dictionary. 718 if @return == 0, the dictionary is not conformant with Zstandard specification. 719 It can still be loaded, but as a content-only dictionary. 720</p></pre><BR> 721 722<pre><b>unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict); 723</b><p> Provides the dictID of the dictionary loaded into `ddict`. 724 If @return == 0, the dictionary is not conformant to Zstandard specification, or empty. 725 Non-conformant dictionaries can still be loaded, but as content-only dictionaries. 726</p></pre><BR> 727 728<pre><b>unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize); 729</b><p> Provides the dictID required to decompressed the frame stored within `src`. 730 If @return == 0, the dictID could not be decoded. 731 This could for one of the following reasons : 732 - The frame does not require a dictionary to be decoded (most common case). 733 - The frame was built with dictID intentionally removed. Whatever dictionary is necessary is a hidden information. 734 Note : this use case also happens when using a non-conformant dictionary. 735 - `srcSize` is too small, and as a result, the frame header could not be decoded (only possible if `srcSize < ZSTD_FRAMEHEADERSIZE_MAX`). 736 - This is not a Zstandard frame. 737 When identifying the exact failure cause, it's possible to use ZSTD_getFrameHeader(), which will provide a more precise error code. 738</p></pre><BR> 739 740<a name="Chapter13"></a><h2>Advanced dictionary and prefix API</h2><pre> 741 This API allows dictionaries to be used with ZSTD_compress2(), 742 ZSTD_compressStream2(), and ZSTD_decompress(). Dictionaries are sticky, and 743 only reset with the context is reset with ZSTD_reset_parameters or 744 ZSTD_reset_session_and_parameters. Prefixes are single-use. 745<BR></pre> 746 747<pre><b>size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize); 748</b><p> Create an internal CDict from `dict` buffer. 749 Decompression will have to use same dictionary. 750 @result : 0, or an error code (which can be tested with ZSTD_isError()). 751 Special: Loading a NULL (or 0-size) dictionary invalidates previous dictionary, 752 meaning "return to no-dictionary mode". 753 Note 1 : Dictionary is sticky, it will be used for all future compressed frames. 754 To return to "no-dictionary" situation, load a NULL dictionary (or reset parameters). 755 Note 2 : Loading a dictionary involves building tables. 756 It's also a CPU consuming operation, with non-negligible impact on latency. 757 Tables are dependent on compression parameters, and for this reason, 758 compression parameters can no longer be changed after loading a dictionary. 759 Note 3 :`dict` content will be copied internally. 760 Use experimental ZSTD_CCtx_loadDictionary_byReference() to reference content instead. 761 In such a case, dictionary buffer must outlive its users. 762 Note 4 : Use ZSTD_CCtx_loadDictionary_advanced() 763 to precisely select how dictionary content must be interpreted. 764</p></pre><BR> 765 766<pre><b>size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); 767</b><p> Reference a prepared dictionary, to be used for all next compressed frames. 768 Note that compression parameters are enforced from within CDict, 769 and supersede any compression parameter previously set within CCtx. 770 The parameters ignored are labled as "superseded-by-cdict" in the ZSTD_cParameter enum docs. 771 The ignored parameters will be used again if the CCtx is returned to no-dictionary mode. 772 The dictionary will remain valid for future compressed frames using same CCtx. 773 @result : 0, or an error code (which can be tested with ZSTD_isError()). 774 Special : Referencing a NULL CDict means "return to no-dictionary mode". 775 Note 1 : Currently, only one dictionary can be managed. 776 Referencing a new dictionary effectively "discards" any previous one. 777 Note 2 : CDict is just referenced, its lifetime must outlive its usage within CCtx. 778</p></pre><BR> 779 780<pre><b>size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx, 781 const void* prefix, size_t prefixSize); 782</b><p> Reference a prefix (single-usage dictionary) for next compressed frame. 783 A prefix is **only used once**. Tables are discarded at end of frame (ZSTD_e_end). 784 Decompression will need same prefix to properly regenerate data. 785 Compressing with a prefix is similar in outcome as performing a diff and compressing it, 786 but performs much faster, especially during decompression (compression speed is tunable with compression level). 787 @result : 0, or an error code (which can be tested with ZSTD_isError()). 788 Special: Adding any prefix (including NULL) invalidates any previous prefix or dictionary 789 Note 1 : Prefix buffer is referenced. It **must** outlive compression. 790 Its content must remain unmodified during compression. 791 Note 2 : If the intention is to diff some large src data blob with some prior version of itself, 792 ensure that the window size is large enough to contain the entire source. 793 See ZSTD_c_windowLog. 794 Note 3 : Referencing a prefix involves building tables, which are dependent on compression parameters. 795 It's a CPU consuming operation, with non-negligible impact on latency. 796 If there is a need to use the same prefix multiple times, consider loadDictionary instead. 797 Note 4 : By default, the prefix is interpreted as raw content (ZSTD_dm_rawContent). 798 Use experimental ZSTD_CCtx_refPrefix_advanced() to alter dictionary interpretation. 799</p></pre><BR> 800 801<pre><b>size_t ZSTD_DCtx_loadDictionary(ZSTD_DCtx* dctx, const void* dict, size_t dictSize); 802</b><p> Create an internal DDict from dict buffer, 803 to be used to decompress next frames. 804 The dictionary remains valid for all future frames, until explicitly invalidated. 805 @result : 0, or an error code (which can be tested with ZSTD_isError()). 806 Special : Adding a NULL (or 0-size) dictionary invalidates any previous dictionary, 807 meaning "return to no-dictionary mode". 808 Note 1 : Loading a dictionary involves building tables, 809 which has a non-negligible impact on CPU usage and latency. 810 It's recommended to "load once, use many times", to amortize the cost 811 Note 2 :`dict` content will be copied internally, so `dict` can be released after loading. 812 Use ZSTD_DCtx_loadDictionary_byReference() to reference dictionary content instead. 813 Note 3 : Use ZSTD_DCtx_loadDictionary_advanced() to take control of 814 how dictionary content is loaded and interpreted. 815 816</p></pre><BR> 817 818<pre><b>size_t ZSTD_DCtx_refDDict(ZSTD_DCtx* dctx, const ZSTD_DDict* ddict); 819</b><p> Reference a prepared dictionary, to be used to decompress next frames. 820 The dictionary remains active for decompression of future frames using same DCtx. 821 @result : 0, or an error code (which can be tested with ZSTD_isError()). 822 Note 1 : Currently, only one dictionary can be managed. 823 Referencing a new dictionary effectively "discards" any previous one. 824 Special: referencing a NULL DDict means "return to no-dictionary mode". 825 Note 2 : DDict is just referenced, its lifetime must outlive its usage from DCtx. 826 827</p></pre><BR> 828 829<pre><b>size_t ZSTD_DCtx_refPrefix(ZSTD_DCtx* dctx, 830 const void* prefix, size_t prefixSize); 831</b><p> Reference a prefix (single-usage dictionary) to decompress next frame. 832 This is the reverse operation of ZSTD_CCtx_refPrefix(), 833 and must use the same prefix as the one used during compression. 834 Prefix is **only used once**. Reference is discarded at end of frame. 835 End of frame is reached when ZSTD_decompressStream() returns 0. 836 @result : 0, or an error code (which can be tested with ZSTD_isError()). 837 Note 1 : Adding any prefix (including NULL) invalidates any previously set prefix or dictionary 838 Note 2 : Prefix buffer is referenced. It **must** outlive decompression. 839 Prefix buffer must remain unmodified up to the end of frame, 840 reached when ZSTD_decompressStream() returns 0. 841 Note 3 : By default, the prefix is treated as raw content (ZSTD_dm_rawContent). 842 Use ZSTD_CCtx_refPrefix_advanced() to alter dictMode (Experimental section) 843 Note 4 : Referencing a raw content prefix has almost no cpu nor memory cost. 844 A full dictionary is more costly, as it requires building tables. 845 846</p></pre><BR> 847 848<pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx); 849size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx); 850size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs); 851size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds); 852size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict); 853size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict); 854</b><p> These functions give the _current_ memory usage of selected object. 855 Note that object memory usage can evolve (increase or decrease) over time. 856</p></pre><BR> 857 858<a name="Chapter14"></a><h2>experimental API (static linking only)</h2><pre> 859 The following symbols and constants 860 are not planned to join "stable API" status in the near future. 861 They can still change in future versions. 862 Some of them are planned to remain in the static_only section indefinitely. 863 Some of them might be removed in the future (especially when redundant with existing stable functions) 864 865<BR></pre> 866 867<pre><b>typedef struct { 868 unsigned windowLog; </b>/**< largest match distance : larger == more compression, more memory needed during decompression */<b> 869 unsigned chainLog; </b>/**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */<b> 870 unsigned hashLog; </b>/**< dispatch table : larger == faster, more memory */<b> 871 unsigned searchLog; </b>/**< nb of searches : larger == more compression, slower */<b> 872 unsigned minMatch; </b>/**< match length searched : larger == faster decompression, sometimes less compression */<b> 873 unsigned targetLength; </b>/**< acceptable match size for optimal parser (only) : larger == more compression, slower */<b> 874 ZSTD_strategy strategy; </b>/**< see ZSTD_strategy definition above */<b> 875} ZSTD_compressionParameters; 876</b></pre><BR> 877<pre><b>typedef struct { 878 int contentSizeFlag; </b>/**< 1: content size will be in frame header (when known) */<b> 879 int checksumFlag; </b>/**< 1: generate a 32-bits checksum using XXH64 algorithm at end of frame, for error detection */<b> 880 int noDictIDFlag; </b>/**< 1: no dictID will be saved into frame header (dictID is only useful for dictionary compression) */<b> 881} ZSTD_frameParameters; 882</b></pre><BR> 883<pre><b>typedef struct { 884 ZSTD_compressionParameters cParams; 885 ZSTD_frameParameters fParams; 886} ZSTD_parameters; 887</b></pre><BR> 888<pre><b>typedef enum { 889 ZSTD_dct_auto = 0, </b>/* dictionary is "full" when starting with ZSTD_MAGIC_DICTIONARY, otherwise it is "rawContent" */<b> 890 ZSTD_dct_rawContent = 1, </b>/* ensures dictionary is always loaded as rawContent, even if it starts with ZSTD_MAGIC_DICTIONARY */<b> 891 ZSTD_dct_fullDict = 2 </b>/* refuses to load a dictionary if it does not respect Zstandard's specification, starting with ZSTD_MAGIC_DICTIONARY */<b> 892} ZSTD_dictContentType_e; 893</b></pre><BR> 894<pre><b>typedef enum { 895 ZSTD_dlm_byCopy = 0, </b>/**< Copy dictionary content internally */<b> 896 ZSTD_dlm_byRef = 1, </b>/**< Reference dictionary content -- the dictionary buffer must outlive its users. */<b> 897} ZSTD_dictLoadMethod_e; 898</b></pre><BR> 899<pre><b>typedef enum { 900 </b>/* Opened question : should we have a format ZSTD_f_auto ?<b> 901 * Today, it would mean exactly the same as ZSTD_f_zstd1. 902 * But, in the future, should several formats become supported, 903 * on the compression side, it would mean "default format". 904 * On the decompression side, it would mean "automatic format detection", 905 * so that ZSTD_f_zstd1 would mean "accept *only* zstd frames". 906 * Since meaning is a little different, another option could be to define different enums for compression and decompression. 907 * This question could be kept for later, when there are actually multiple formats to support, 908 * but there is also the question of pinning enum values, and pinning value `0` is especially important */ 909 ZSTD_f_zstd1 = 0, </b>/* zstd frame format, specified in zstd_compression_format.md (default) */<b> 910 ZSTD_f_zstd1_magicless = 1, </b>/* Variant of zstd frame format, without initial 4-bytes magic number.<b> 911 * Useful to save 4 bytes per generated frame. 912 * Decoder cannot recognise automatically this format, requiring this instruction. */ 913} ZSTD_format_e; 914</b></pre><BR> 915<pre><b>typedef enum { 916 </b>/* Note: this enum and the behavior it controls are effectively internal<b> 917 * implementation details of the compressor. They are expected to continue 918 * to evolve and should be considered only in the context of extremely 919 * advanced performance tuning. 920 * 921 * Zstd currently supports the use of a CDict in two ways: 922 * 923 * - The contents of the CDict can be copied into the working context. This 924 * means that the compression can search both the dictionary and input 925 * while operating on a single set of internal tables. This makes 926 * the compression faster per-byte of input. However, the initial copy of 927 * the CDict's tables incurs a fixed cost at the beginning of the 928 * compression. For small compressions (< 8 KB), that copy can dominate 929 * the cost of the compression. 930 * 931 * - The CDict's tables can be used in-place. In this model, compression is 932 * slower per input byte, because the compressor has to search two sets of 933 * tables. However, this model incurs no start-up cost (as long as the 934 * working context's tables can be reused). For small inputs, this can be 935 * faster than copying the CDict's tables. 936 * 937 * Zstd has a simple internal heuristic that selects which strategy to use 938 * at the beginning of a compression. However, if experimentation shows that 939 * Zstd is making poor choices, it is possible to override that choice with 940 * this enum. 941 */ 942 ZSTD_dictDefaultAttach = 0, </b>/* Use the default heuristic. */<b> 943 ZSTD_dictForceAttach = 1, </b>/* Never copy the dictionary. */<b> 944 ZSTD_dictForceCopy = 2, </b>/* Always copy the dictionary. */<b> 945} ZSTD_dictAttachPref_e; 946</b></pre><BR> 947<pre><b>typedef enum { 948 ZSTD_lcm_auto = 0, </b>/**< Automatically determine the compression mode based on the compression level.<b> 949 * Negative compression levels will be uncompressed, and positive compression 950 * levels will be compressed. */ 951 ZSTD_lcm_huffman = 1, </b>/**< Always attempt Huffman compression. Uncompressed literals will still be<b> 952 * emitted if Huffman compression is not profitable. */ 953 ZSTD_lcm_uncompressed = 2, </b>/**< Always emit uncompressed literals. */<b> 954} ZSTD_literalCompressionMode_e; 955</b></pre><BR> 956<a name="Chapter15"></a><h2>Frame size functions</h2><pre></pre> 957 958<pre><b>unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize); 959</b><p> `src` should point to the start of a series of ZSTD encoded and/or skippable frames 960 `srcSize` must be the _exact_ size of this series 961 (i.e. there should be a frame boundary at `src + srcSize`) 962 @return : - decompressed size of all data in all successive frames 963 - if the decompressed size cannot be determined: ZSTD_CONTENTSIZE_UNKNOWN 964 - if an error occurred: ZSTD_CONTENTSIZE_ERROR 965 966 note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode. 967 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size. 968 In which case, it's necessary to use streaming mode to decompress data. 969 note 2 : decompressed size is always present when compression is done with ZSTD_compress() 970 note 3 : decompressed size can be very large (64-bits value), 971 potentially larger than what local system can handle as a single memory segment. 972 In which case, it's necessary to use streaming mode to decompress data. 973 note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified. 974 Always ensure result fits within application's authorized limits. 975 Each application can set its own limits. 976 note 5 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to 977 read each contained frame header. This is fast as most of the data is skipped, 978 however it does mean that all frame data must be present and valid. 979</p></pre><BR> 980 981<pre><b>unsigned long long ZSTD_decompressBound(const void* src, size_t srcSize); 982</b><p> `src` should point to the start of a series of ZSTD encoded and/or skippable frames 983 `srcSize` must be the _exact_ size of this series 984 (i.e. there should be a frame boundary at `src + srcSize`) 985 @return : - upper-bound for the decompressed size of all data in all successive frames 986 - if an error occured: ZSTD_CONTENTSIZE_ERROR 987 988 note 1 : an error can occur if `src` contains an invalid or incorrectly formatted frame. 989 note 2 : the upper-bound is exact when the decompressed size field is available in every ZSTD encoded frame of `src`. 990 in this case, `ZSTD_findDecompressedSize` and `ZSTD_decompressBound` return the same value. 991 note 3 : when the decompressed size field isn't available, the upper-bound for that frame is calculated by: 992 upper-bound = # blocks * min(128 KB, Window_Size) 993 994</p></pre><BR> 995 996<pre><b>size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize); 997</b><p> srcSize must be >= ZSTD_FRAMEHEADERSIZE_PREFIX. 998 @return : size of the Frame Header, 999 or an error code (if srcSize is too small) 1000</p></pre><BR> 1001 1002<a name="Chapter16"></a><h2>Memory management</h2><pre></pre> 1003 1004<pre><b>size_t ZSTD_estimateCCtxSize(int compressionLevel); 1005size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams); 1006size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params); 1007size_t ZSTD_estimateDCtxSize(void); 1008</b><p> These functions make it possible to estimate memory usage 1009 of a future {D,C}Ctx, before its creation. 1010 ZSTD_estimateCCtxSize() will provide a budget large enough for any compression level up to selected one. 1011 It will also consider src size to be arbitrarily "large", which is worst case. 1012 If srcSize is known to always be small, ZSTD_estimateCCtxSize_usingCParams() can provide a tighter estimation. 1013 ZSTD_estimateCCtxSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel. 1014 ZSTD_estimateCCtxSize_usingCCtxParams() can be used in tandem with ZSTD_CCtxParams_setParameter(). Only single-threaded compression is supported. This function will return an error code if ZSTD_c_nbWorkers is >= 1. 1015 Note : CCtx size estimation is only correct for single-threaded compression. 1016</p></pre><BR> 1017 1018<pre><b>size_t ZSTD_estimateCStreamSize(int compressionLevel); 1019size_t ZSTD_estimateCStreamSize_usingCParams(ZSTD_compressionParameters cParams); 1020size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params); 1021size_t ZSTD_estimateDStreamSize(size_t windowSize); 1022size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize); 1023</b><p> ZSTD_estimateCStreamSize() will provide a budget large enough for any compression level up to selected one. 1024 It will also consider src size to be arbitrarily "large", which is worst case. 1025 If srcSize is known to always be small, ZSTD_estimateCStreamSize_usingCParams() can provide a tighter estimation. 1026 ZSTD_estimateCStreamSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel. 1027 ZSTD_estimateCStreamSize_usingCCtxParams() can be used in tandem with ZSTD_CCtxParams_setParameter(). Only single-threaded compression is supported. This function will return an error code if ZSTD_c_nbWorkers is >= 1. 1028 Note : CStream size estimation is only correct for single-threaded compression. 1029 ZSTD_DStream memory budget depends on window Size. 1030 This information can be passed manually, using ZSTD_estimateDStreamSize, 1031 or deducted from a valid frame Header, using ZSTD_estimateDStreamSize_fromFrame(); 1032 Note : if streaming is init with function ZSTD_init?Stream_usingDict(), 1033 an internal ?Dict will be created, which additional size is not estimated here. 1034 In this case, get total size by adding ZSTD_estimate?DictSize 1035</p></pre><BR> 1036 1037<pre><b>size_t ZSTD_estimateCDictSize(size_t dictSize, int compressionLevel); 1038size_t ZSTD_estimateCDictSize_advanced(size_t dictSize, ZSTD_compressionParameters cParams, ZSTD_dictLoadMethod_e dictLoadMethod); 1039size_t ZSTD_estimateDDictSize(size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod); 1040</b><p> ZSTD_estimateCDictSize() will bet that src size is relatively "small", and content is copied, like ZSTD_createCDict(). 1041 ZSTD_estimateCDictSize_advanced() makes it possible to control compression parameters precisely, like ZSTD_createCDict_advanced(). 1042 Note : dictionaries created by reference (`ZSTD_dlm_byRef`) are logically smaller. 1043 1044</p></pre><BR> 1045 1046<pre><b>ZSTD_CCtx* ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize); 1047ZSTD_CStream* ZSTD_initStaticCStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticCCtx() */<b> 1048</b><p> Initialize an object using a pre-allocated fixed-size buffer. 1049 workspace: The memory area to emplace the object into. 1050 Provided pointer *must be 8-bytes aligned*. 1051 Buffer must outlive object. 1052 workspaceSize: Use ZSTD_estimate*Size() to determine 1053 how large workspace must be to support target scenario. 1054 @return : pointer to object (same address as workspace, just different type), 1055 or NULL if error (size too small, incorrect alignment, etc.) 1056 Note : zstd will never resize nor malloc() when using a static buffer. 1057 If the object requires more memory than available, 1058 zstd will just error out (typically ZSTD_error_memory_allocation). 1059 Note 2 : there is no corresponding "free" function. 1060 Since workspace is allocated externally, it must be freed externally too. 1061 Note 3 : cParams : use ZSTD_getCParams() to convert a compression level 1062 into its associated cParams. 1063 Limitation 1 : currently not compatible with internal dictionary creation, triggered by 1064 ZSTD_CCtx_loadDictionary(), ZSTD_initCStream_usingDict() or ZSTD_initDStream_usingDict(). 1065 Limitation 2 : static cctx currently not compatible with multi-threading. 1066 Limitation 3 : static dctx is incompatible with legacy support. 1067 1068</p></pre><BR> 1069 1070<pre><b>ZSTD_DStream* ZSTD_initStaticDStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticDCtx() */<b> 1071</b></pre><BR> 1072<pre><b>typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size); 1073typedef void (*ZSTD_freeFunction) (void* opaque, void* address); 1074typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem; 1075static ZSTD_customMem const ZSTD_defaultCMem = { NULL, NULL, NULL }; </b>/**< this constant defers to stdlib's functions */<b> 1076</b><p> These prototypes make it possible to pass your own allocation/free functions. 1077 ZSTD_customMem is provided at creation time, using ZSTD_create*_advanced() variants listed below. 1078 All allocation/free operations will be completed using these custom variants instead of regular <stdlib.h> ones. 1079 1080</p></pre><BR> 1081 1082<a name="Chapter17"></a><h2>Advanced compression functions</h2><pre></pre> 1083 1084<pre><b>ZSTD_CDict* ZSTD_createCDict_byReference(const void* dictBuffer, size_t dictSize, int compressionLevel); 1085</b><p> Create a digested dictionary for compression 1086 Dictionary content is just referenced, not duplicated. 1087 As a consequence, `dictBuffer` **must** outlive CDict, 1088 and its content must remain unmodified throughout the lifetime of CDict. 1089</p></pre><BR> 1090 1091<pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize); 1092</b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize. 1093 `estimatedSrcSize` value is optional, select 0 if not known 1094</p></pre><BR> 1095 1096<pre><b>ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize); 1097</b><p> same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`. 1098 All fields of `ZSTD_frameParameters` are set to default : contentSize=1, checksum=0, noDictID=0 1099</p></pre><BR> 1100 1101<pre><b>size_t ZSTD_checkCParams(ZSTD_compressionParameters params); 1102</b><p> Ensure param values remain within authorized range. 1103 @return 0 on success, or an error code (can be checked with ZSTD_isError()) 1104</p></pre><BR> 1105 1106<pre><b>ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize); 1107</b><p> optimize params for a given `srcSize` and `dictSize`. 1108 `srcSize` can be unknown, in which case use ZSTD_CONTENTSIZE_UNKNOWN. 1109 `dictSize` must be `0` when there is no dictionary. 1110 cPar can be invalid : all parameters will be clamped within valid range in the @return struct. 1111 This function never fails (wide contract) 1112</p></pre><BR> 1113 1114<pre><b>size_t ZSTD_compress_advanced(ZSTD_CCtx* cctx, 1115 void* dst, size_t dstCapacity, 1116 const void* src, size_t srcSize, 1117 const void* dict,size_t dictSize, 1118 ZSTD_parameters params); 1119</b><p> Same as ZSTD_compress_usingDict(), with fine-tune control over compression parameters (by structure) 1120</p></pre><BR> 1121 1122<pre><b>size_t ZSTD_compress_usingCDict_advanced(ZSTD_CCtx* cctx, 1123 void* dst, size_t dstCapacity, 1124 const void* src, size_t srcSize, 1125 const ZSTD_CDict* cdict, 1126 ZSTD_frameParameters fParams); 1127</b><p> Same as ZSTD_compress_usingCDict(), with fine-tune control over frame parameters 1128</p></pre><BR> 1129 1130<pre><b>size_t ZSTD_CCtx_loadDictionary_byReference(ZSTD_CCtx* cctx, const void* dict, size_t dictSize); 1131</b><p> Same as ZSTD_CCtx_loadDictionary(), but dictionary content is referenced, instead of being copied into CCtx. 1132 It saves some memory, but also requires that `dict` outlives its usage within `cctx` 1133</p></pre><BR> 1134 1135<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); 1136</b><p> Same as ZSTD_CCtx_loadDictionary(), but gives finer control over 1137 how to load the dictionary (by copy ? by reference ?) 1138 and how to interpret it (automatic ? force raw mode ? full mode only ?) 1139</p></pre><BR> 1140 1141<pre><b>size_t ZSTD_CCtx_refPrefix_advanced(ZSTD_CCtx* cctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType); 1142</b><p> Same as ZSTD_CCtx_refPrefix(), but gives finer control over 1143 how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?) 1144</p></pre><BR> 1145 1146<pre><b>size_t ZSTD_CCtx_getParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int* value); 1147</b><p> Get the requested compression parameter value, selected by enum ZSTD_cParameter, 1148 and store it into int* value. 1149 @return : 0, or an error code (which can be tested with ZSTD_isError()). 1150 1151</p></pre><BR> 1152 1153<pre><b>ZSTD_CCtx_params* ZSTD_createCCtxParams(void); 1154size_t ZSTD_freeCCtxParams(ZSTD_CCtx_params* params); 1155</b><p> Quick howto : 1156 - ZSTD_createCCtxParams() : Create a ZSTD_CCtx_params structure 1157 - ZSTD_CCtxParams_setParameter() : Push parameters one by one into 1158 an existing ZSTD_CCtx_params structure. 1159 This is similar to 1160 ZSTD_CCtx_setParameter(). 1161 - ZSTD_CCtx_setParametersUsingCCtxParams() : Apply parameters to 1162 an existing CCtx. 1163 These parameters will be applied to 1164 all subsequent frames. 1165 - ZSTD_compressStream2() : Do compression using the CCtx. 1166 - ZSTD_freeCCtxParams() : Free the memory. 1167 1168 This can be used with ZSTD_estimateCCtxSize_advanced_usingCCtxParams() 1169 for static allocation of CCtx for single-threaded compression. 1170 1171</p></pre><BR> 1172 1173<pre><b>size_t ZSTD_CCtxParams_reset(ZSTD_CCtx_params* params); 1174</b><p> Reset params to default values. 1175 1176</p></pre><BR> 1177 1178<pre><b>size_t ZSTD_CCtxParams_init(ZSTD_CCtx_params* cctxParams, int compressionLevel); 1179</b><p> Initializes the compression parameters of cctxParams according to 1180 compression level. All other parameters are reset to their default values. 1181 1182</p></pre><BR> 1183 1184<pre><b>size_t ZSTD_CCtxParams_init_advanced(ZSTD_CCtx_params* cctxParams, ZSTD_parameters params); 1185</b><p> Initializes the compression and frame parameters of cctxParams according to 1186 params. All other parameters are reset to their default values. 1187 1188</p></pre><BR> 1189 1190<pre><b>size_t ZSTD_CCtxParams_setParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int value); 1191</b><p> Similar to ZSTD_CCtx_setParameter. 1192 Set one compression parameter, selected by enum ZSTD_cParameter. 1193 Parameters must be applied to a ZSTD_CCtx using ZSTD_CCtx_setParametersUsingCCtxParams(). 1194 @result : 0, or an error code (which can be tested with ZSTD_isError()). 1195 1196</p></pre><BR> 1197 1198<pre><b>size_t ZSTD_CCtxParams_getParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int* value); 1199</b><p> Similar to ZSTD_CCtx_getParameter. 1200 Get the requested value of one compression parameter, selected by enum ZSTD_cParameter. 1201 @result : 0, or an error code (which can be tested with ZSTD_isError()). 1202 1203</p></pre><BR> 1204 1205<pre><b>size_t ZSTD_CCtx_setParametersUsingCCtxParams( 1206 ZSTD_CCtx* cctx, const ZSTD_CCtx_params* params); 1207</b><p> Apply a set of ZSTD_CCtx_params to the compression context. 1208 This can be done even after compression is started, 1209 if nbWorkers==0, this will have no impact until a new compression is started. 1210 if nbWorkers>=1, new parameters will be picked up at next job, 1211 with a few restrictions (windowLog, pledgedSrcSize, nbWorkers, jobSize, and overlapLog are not updated). 1212 1213</p></pre><BR> 1214 1215<pre><b>size_t ZSTD_compressStream2_simpleArgs ( 1216 ZSTD_CCtx* cctx, 1217 void* dst, size_t dstCapacity, size_t* dstPos, 1218 const void* src, size_t srcSize, size_t* srcPos, 1219 ZSTD_EndDirective endOp); 1220</b><p> Same as ZSTD_compressStream2(), 1221 but using only integral types as arguments. 1222 This variant might be helpful for binders from dynamic languages 1223 which have troubles handling structures containing memory pointers. 1224 1225</p></pre><BR> 1226 1227<a name="Chapter18"></a><h2>Advanced decompression functions</h2><pre></pre> 1228 1229<pre><b>unsigned ZSTD_isFrame(const void* buffer, size_t size); 1230</b><p> Tells if the content of `buffer` starts with a valid Frame Identifier. 1231 Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0. 1232 Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled. 1233 Note 3 : Skippable Frame Identifiers are considered valid. 1234</p></pre><BR> 1235 1236<pre><b>ZSTD_DDict* ZSTD_createDDict_byReference(const void* dictBuffer, size_t dictSize); 1237</b><p> Create a digested dictionary, ready to start decompression operation without startup delay. 1238 Dictionary content is referenced, and therefore stays in dictBuffer. 1239 It is important that dictBuffer outlives DDict, 1240 it must remain read accessible throughout the lifetime of DDict 1241</p></pre><BR> 1242 1243<pre><b>size_t ZSTD_DCtx_loadDictionary_byReference(ZSTD_DCtx* dctx, const void* dict, size_t dictSize); 1244</b><p> Same as ZSTD_DCtx_loadDictionary(), 1245 but references `dict` content instead of copying it into `dctx`. 1246 This saves memory if `dict` remains around., 1247 However, it's imperative that `dict` remains accessible (and unmodified) while being used, so it must outlive decompression. 1248</p></pre><BR> 1249 1250<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); 1251</b><p> Same as ZSTD_DCtx_loadDictionary(), 1252 but gives direct control over 1253 how to load the dictionary (by copy ? by reference ?) 1254 and how to interpret it (automatic ? force raw mode ? full mode only ?). 1255</p></pre><BR> 1256 1257<pre><b>size_t ZSTD_DCtx_refPrefix_advanced(ZSTD_DCtx* dctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType); 1258</b><p> Same as ZSTD_DCtx_refPrefix(), but gives finer control over 1259 how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?) 1260</p></pre><BR> 1261 1262<pre><b>size_t ZSTD_DCtx_setMaxWindowSize(ZSTD_DCtx* dctx, size_t maxWindowSize); 1263</b><p> Refuses allocating internal buffers for frames requiring a window size larger than provided limit. 1264 This protects a decoder context from reserving too much memory for itself (potential attack scenario). 1265 This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode. 1266 By default, a decompression context accepts all window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT) 1267 @return : 0, or an error code (which can be tested using ZSTD_isError()). 1268 1269</p></pre><BR> 1270 1271<pre><b>size_t ZSTD_DCtx_setFormat(ZSTD_DCtx* dctx, ZSTD_format_e format); 1272</b><p> Instruct the decoder context about what kind of data to decode next. 1273 This instruction is mandatory to decode data without a fully-formed header, 1274 such ZSTD_f_zstd1_magicless for example. 1275 @return : 0, or an error code (which can be tested using ZSTD_isError()). 1276</p></pre><BR> 1277 1278<pre><b>size_t ZSTD_decompressStream_simpleArgs ( 1279 ZSTD_DCtx* dctx, 1280 void* dst, size_t dstCapacity, size_t* dstPos, 1281 const void* src, size_t srcSize, size_t* srcPos); 1282</b><p> Same as ZSTD_decompressStream(), 1283 but using only integral types as arguments. 1284 This can be helpful for binders from dynamic languages 1285 which have troubles handling structures containing memory pointers. 1286 1287</p></pre><BR> 1288 1289<a name="Chapter19"></a><h2>Advanced streaming functions</h2><pre> Warning : most of these functions are now redundant with the Advanced API. 1290 Once Advanced API reaches "stable" status, 1291 redundant functions will be deprecated, and then at some point removed. 1292<BR></pre> 1293 1294<h3>Advanced Streaming compression functions</h3><pre></pre><b><pre></b>/**! ZSTD_initCStream_srcSize() :<b> 1295 * This function is deprecated, and equivalent to: 1296 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1297 * ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any) 1298 * ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel); 1299 * ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1300 * 1301 * pledgedSrcSize must be correct. If it is not known at init time, use 1302 * ZSTD_CONTENTSIZE_UNKNOWN. Note that, for compatibility with older programs, 1303 * "0" also disables frame content size field. It may be enabled in the future. 1304 */ 1305size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize); 1306</b>/**! ZSTD_initCStream_usingDict() :<b> 1307 * This function is deprecated, and is equivalent to: 1308 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1309 * ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel); 1310 * ZSTD_CCtx_loadDictionary(zcs, dict, dictSize); 1311 * 1312 * Creates of an internal CDict (incompatible with static CCtx), except if 1313 * dict == NULL or dictSize < 8, in which case no dict is used. 1314 * Note: dict is loaded with ZSTD_dm_auto (treated as a full zstd dictionary if 1315 * it begins with ZSTD_MAGIC_DICTIONARY, else as raw content) and ZSTD_dlm_byCopy. 1316 */ 1317size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); 1318</b>/**! ZSTD_initCStream_advanced() :<b> 1319 * This function is deprecated, and is approximately equivalent to: 1320 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1321 * ZSTD_CCtx_setZstdParams(zcs, params); // Set the zstd params and leave the rest as-is 1322 * ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1323 * ZSTD_CCtx_loadDictionary(zcs, dict, dictSize); 1324 * 1325 * pledgedSrcSize must be correct. If srcSize is not known at init time, use 1326 * value ZSTD_CONTENTSIZE_UNKNOWN. dict is loaded with ZSTD_dm_auto and ZSTD_dlm_byCopy. 1327 */ 1328size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize, 1329 ZSTD_parameters params, unsigned long long pledgedSrcSize); 1330</b>/**! ZSTD_initCStream_usingCDict() :<b> 1331 * This function is deprecated, and equivalent to: 1332 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1333 * ZSTD_CCtx_refCDict(zcs, cdict); 1334 * 1335 * note : cdict will just be referenced, and must outlive compression session 1336 */ 1337size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict); 1338</b>/**! ZSTD_initCStream_usingCDict_advanced() :<b> 1339 * This function is deprecated, and is approximately equivalent to: 1340 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1341 * ZSTD_CCtx_setZstdFrameParams(zcs, fParams); // Set the zstd frame params and leave the rest as-is 1342 * ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1343 * ZSTD_CCtx_refCDict(zcs, cdict); 1344 * 1345 * same as ZSTD_initCStream_usingCDict(), with control over frame parameters. 1346 * pledgedSrcSize must be correct. If srcSize is not known at init time, use 1347 * value ZSTD_CONTENTSIZE_UNKNOWN. 1348 */ 1349size_t ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs, const ZSTD_CDict* cdict, ZSTD_frameParameters fParams, unsigned long long pledgedSrcSize); 1350</pre></b><BR> 1351<pre><b>size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize); 1352</b><p> This function is deprecated, and is equivalent to: 1353 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1354 ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1355 1356 start a new frame, using same parameters from previous frame. 1357 This is typically useful to skip dictionary loading stage, since it will re-use it in-place. 1358 Note that zcs must be init at least once before using ZSTD_resetCStream(). 1359 If pledgedSrcSize is not known at reset time, use macro ZSTD_CONTENTSIZE_UNKNOWN. 1360 If pledgedSrcSize > 0, its value must be correct, as it will be written in header, and controlled at the end. 1361 For the time being, pledgedSrcSize==0 is interpreted as "srcSize unknown" for compatibility with older programs, 1362 but it will change to mean "empty" in future version, so use macro ZSTD_CONTENTSIZE_UNKNOWN instead. 1363 @return : 0, or an error code (which can be tested using ZSTD_isError()) 1364 1365</p></pre><BR> 1366 1367<pre><b>typedef struct { 1368 unsigned long long ingested; </b>/* nb input bytes read and buffered */<b> 1369 unsigned long long consumed; </b>/* nb input bytes actually compressed */<b> 1370 unsigned long long produced; </b>/* nb of compressed bytes generated and buffered */<b> 1371 unsigned long long flushed; </b>/* nb of compressed bytes flushed : not provided; can be tracked from caller side */<b> 1372 unsigned currentJobID; </b>/* MT only : latest started job nb */<b> 1373 unsigned nbActiveWorkers; </b>/* MT only : nb of workers actively compressing at probe time */<b> 1374} ZSTD_frameProgression; 1375</b></pre><BR> 1376<pre><b>size_t ZSTD_toFlushNow(ZSTD_CCtx* cctx); 1377</b><p> Tell how many bytes are ready to be flushed immediately. 1378 Useful for multithreading scenarios (nbWorkers >= 1). 1379 Probe the oldest active job, defined as oldest job not yet entirely flushed, 1380 and check its output buffer. 1381 @return : amount of data stored in oldest job and ready to be flushed immediately. 1382 if @return == 0, it means either : 1383 + there is no active job (could be checked with ZSTD_frameProgression()), or 1384 + oldest job is still actively compressing data, 1385 but everything it has produced has also been flushed so far, 1386 therefore flush speed is limited by production speed of oldest job 1387 irrespective of the speed of concurrent (and newer) jobs. 1388 1389</p></pre><BR> 1390 1391<h3>Advanced Streaming decompression functions</h3><pre></pre><b><pre></b>/**<b> 1392 * This function is deprecated, and is equivalent to: 1393 * 1394 * ZSTD_DCtx_reset(zds, ZSTD_reset_session_only); 1395 * ZSTD_DCtx_loadDictionary(zds, dict, dictSize); 1396 * 1397 * note: no dictionary will be used if dict == NULL or dictSize < 8 1398 */ 1399size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize); 1400</b>/**<b> 1401 * This function is deprecated, and is equivalent to: 1402 * 1403 * ZSTD_DCtx_reset(zds, ZSTD_reset_session_only); 1404 * ZSTD_DCtx_refDDict(zds, ddict); 1405 * 1406 * note : ddict is referenced, it must outlive decompression session 1407 */ 1408size_t ZSTD_initDStream_usingDDict(ZSTD_DStream* zds, const ZSTD_DDict* ddict); 1409</b>/**<b> 1410 * This function is deprecated, and is equivalent to: 1411 * 1412 * ZSTD_DCtx_reset(zds, ZSTD_reset_session_only); 1413 * 1414 * re-use decompression parameters from previous init; saves dictionary loading 1415 */ 1416size_t ZSTD_resetDStream(ZSTD_DStream* zds); 1417</pre></b><BR> 1418<a name="Chapter20"></a><h2>Buffer-less and synchronous inner streaming functions</h2><pre> 1419 This is an advanced API, giving full control over buffer management, for users which need direct control over memory. 1420 But it's also a complex one, with several restrictions, documented below. 1421 Prefer normal streaming API for an easier experience. 1422 1423<BR></pre> 1424 1425<a name="Chapter21"></a><h2>Buffer-less streaming compression (synchronous mode)</h2><pre> 1426 A ZSTD_CCtx object is required to track streaming operations. 1427 Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource. 1428 ZSTD_CCtx object can be re-used multiple times within successive compression operations. 1429 1430 Start by initializing a context. 1431 Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression, 1432 or ZSTD_compressBegin_advanced(), for finer parameter control. 1433 It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx() 1434 1435 Then, consume your input using ZSTD_compressContinue(). 1436 There are some important considerations to keep in mind when using this advanced function : 1437 - ZSTD_compressContinue() has no internal buffer. It uses externally provided buffers only. 1438 - Interface is synchronous : input is consumed entirely and produces 1+ compressed blocks. 1439 - Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario. 1440 Worst case evaluation is provided by ZSTD_compressBound(). 1441 ZSTD_compressContinue() doesn't guarantee recover after a failed compression. 1442 - ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog). 1443 It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks) 1444 - ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps. 1445 In which case, it will "discard" the relevant memory section from its history. 1446 1447 Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum. 1448 It's possible to use srcSize==0, in which case, it will write a final empty block to end the frame. 1449 Without last block mark, frames are considered unfinished (hence corrupted) by compliant decoders. 1450 1451 `ZSTD_CCtx` object can be re-used (ZSTD_compressBegin()) to compress again. 1452<BR></pre> 1453 1454<h3>Buffer-less streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel); 1455size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel); 1456size_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> 1457size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); </b>/**< note: fails if cdict==NULL */<b> 1458size_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> 1459size_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> 1460</pre></b><BR> 1461<a name="Chapter22"></a><h2>Buffer-less streaming decompression (synchronous mode)</h2><pre> 1462 A ZSTD_DCtx object is required to track streaming operations. 1463 Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it. 1464 A ZSTD_DCtx object can be re-used multiple times. 1465 1466 First typical operation is to retrieve frame parameters, using ZSTD_getFrameHeader(). 1467 Frame header is extracted from the beginning of compressed frame, so providing only the frame's beginning is enough. 1468 Data fragment must be large enough to ensure successful decoding. 1469 `ZSTD_frameHeaderSize_max` bytes is guaranteed to always be large enough. 1470 @result : 0 : successful decoding, the `ZSTD_frameHeader` structure is correctly filled. 1471 >0 : `srcSize` is too small, please provide at least @result bytes on next attempt. 1472 errorCode, which can be tested using ZSTD_isError(). 1473 1474 It fills a ZSTD_frameHeader structure with important information to correctly decode the frame, 1475 such as the dictionary ID, content size, or maximum back-reference distance (`windowSize`). 1476 Note that these values could be wrong, either because of data corruption, or because a 3rd party deliberately spoofs false information. 1477 As a consequence, check that values remain within valid application range. 1478 For example, do not allocate memory blindly, check that `windowSize` is within expectation. 1479 Each application can set its own limits, depending on local restrictions. 1480 For extended interoperability, it is recommended to support `windowSize` of at least 8 MB. 1481 1482 ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize` bytes. 1483 ZSTD_decompressContinue() is very sensitive to contiguity, 1484 if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place, 1485 or that previous contiguous segment is large enough to properly handle maximum back-reference distance. 1486 There are multiple ways to guarantee this condition. 1487 1488 The most memory efficient way is to use a round buffer of sufficient size. 1489 Sufficient size is determined by invoking ZSTD_decodingBufferSize_min(), 1490 which can @return an error code if required value is too large for current system (in 32-bits mode). 1491 In a round buffer methodology, ZSTD_decompressContinue() decompresses each block next to previous one, 1492 up to the moment there is not enough room left in the buffer to guarantee decoding another full block, 1493 which maximum size is provided in `ZSTD_frameHeader` structure, field `blockSizeMax`. 1494 At which point, decoding can resume from the beginning of the buffer. 1495 Note that already decoded data stored in the buffer should be flushed before being overwritten. 1496 1497 There are alternatives possible, for example using two or more buffers of size `windowSize` each, though they consume more memory. 1498 1499 Finally, if you control the compression process, you can also ignore all buffer size rules, 1500 as long as the encoder and decoder progress in "lock-step", 1501 aka use exactly the same buffer sizes, break contiguity at the same place, etc. 1502 1503 Once buffers are setup, start decompression, with ZSTD_decompressBegin(). 1504 If decompression requires a dictionary, use ZSTD_decompressBegin_usingDict() or ZSTD_decompressBegin_usingDDict(). 1505 1506 Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively. 1507 ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue(). 1508 ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail. 1509 1510 @result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity). 1511 It can be zero : it just means ZSTD_decompressContinue() has decoded some metadata item. 1512 It can also be an error code, which can be tested with ZSTD_isError(). 1513 1514 A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero. 1515 Context can then be reset to start a new decompression. 1516 1517 Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType(). 1518 This information is not required to properly decode a frame. 1519 1520 == Special case : skippable frames 1521 1522 Skippable frames allow integration of user-defined data into a flow of concatenated frames. 1523 Skippable frames will be ignored (skipped) by decompressor. 1524 The format of skippable frames is as follows : 1525 a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F 1526 b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits 1527 c) Frame Content - any content (User Data) of length equal to Frame Size 1528 For skippable frames ZSTD_getFrameHeader() returns zfhPtr->frameType==ZSTD_skippableFrame. 1529 For skippable frames ZSTD_decompressContinue() always returns 0 : it only skips the content. 1530<BR></pre> 1531 1532<h3>Buffer-less streaming decompression functions</h3><pre></pre><b><pre>typedef enum { ZSTD_frame, ZSTD_skippableFrame } ZSTD_frameType_e; 1533typedef struct { 1534 unsigned long long frameContentSize; </b>/* if == ZSTD_CONTENTSIZE_UNKNOWN, it means this field is not available. 0 means "empty" */<b> 1535 unsigned long long windowSize; </b>/* can be very large, up to <= frameContentSize */<b> 1536 unsigned blockSizeMax; 1537 ZSTD_frameType_e frameType; </b>/* if == ZSTD_skippableFrame, frameContentSize is the size of skippable content */<b> 1538 unsigned headerSize; 1539 unsigned dictID; 1540 unsigned checksumFlag; 1541} ZSTD_frameHeader; 1542</pre></b><BR> 1543<pre><b>size_t ZSTD_getFrameHeader(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize); </b>/**< doesn't consume input */<b> 1544</b>/*! ZSTD_getFrameHeader_advanced() :<b> 1545 * same as ZSTD_getFrameHeader(), 1546 * with added capability to select a format (like ZSTD_f_zstd1_magicless) */ 1547size_t ZSTD_getFrameHeader_advanced(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize, ZSTD_format_e format); 1548size_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> 1549</b><p> decode Frame Header, or requires larger `srcSize`. 1550 @return : 0, `zfhPtr` is correctly filled, 1551 >0, `srcSize` is too small, value is wanted `srcSize` amount, 1552 or an error code, which can be tested using ZSTD_isError() 1553</p></pre><BR> 1554 1555<pre><b>typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e; 1556</b></pre><BR> 1557<a name="Chapter23"></a><h2>Block level API</h2><pre></pre> 1558 1559<pre><b></b><p> Frame metadata cost is typically ~18 bytes, which can be non-negligible for very small blocks (< 100 bytes). 1560 User will have to take in charge required information to regenerate data, such as compressed and content sizes. 1561 1562 A few rules to respect : 1563 - Compressing and decompressing require a context structure 1564 + Use ZSTD_createCCtx() and ZSTD_createDCtx() 1565 - It is necessary to init context before starting 1566 + compression : any ZSTD_compressBegin*() variant, including with dictionary 1567 + decompression : any ZSTD_decompressBegin*() variant, including with dictionary 1568 + copyCCtx() and copyDCtx() can be used too 1569 - Block size is limited, it must be <= ZSTD_getBlockSize() <= ZSTD_BLOCKSIZE_MAX == 128 KB 1570 + If input is larger than a block size, it's necessary to split input data into multiple blocks 1571 + For inputs larger than a single block, really consider using regular ZSTD_compress() instead. 1572 Frame metadata is not that costly, and quickly becomes negligible as source size grows larger. 1573 - When a block is considered not compressible enough, ZSTD_compressBlock() result will be zero. 1574 In which case, nothing is produced into `dst` ! 1575 + User must test for such outcome and deal directly with uncompressed data 1576 + ZSTD_decompressBlock() doesn't accept uncompressed data as input !!! 1577 + In case of multiple successive blocks, should some of them be uncompressed, 1578 decoder must be informed of their existence in order to follow proper history. 1579 Use ZSTD_insertBlock() for such a case. 1580</p></pre><BR> 1581 1582<h3>Raw zstd block functions</h3><pre></pre><b><pre>size_t ZSTD_getBlockSize (const ZSTD_CCtx* cctx); 1583size_t ZSTD_compressBlock (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize); 1584size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize); 1585size_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> 1586</pre></b><BR> 1587</html> 1588</body> 1589