1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 4<title>zstd 1.4.5 Manual</title> 5</head> 6<body> 7<h1>zstd 1.4.5 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">! ZSTD_initCStream_usingDict() :</a></li> 31<li><a href="#Chapter21">! ZSTD_initCStream_advanced() :</a></li> 32<li><a href="#Chapter22">! ZSTD_initCStream_usingCDict() :</a></li> 33<li><a href="#Chapter23">! ZSTD_initCStream_usingCDict_advanced() :</a></li> 34<li><a href="#Chapter24">This function is deprecated, and is equivalent to:</a></li> 35<li><a href="#Chapter25">This function is deprecated, and is equivalent to:</a></li> 36<li><a href="#Chapter26">Buffer-less and synchronous inner streaming functions</a></li> 37<li><a href="#Chapter27">Buffer-less streaming compression (synchronous mode)</a></li> 38<li><a href="#Chapter28">Buffer-less streaming decompression (synchronous mode)</a></li> 39<li><a href="#Chapter29">Block level API</a></li> 40</ol> 41<hr> 42<a name="Chapter1"></a><h2>Introduction</h2><pre> 43 zstd, short for Zstandard, is a fast lossless compression algorithm, targeting 44 real-time compression scenarios at zlib-level and better compression ratios. 45 The zstd compression library provides in-memory compression and decompression 46 functions. 47 48 The library supports regular compression levels from 1 up to ZSTD_maxCLevel(), 49 which is currently 22. Levels >= 20, labeled `--ultra`, should be used with 50 caution, as they require more memory. The library also offers negative 51 compression levels, which extend the range of speed vs. ratio preferences. 52 The lower the level, the faster the speed (at the cost of compression). 53 54 Compression can be done in: 55 - a single step (described as Simple API) 56 - a single step, reusing a context (described as Explicit context) 57 - unbounded multiple steps (described as Streaming compression) 58 59 The compression ratio achievable on small data can be highly improved using 60 a dictionary. Dictionary compression can be performed in: 61 - a single step (described as Simple dictionary API) 62 - a single step, reusing a dictionary (described as Bulk-processing 63 dictionary API) 64 65 Advanced experimental functions can be accessed using 66 `#define ZSTD_STATIC_LINKING_ONLY` before including zstd.h. 67 68 Advanced experimental APIs should never be used with a dynamically-linked 69 library. They are not "stable"; their definitions or signatures may change in 70 the future. Only static linking is allowed. 71<BR></pre> 72 73<a name="Chapter2"></a><h2>Version</h2><pre></pre> 74 75<pre><b>unsigned ZSTD_versionNumber(void); </b>/**< to check runtime library version */<b> 76</b></pre><BR> 77<a name="Chapter3"></a><h2>Simple API</h2><pre></pre> 78 79<pre><b>size_t ZSTD_compress( void* dst, size_t dstCapacity, 80 const void* src, size_t srcSize, 81 int compressionLevel); 82</b><p> Compresses `src` content as a single zstd compressed frame into already allocated `dst`. 83 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`. 84 @return : compressed size written into `dst` (<= `dstCapacity), 85 or an error code if it fails (which can be tested using ZSTD_isError()). 86</p></pre><BR> 87 88<pre><b>size_t ZSTD_decompress( void* dst, size_t dstCapacity, 89 const void* src, size_t compressedSize); 90</b><p> `compressedSize` : must be the _exact_ size of some number of compressed and/or skippable frames. 91 `dstCapacity` is an upper bound of originalSize to regenerate. 92 If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data. 93 @return : the number of bytes decompressed into `dst` (<= `dstCapacity`), 94 or an errorCode if it fails (which can be tested using ZSTD_isError()). 95</p></pre><BR> 96 97<pre><b>#define ZSTD_CONTENTSIZE_UNKNOWN (0ULL - 1) 98#define ZSTD_CONTENTSIZE_ERROR (0ULL - 2) 99unsigned long long ZSTD_getFrameContentSize(const void *src, size_t srcSize); 100</b><p> `src` should point to the start of a ZSTD encoded frame. 101 `srcSize` must be at least as large as the frame header. 102 hint : any size >= `ZSTD_frameHeaderSize_max` is large enough. 103 @return : - decompressed size of `src` frame content, if known 104 - ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined 105 - ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small) 106 note 1 : a 0 return value means the frame is valid but "empty". 107 note 2 : decompressed size is an optional field, it may not be present, typically in streaming mode. 108 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size. 109 In which case, it's necessary to use streaming mode to decompress data. 110 Optionally, application can rely on some implicit limit, 111 as ZSTD_decompress() only needs an upper bound of decompressed size. 112 (For example, data could be necessarily cut into blocks <= 16 KB). 113 note 3 : decompressed size is always present when compression is completed using single-pass functions, 114 such as ZSTD_compress(), ZSTD_compressCCtx() ZSTD_compress_usingDict() or ZSTD_compress_usingCDict(). 115 note 4 : decompressed size can be very large (64-bits value), 116 potentially larger than what local system can handle as a single memory segment. 117 In which case, it's necessary to use streaming mode to decompress data. 118 note 5 : If source is untrusted, decompressed size could be wrong or intentionally modified. 119 Always ensure return value fits within application's authorized limits. 120 Each application can set its own limits. 121 note 6 : This function replaces ZSTD_getDecompressedSize() 122</p></pre><BR> 123 124<pre><b>unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize); 125</b><p> NOTE: This function is now obsolete, in favor of ZSTD_getFrameContentSize(). 126 Both functions work the same way, but ZSTD_getDecompressedSize() blends 127 "empty", "unknown" and "error" results to the same return value (0), 128 while ZSTD_getFrameContentSize() gives them separate return values. 129 @return : decompressed size of `src` frame content _if known and not empty_, 0 otherwise. 130</p></pre><BR> 131 132<pre><b>size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize); 133</b><p> `src` should point to the start of a ZSTD frame or skippable frame. 134 `srcSize` must be >= first frame size 135 @return : the compressed size of the first frame starting at `src`, 136 suitable to pass as `srcSize` to `ZSTD_decompress` or similar, 137 or an error code if input is invalid 138</p></pre><BR> 139 140<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> 141size_t ZSTD_compressBound(size_t srcSize); </b>/*!< maximum compressed size in worst case single-pass scenario */<b> 142unsigned ZSTD_isError(size_t code); </b>/*!< tells if a `size_t` function result is an error code */<b> 143const char* ZSTD_getErrorName(size_t code); </b>/*!< provides readable string from an error code */<b> 144int ZSTD_minCLevel(void); </b>/*!< minimum negative compression level allowed */<b> 145int ZSTD_maxCLevel(void); </b>/*!< maximum compression level available */<b> 146</pre></b><BR> 147<a name="Chapter4"></a><h2>Explicit context</h2><pre></pre> 148 149<h3>Compression context</h3><pre> When compressing many times, 150 it is recommended to allocate a context just once, 151 and re-use it for each successive compression operation. 152 This will make workload friendlier for system's memory. 153 Note : re-using context is just a speed / resource optimization. 154 It doesn't change the compression ratio, which remains identical. 155 Note 2 : In multi-threaded environments, 156 use one different context per thread for parallel execution. 157 158</pre><b><pre>typedef struct ZSTD_CCtx_s ZSTD_CCtx; 159ZSTD_CCtx* ZSTD_createCCtx(void); 160size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx); 161</pre></b><BR> 162<pre><b>size_t ZSTD_compressCCtx(ZSTD_CCtx* cctx, 163 void* dst, size_t dstCapacity, 164 const void* src, size_t srcSize, 165 int compressionLevel); 166</b><p> Same as ZSTD_compress(), using an explicit ZSTD_CCtx. 167 Important : in order to behave similarly to `ZSTD_compress()`, 168 this function compresses at requested compression level, 169 __ignoring any other parameter__ . 170 If any advanced parameter was set using the advanced API, 171 they will all be reset. Only `compressionLevel` remains. 172 173</p></pre><BR> 174 175<h3>Decompression context</h3><pre> When decompressing many times, 176 it is recommended to allocate a context only once, 177 and re-use it for each successive compression operation. 178 This will make workload friendlier for system's memory. 179 Use one context per thread for parallel execution. 180</pre><b><pre>typedef struct ZSTD_DCtx_s ZSTD_DCtx; 181ZSTD_DCtx* ZSTD_createDCtx(void); 182size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx); 183</pre></b><BR> 184<pre><b>size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx, 185 void* dst, size_t dstCapacity, 186 const void* src, size_t srcSize); 187</b><p> Same as ZSTD_decompress(), 188 requires an allocated ZSTD_DCtx. 189 Compatible with sticky parameters. 190 191</p></pre><BR> 192 193<a name="Chapter5"></a><h2>Advanced compression API</h2><pre></pre> 194 195<pre><b>typedef enum { ZSTD_fast=1, 196 ZSTD_dfast=2, 197 ZSTD_greedy=3, 198 ZSTD_lazy=4, 199 ZSTD_lazy2=5, 200 ZSTD_btlazy2=6, 201 ZSTD_btopt=7, 202 ZSTD_btultra=8, 203 ZSTD_btultra2=9 204 </b>/* note : new strategies _might_ be added in the future.<b> 205 Only the order (from fast to strong) is guaranteed */ 206} ZSTD_strategy; 207</b></pre><BR> 208<pre><b>typedef enum { 209 210 </b>/* compression parameters<b> 211 * Note: When compressing with a ZSTD_CDict these parameters are superseded 212 * by the parameters used to construct the ZSTD_CDict. 213 * See ZSTD_CCtx_refCDict() for more info (superseded-by-cdict). */ 214 ZSTD_c_compressionLevel=100, </b>/* Set compression parameters according to pre-defined cLevel table.<b> 215 * Note that exact compression parameters are dynamically determined, 216 * depending on both compression level and srcSize (when known). 217 * Default level is ZSTD_CLEVEL_DEFAULT==3. 218 * Special: value 0 means default, which is controlled by ZSTD_CLEVEL_DEFAULT. 219 * Note 1 : it's possible to pass a negative compression level. 220 * Note 2 : setting a level does not automatically set all other compression parameters 221 * to default. Setting this will however eventually dynamically impact the compression 222 * parameters which have not been manually set. The manually set 223 * ones will 'stick'. */ 224 </b>/* Advanced compression parameters :<b> 225 * It's possible to pin down compression parameters to some specific values. 226 * In which case, these values are no longer dynamically selected by the compressor */ 227 ZSTD_c_windowLog=101, </b>/* Maximum allowed back-reference distance, expressed as power of 2.<b> 228 * This will set a memory budget for streaming decompression, 229 * with larger values requiring more memory 230 * and typically compressing more. 231 * Must be clamped between ZSTD_WINDOWLOG_MIN and ZSTD_WINDOWLOG_MAX. 232 * Special: value 0 means "use default windowLog". 233 * Note: Using a windowLog greater than ZSTD_WINDOWLOG_LIMIT_DEFAULT 234 * requires explicitly allowing such size at streaming decompression stage. */ 235 ZSTD_c_hashLog=102, </b>/* Size of the initial probe table, as a power of 2.<b> 236 * Resulting memory usage is (1 << (hashLog+2)). 237 * Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX. 238 * Larger tables improve compression ratio of strategies <= dFast, 239 * and improve speed of strategies > dFast. 240 * Special: value 0 means "use default hashLog". */ 241 ZSTD_c_chainLog=103, </b>/* Size of the multi-probe search table, as a power of 2.<b> 242 * Resulting memory usage is (1 << (chainLog+2)). 243 * Must be clamped between ZSTD_CHAINLOG_MIN and ZSTD_CHAINLOG_MAX. 244 * Larger tables result in better and slower compression. 245 * This parameter is useless for "fast" strategy. 246 * It's still useful when using "dfast" strategy, 247 * in which case it defines a secondary probe table. 248 * Special: value 0 means "use default chainLog". */ 249 ZSTD_c_searchLog=104, </b>/* Number of search attempts, as a power of 2.<b> 250 * More attempts result in better and slower compression. 251 * This parameter is useless for "fast" and "dFast" strategies. 252 * Special: value 0 means "use default searchLog". */ 253 ZSTD_c_minMatch=105, </b>/* Minimum size of searched matches.<b> 254 * Note that Zstandard can still find matches of smaller size, 255 * it just tweaks its search algorithm to look for this size and larger. 256 * Larger values increase compression and decompression speed, but decrease ratio. 257 * Must be clamped between ZSTD_MINMATCH_MIN and ZSTD_MINMATCH_MAX. 258 * Note that currently, for all strategies < btopt, effective minimum is 4. 259 * , for all strategies > fast, effective maximum is 6. 260 * Special: value 0 means "use default minMatchLength". */ 261 ZSTD_c_targetLength=106, </b>/* Impact of this field depends on strategy.<b> 262 * For strategies btopt, btultra & btultra2: 263 * Length of Match considered "good enough" to stop search. 264 * Larger values make compression stronger, and slower. 265 * For strategy fast: 266 * Distance between match sampling. 267 * Larger values make compression faster, and weaker. 268 * Special: value 0 means "use default targetLength". */ 269 ZSTD_c_strategy=107, </b>/* See ZSTD_strategy enum definition.<b> 270 * The higher the value of selected strategy, the more complex it is, 271 * resulting in stronger and slower compression. 272 * Special: value 0 means "use default strategy". */ 273 274 </b>/* LDM mode parameters */<b> 275 ZSTD_c_enableLongDistanceMatching=160, </b>/* Enable long distance matching.<b> 276 * This parameter is designed to improve compression ratio 277 * for large inputs, by finding large matches at long distance. 278 * It increases memory usage and window size. 279 * Note: enabling this parameter increases default ZSTD_c_windowLog to 128 MB 280 * except when expressly set to a different value. */ 281 ZSTD_c_ldmHashLog=161, </b>/* Size of the table for long distance matching, as a power of 2.<b> 282 * Larger values increase memory usage and compression ratio, 283 * but decrease compression speed. 284 * Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX 285 * default: windowlog - 7. 286 * Special: value 0 means "automatically determine hashlog". */ 287 ZSTD_c_ldmMinMatch=162, </b>/* Minimum match size for long distance matcher.<b> 288 * Larger/too small values usually decrease compression ratio. 289 * Must be clamped between ZSTD_LDM_MINMATCH_MIN and ZSTD_LDM_MINMATCH_MAX. 290 * Special: value 0 means "use default value" (default: 64). */ 291 ZSTD_c_ldmBucketSizeLog=163, </b>/* Log size of each bucket in the LDM hash table for collision resolution.<b> 292 * Larger values improve collision resolution but decrease compression speed. 293 * The maximum value is ZSTD_LDM_BUCKETSIZELOG_MAX. 294 * Special: value 0 means "use default value" (default: 3). */ 295 ZSTD_c_ldmHashRateLog=164, </b>/* Frequency of inserting/looking up entries into the LDM hash table.<b> 296 * Must be clamped between 0 and (ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN). 297 * Default is MAX(0, (windowLog - ldmHashLog)), optimizing hash table usage. 298 * Larger values improve compression speed. 299 * Deviating far from default value will likely result in a compression ratio decrease. 300 * Special: value 0 means "automatically determine hashRateLog". */ 301 302 </b>/* frame parameters */<b> 303 ZSTD_c_contentSizeFlag=200, </b>/* Content size will be written into frame header _whenever known_ (default:1)<b> 304 * Content size must be known at the beginning of compression. 305 * This is automatically the case when using ZSTD_compress2(), 306 * For streaming scenarios, content size must be provided with ZSTD_CCtx_setPledgedSrcSize() */ 307 ZSTD_c_checksumFlag=201, </b>/* A 32-bits checksum of content is written at end of frame (default:0) */<b> 308 ZSTD_c_dictIDFlag=202, </b>/* When applicable, dictionary's ID is written into frame header (default:1) */<b> 309 310 </b>/* multi-threading parameters */<b> 311 </b>/* These parameters are only useful if multi-threading is enabled (compiled with build macro ZSTD_MULTITHREAD).<b> 312 * They return an error otherwise. */ 313 ZSTD_c_nbWorkers=400, </b>/* Select how many threads will be spawned to compress in parallel.<b> 314 * When nbWorkers >= 1, triggers asynchronous mode when used with ZSTD_compressStream*() : 315 * ZSTD_compressStream*() consumes input and flush output if possible, but immediately gives back control to caller, 316 * while compression work is performed in parallel, within worker threads. 317 * (note : a strong exception to this rule is when first invocation of ZSTD_compressStream2() sets ZSTD_e_end : 318 * in which case, ZSTD_compressStream2() delegates to ZSTD_compress2(), which is always a blocking call). 319 * More workers improve speed, but also increase memory usage. 320 * Default value is `0`, aka "single-threaded mode" : no worker is spawned, compression is performed inside Caller's thread, all invocations are blocking */ 321 ZSTD_c_jobSize=401, </b>/* Size of a compression job. This value is enforced only when nbWorkers >= 1.<b> 322 * Each compression job is completed in parallel, so this value can indirectly impact the nb of active threads. 323 * 0 means default, which is dynamically determined based on compression parameters. 324 * Job size must be a minimum of overlap size, or 1 MB, whichever is largest. 325 * The minimum size is automatically and transparently enforced. */ 326 ZSTD_c_overlapLog=402, </b>/* Control the overlap size, as a fraction of window size.<b> 327 * The overlap size is an amount of data reloaded from previous job at the beginning of a new job. 328 * It helps preserve compression ratio, while each job is compressed in parallel. 329 * This value is enforced only when nbWorkers >= 1. 330 * Larger values increase compression ratio, but decrease speed. 331 * Possible values range from 0 to 9 : 332 * - 0 means "default" : value will be determined by the library, depending on strategy 333 * - 1 means "no overlap" 334 * - 9 means "full overlap", using a full window size. 335 * Each intermediate rank increases/decreases load size by a factor 2 : 336 * 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 337 * default value varies between 6 and 9, depending on strategy */ 338 339 </b>/* note : additional experimental parameters are also available<b> 340 * within the experimental section of the API. 341 * At the time of this writing, they include : 342 * ZSTD_c_rsyncable 343 * ZSTD_c_format 344 * ZSTD_c_forceMaxWindow 345 * ZSTD_c_forceAttachDict 346 * ZSTD_c_literalCompressionMode 347 * ZSTD_c_targetCBlockSize 348 * ZSTD_c_srcSizeHint 349 * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them. 350 * note : never ever use experimentalParam? names directly; 351 * also, the enums values themselves are unstable and can still change. 352 */ 353 ZSTD_c_experimentalParam1=500, 354 ZSTD_c_experimentalParam2=10, 355 ZSTD_c_experimentalParam3=1000, 356 ZSTD_c_experimentalParam4=1001, 357 ZSTD_c_experimentalParam5=1002, 358 ZSTD_c_experimentalParam6=1003, 359 ZSTD_c_experimentalParam7=1004 360} ZSTD_cParameter; 361</b></pre><BR> 362<pre><b>typedef struct { 363 size_t error; 364 int lowerBound; 365 int upperBound; 366} ZSTD_bounds; 367</b></pre><BR> 368<pre><b>ZSTD_bounds ZSTD_cParam_getBounds(ZSTD_cParameter cParam); 369</b><p> All parameters must belong to an interval with lower and upper bounds, 370 otherwise they will either trigger an error or be automatically clamped. 371 @return : a structure, ZSTD_bounds, which contains 372 - an error status field, which must be tested using ZSTD_isError() 373 - lower and upper bounds, both inclusive 374 375</p></pre><BR> 376 377<pre><b>size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int value); 378</b><p> Set one compression parameter, selected by enum ZSTD_cParameter. 379 All parameters have valid bounds. Bounds can be queried using ZSTD_cParam_getBounds(). 380 Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter). 381 Setting a parameter is generally only possible during frame initialization (before starting compression). 382 Exception : when using multi-threading mode (nbWorkers >= 1), 383 the following parameters can be updated _during_ compression (within same frame): 384 => compressionLevel, hashLog, chainLog, searchLog, minMatch, targetLength and strategy. 385 new parameters will be active for next job only (after a flush()). 386 @return : an error code (which can be tested using ZSTD_isError()). 387 388</p></pre><BR> 389 390<pre><b>size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize); 391</b><p> Total input data size to be compressed as a single frame. 392 Value will be written in frame header, unless if explicitly forbidden using ZSTD_c_contentSizeFlag. 393 This value will also be controlled at end of frame, and trigger an error if not respected. 394 @result : 0, or an error code (which can be tested with ZSTD_isError()). 395 Note 1 : pledgedSrcSize==0 actually means zero, aka an empty frame. 396 In order to mean "unknown content size", pass constant ZSTD_CONTENTSIZE_UNKNOWN. 397 ZSTD_CONTENTSIZE_UNKNOWN is default value for any new frame. 398 Note 2 : pledgedSrcSize is only valid once, for the next frame. 399 It's discarded at the end of the frame, and replaced by ZSTD_CONTENTSIZE_UNKNOWN. 400 Note 3 : Whenever all input data is provided and consumed in a single round, 401 for example with ZSTD_compress2(), 402 or invoking immediately ZSTD_compressStream2(,,,ZSTD_e_end), 403 this value is automatically overridden by srcSize instead. 404 405</p></pre><BR> 406 407<pre><b>typedef enum { 408 ZSTD_reset_session_only = 1, 409 ZSTD_reset_parameters = 2, 410 ZSTD_reset_session_and_parameters = 3 411} ZSTD_ResetDirective; 412</b></pre><BR> 413<pre><b>size_t ZSTD_CCtx_reset(ZSTD_CCtx* cctx, ZSTD_ResetDirective reset); 414</b><p> There are 2 different things that can be reset, independently or jointly : 415 - The session : will stop compressing current frame, and make CCtx ready to start a new one. 416 Useful after an error, or to interrupt any ongoing compression. 417 Any internal data not yet flushed is cancelled. 418 Compression parameters and dictionary remain unchanged. 419 They will be used to compress next frame. 420 Resetting session never fails. 421 - The parameters : changes all parameters back to "default". 422 This removes any reference to any dictionary too. 423 Parameters can only be changed between 2 sessions (i.e. no compression is currently ongoing) 424 otherwise the reset fails, and function returns an error value (which can be tested using ZSTD_isError()) 425 - Both : similar to resetting the session, followed by resetting parameters. 426 427</p></pre><BR> 428 429<pre><b>size_t ZSTD_compress2( ZSTD_CCtx* cctx, 430 void* dst, size_t dstCapacity, 431 const void* src, size_t srcSize); 432</b><p> Behave the same as ZSTD_compressCCtx(), but compression parameters are set using the advanced API. 433 ZSTD_compress2() always starts a new frame. 434 Should cctx hold data from a previously unfinished frame, everything about it is forgotten. 435 - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*() 436 - The function is always blocking, returns when compression is completed. 437 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`. 438 @return : compressed size written into `dst` (<= `dstCapacity), 439 or an error code if it fails (which can be tested using ZSTD_isError()). 440 441</p></pre><BR> 442 443<a name="Chapter6"></a><h2>Advanced decompression API</h2><pre></pre> 444 445<pre><b>typedef enum { 446 447 ZSTD_d_windowLogMax=100, </b>/* Select a size limit (in power of 2) beyond which<b> 448 * the streaming API will refuse to allocate memory buffer 449 * in order to protect the host from unreasonable memory requirements. 450 * This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode. 451 * By default, a decompression context accepts window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT). 452 * Special: value 0 means "use default maximum windowLog". */ 453 454 </b>/* note : additional experimental parameters are also available<b> 455 * within the experimental section of the API. 456 * At the time of this writing, they include : 457 * ZSTD_d_format 458 * ZSTD_d_stableOutBuffer 459 * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them. 460 * note : never ever use experimentalParam? names directly 461 */ 462 ZSTD_d_experimentalParam1=1000, 463 ZSTD_d_experimentalParam2=1001 464 465} ZSTD_dParameter; 466</b></pre><BR> 467<pre><b>ZSTD_bounds ZSTD_dParam_getBounds(ZSTD_dParameter dParam); 468</b><p> All parameters must belong to an interval with lower and upper bounds, 469 otherwise they will either trigger an error or be automatically clamped. 470 @return : a structure, ZSTD_bounds, which contains 471 - an error status field, which must be tested using ZSTD_isError() 472 - both lower and upper bounds, inclusive 473 474</p></pre><BR> 475 476<pre><b>size_t ZSTD_DCtx_setParameter(ZSTD_DCtx* dctx, ZSTD_dParameter param, int value); 477</b><p> Set one compression parameter, selected by enum ZSTD_dParameter. 478 All parameters have valid bounds. Bounds can be queried using ZSTD_dParam_getBounds(). 479 Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter). 480 Setting a parameter is only possible during frame initialization (before starting decompression). 481 @return : 0, or an error code (which can be tested using ZSTD_isError()). 482 483</p></pre><BR> 484 485<pre><b>size_t ZSTD_DCtx_reset(ZSTD_DCtx* dctx, ZSTD_ResetDirective reset); 486</b><p> Return a DCtx to clean state. 487 Session and parameters can be reset jointly or separately. 488 Parameters can only be reset when no active frame is being decompressed. 489 @return : 0, or an error code, which can be tested with ZSTD_isError() 490 491</p></pre><BR> 492 493<a name="Chapter7"></a><h2>Streaming</h2><pre></pre> 494 495<pre><b>typedef struct ZSTD_inBuffer_s { 496 const void* src; </b>/**< start of input buffer */<b> 497 size_t size; </b>/**< size of input buffer */<b> 498 size_t pos; </b>/**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */<b> 499} ZSTD_inBuffer; 500</b></pre><BR> 501<pre><b>typedef struct ZSTD_outBuffer_s { 502 void* dst; </b>/**< start of output buffer */<b> 503 size_t size; </b>/**< size of output buffer */<b> 504 size_t pos; </b>/**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */<b> 505} ZSTD_outBuffer; 506</b></pre><BR> 507<a name="Chapter8"></a><h2>Streaming compression - HowTo</h2><pre> 508 A ZSTD_CStream object is required to track streaming operation. 509 Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources. 510 ZSTD_CStream objects can be reused multiple times on consecutive compression operations. 511 It is recommended to re-use ZSTD_CStream since it will play nicer with system's memory, by re-using already allocated memory. 512 513 For parallel execution, use one separate ZSTD_CStream per thread. 514 515 note : since v1.3.0, ZSTD_CStream and ZSTD_CCtx are the same thing. 516 517 Parameters are sticky : when starting a new compression on the same context, 518 it will re-use the same sticky parameters as previous compression session. 519 When in doubt, it's recommended to fully initialize the context before usage. 520 Use ZSTD_CCtx_reset() to reset the context and ZSTD_CCtx_setParameter(), 521 ZSTD_CCtx_setPledgedSrcSize(), or ZSTD_CCtx_loadDictionary() and friends to 522 set more specific parameters, the pledged source size, or load a dictionary. 523 524 Use ZSTD_compressStream2() with ZSTD_e_continue as many times as necessary to 525 consume input stream. The function will automatically update both `pos` 526 fields within `input` and `output`. 527 Note that the function may not consume the entire input, for example, because 528 the output buffer is already full, in which case `input.pos < input.size`. 529 The caller must check if input has been entirely consumed. 530 If not, the caller must make some room to receive more compressed data, 531 and then present again remaining input data. 532 note: ZSTD_e_continue is guaranteed to make some forward progress when called, 533 but doesn't guarantee maximal forward progress. This is especially relevant 534 when compressing with multiple threads. The call won't block if it can 535 consume some input, but if it can't it will wait for some, but not all, 536 output to be flushed. 537 @return : provides a minimum amount of data remaining to be flushed from internal buffers 538 or an error code, which can be tested using ZSTD_isError(). 539 540 At any moment, it's possible to flush whatever data might remain stuck within internal buffer, 541 using ZSTD_compressStream2() with ZSTD_e_flush. `output->pos` will be updated. 542 Note that, if `output->size` is too small, a single invocation with ZSTD_e_flush might not be enough (return code > 0). 543 In which case, make some room to receive more compressed data, and call again ZSTD_compressStream2() with ZSTD_e_flush. 544 You must continue calling ZSTD_compressStream2() with ZSTD_e_flush until it returns 0, at which point you can change the 545 operation. 546 note: ZSTD_e_flush will flush as much output as possible, meaning when compressing with multiple threads, it will 547 block until the flush is complete or the output buffer is full. 548 @return : 0 if internal buffers are entirely flushed, 549 >0 if some data still present within internal buffer (the value is minimal estimation of remaining size), 550 or an error code, which can be tested using ZSTD_isError(). 551 552 Calling ZSTD_compressStream2() with ZSTD_e_end instructs to finish a frame. 553 It will perform a flush and write frame epilogue. 554 The epilogue is required for decoders to consider a frame completed. 555 flush operation is the same, and follows same rules as calling ZSTD_compressStream2() with ZSTD_e_flush. 556 You must continue calling ZSTD_compressStream2() with ZSTD_e_end until it returns 0, at which point you are free to 557 start a new frame. 558 note: ZSTD_e_end will flush as much output as possible, meaning when compressing with multiple threads, it will 559 block until the flush is complete or the output buffer is full. 560 @return : 0 if frame fully completed and fully flushed, 561 >0 if some data still present within internal buffer (the value is minimal estimation of remaining size), 562 or an error code, which can be tested using ZSTD_isError(). 563 564 565<BR></pre> 566 567<pre><b>typedef ZSTD_CCtx ZSTD_CStream; </b>/**< CCtx and CStream are now effectively same object (>= v1.3.0) */<b> 568</b></pre><BR> 569<h3>ZSTD_CStream management functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream(void); 570size_t ZSTD_freeCStream(ZSTD_CStream* zcs); 571</pre></b><BR> 572<h3>Streaming compression functions</h3><pre></pre><b><pre>typedef enum { 573 ZSTD_e_continue=0, </b>/* collect more data, encoder decides when to output compressed result, for optimal compression ratio */<b> 574 ZSTD_e_flush=1, </b>/* flush any data provided so far,<b> 575 * it creates (at least) one new block, that can be decoded immediately on reception; 576 * frame will continue: any future data can still reference previously compressed data, improving compression. 577 * note : multithreaded compression will block to flush as much output as possible. */ 578 ZSTD_e_end=2 </b>/* flush any remaining data _and_ close current frame.<b> 579 * note that frame is only closed after compressed data is fully flushed (return value == 0). 580 * After that point, any additional data starts a new frame. 581 * note : each frame is independent (does not reference any content from previous frame). 582 : note : multithreaded compression will block to flush as much output as possible. */ 583} ZSTD_EndDirective; 584</pre></b><BR> 585<pre><b>size_t ZSTD_compressStream2( ZSTD_CCtx* cctx, 586 ZSTD_outBuffer* output, 587 ZSTD_inBuffer* input, 588 ZSTD_EndDirective endOp); 589</b><p> Behaves about the same as ZSTD_compressStream, with additional control on end directive. 590 - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*() 591 - Compression parameters cannot be changed once compression is started (save a list of exceptions in multi-threading mode) 592 - output->pos must be <= dstCapacity, input->pos must be <= srcSize 593 - output->pos and input->pos will be updated. They are guaranteed to remain below their respective limit. 594 - When nbWorkers==0 (default), function is blocking : it completes its job before returning to caller. 595 - 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, 596 and then immediately returns, just indicating that there is some data remaining to be flushed. 597 The function nonetheless guarantees forward progress : it will return only after it reads or write at least 1+ byte. 598 - 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. 599 - @return provides a minimum amount of data remaining to be flushed from internal buffers 600 or an error code, which can be tested using ZSTD_isError(). 601 if @return != 0, flush is not fully completed, there is still some data left within internal buffers. 602 This is useful for ZSTD_e_flush, since in this case more flushes are necessary to empty all buffers. 603 For ZSTD_e_end, @return == 0 when internal buffers are fully flushed and frame is completed. 604 - after a ZSTD_e_end directive, if internal buffer is not fully flushed (@return != 0), 605 only ZSTD_e_end or ZSTD_e_flush operations are allowed. 606 Before starting a new compression job, or changing compression parameters, 607 it is required to fully flush internal buffers. 608 609</p></pre><BR> 610 611<pre><b>size_t ZSTD_CStreamInSize(void); </b>/**< recommended size for input buffer */<b> 612</b></pre><BR> 613<pre><b>size_t ZSTD_CStreamOutSize(void); </b>/**< recommended size for output buffer. Guarantee to successfully flush at least one complete compressed block. */<b> 614</b></pre><BR> 615<pre><b>size_t ZSTD_initCStream(ZSTD_CStream* zcs, int compressionLevel); 616</b>/*!<b> 617 * Alternative for ZSTD_compressStream2(zcs, output, input, ZSTD_e_continue). 618 * NOTE: The return value is different. ZSTD_compressStream() returns a hint for 619 * the next read size (if non-zero and not an error). ZSTD_compressStream2() 620 * returns the minimum nb of bytes left to flush (if non-zero and not an error). 621 */ 622size_t ZSTD_compressStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output, ZSTD_inBuffer* input); 623</b>/*! Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_flush). */<b> 624size_t ZSTD_flushStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output); 625</b>/*! Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_end). */<b> 626size_t ZSTD_endStream(ZSTD_CStream* zcs, ZSTD_outBuffer* output); 627</b><p> 628 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 629 ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any) 630 ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel); 631 632</p></pre><BR> 633 634<a name="Chapter9"></a><h2>Streaming decompression - HowTo</h2><pre> 635 A ZSTD_DStream object is required to track streaming operations. 636 Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources. 637 ZSTD_DStream objects can be re-used multiple times. 638 639 Use ZSTD_initDStream() to start a new decompression operation. 640 @return : recommended first input size 641 Alternatively, use advanced API to set specific properties. 642 643 Use ZSTD_decompressStream() repetitively to consume your input. 644 The function will update both `pos` fields. 645 If `input.pos < input.size`, some input has not been consumed. 646 It's up to the caller to present again remaining data. 647 The function tries to flush all data decoded immediately, respecting output buffer size. 648 If `output.pos < output.size`, decoder has flushed everything it could. 649 But if `output.pos == output.size`, there might be some data left within internal buffers., 650 In which case, call ZSTD_decompressStream() again to flush whatever remains in the buffer. 651 Note : with no additional input provided, amount of data flushed is necessarily <= ZSTD_BLOCKSIZE_MAX. 652 @return : 0 when a frame is completely decoded and fully flushed, 653 or an error code, which can be tested using ZSTD_isError(), 654 or any other value > 0, which means there is still some decoding or flushing to do to complete current frame : 655 the return value is a suggested next input size (just a hint for better latency) 656 that will never request more than the remaining frame size. 657 658<BR></pre> 659 660<pre><b>typedef ZSTD_DCtx ZSTD_DStream; </b>/**< DCtx and DStream are now effectively same object (>= v1.3.0) */<b> 661</b></pre><BR> 662<h3>ZSTD_DStream management functions</h3><pre></pre><b><pre>ZSTD_DStream* ZSTD_createDStream(void); 663size_t ZSTD_freeDStream(ZSTD_DStream* zds); 664</pre></b><BR> 665<h3>Streaming decompression functions</h3><pre></pre><b><pre></pre></b><BR> 666<pre><b>size_t ZSTD_DStreamInSize(void); </b>/*!< recommended size for input buffer */<b> 667</b></pre><BR> 668<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> 669</b></pre><BR> 670<a name="Chapter10"></a><h2>Simple dictionary API</h2><pre></pre> 671 672<pre><b>size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx, 673 void* dst, size_t dstCapacity, 674 const void* src, size_t srcSize, 675 const void* dict,size_t dictSize, 676 int compressionLevel); 677</b><p> Compression at an explicit compression level using a Dictionary. 678 A dictionary can be any arbitrary data segment (also called a prefix), 679 or a buffer with specified information (see dictBuilder/zdict.h). 680 Note : This function loads the dictionary, resulting in significant startup delay. 681 It's intended for a dictionary used only once. 682 Note 2 : When `dict == NULL || dictSize < 8` no dictionary is used. 683</p></pre><BR> 684 685<pre><b>size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx, 686 void* dst, size_t dstCapacity, 687 const void* src, size_t srcSize, 688 const void* dict,size_t dictSize); 689</b><p> Decompression using a known Dictionary. 690 Dictionary must be identical to the one used during compression. 691 Note : This function loads the dictionary, resulting in significant startup delay. 692 It's intended for a dictionary used only once. 693 Note : When `dict == NULL || dictSize < 8` no dictionary is used. 694</p></pre><BR> 695 696<a name="Chapter11"></a><h2>Bulk processing dictionary API</h2><pre></pre> 697 698<pre><b>ZSTD_CDict* ZSTD_createCDict(const void* dictBuffer, size_t dictSize, 699 int compressionLevel); 700</b><p> When compressing multiple messages or blocks using the same dictionary, 701 it's recommended to digest the dictionary only once, since it's a costly operation. 702 ZSTD_createCDict() will create a state from digesting a dictionary. 703 The resulting state can be used for future compression operations with very limited startup cost. 704 ZSTD_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only. 705 @dictBuffer can be released after ZSTD_CDict creation, because its content is copied within CDict. 706 Note 1 : Consider experimental function `ZSTD_createCDict_byReference()` if you prefer to not duplicate @dictBuffer content. 707 Note 2 : A ZSTD_CDict can be created from an empty @dictBuffer, 708 in which case the only thing that it transports is the @compressionLevel. 709 This can be useful in a pipeline featuring ZSTD_compress_usingCDict() exclusively, 710 expecting a ZSTD_CDict parameter with any data, including those without a known dictionary. 711</p></pre><BR> 712 713<pre><b>size_t ZSTD_freeCDict(ZSTD_CDict* CDict); 714</b><p> Function frees memory allocated by ZSTD_createCDict(). 715</p></pre><BR> 716 717<pre><b>size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx, 718 void* dst, size_t dstCapacity, 719 const void* src, size_t srcSize, 720 const ZSTD_CDict* cdict); 721</b><p> Compression using a digested Dictionary. 722 Recommended when same dictionary is used multiple times. 723 Note : compression level is _decided at dictionary creation time_, 724 and frame parameters are hardcoded (dictID=yes, contentSize=yes, checksum=no) 725</p></pre><BR> 726 727<pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dictBuffer, size_t dictSize); 728</b><p> Create a digested dictionary, ready to start decompression operation without startup delay. 729 dictBuffer can be released after DDict creation, as its content is copied inside DDict. 730</p></pre><BR> 731 732<pre><b>size_t ZSTD_freeDDict(ZSTD_DDict* ddict); 733</b><p> Function frees memory allocated with ZSTD_createDDict() 734</p></pre><BR> 735 736<pre><b>size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx, 737 void* dst, size_t dstCapacity, 738 const void* src, size_t srcSize, 739 const ZSTD_DDict* ddict); 740</b><p> Decompression using a digested Dictionary. 741 Recommended when same dictionary is used multiple times. 742</p></pre><BR> 743 744<a name="Chapter12"></a><h2>Dictionary helper functions</h2><pre></pre> 745 746<pre><b>unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize); 747</b><p> Provides the dictID stored within dictionary. 748 if @return == 0, the dictionary is not conformant with Zstandard specification. 749 It can still be loaded, but as a content-only dictionary. 750</p></pre><BR> 751 752<pre><b>unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict); 753</b><p> Provides the dictID of the dictionary loaded into `ddict`. 754 If @return == 0, the dictionary is not conformant to Zstandard specification, or empty. 755 Non-conformant dictionaries can still be loaded, but as content-only dictionaries. 756</p></pre><BR> 757 758<pre><b>unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize); 759</b><p> Provides the dictID required to decompressed the frame stored within `src`. 760 If @return == 0, the dictID could not be decoded. 761 This could for one of the following reasons : 762 - The frame does not require a dictionary to be decoded (most common case). 763 - The frame was built with dictID intentionally removed. Whatever dictionary is necessary is a hidden information. 764 Note : this use case also happens when using a non-conformant dictionary. 765 - `srcSize` is too small, and as a result, the frame header could not be decoded (only possible if `srcSize < ZSTD_FRAMEHEADERSIZE_MAX`). 766 - This is not a Zstandard frame. 767 When identifying the exact failure cause, it's possible to use ZSTD_getFrameHeader(), which will provide a more precise error code. 768</p></pre><BR> 769 770<a name="Chapter13"></a><h2>Advanced dictionary and prefix API</h2><pre> 771 This API allows dictionaries to be used with ZSTD_compress2(), 772 ZSTD_compressStream2(), and ZSTD_decompress(). Dictionaries are sticky, and 773 only reset with the context is reset with ZSTD_reset_parameters or 774 ZSTD_reset_session_and_parameters. Prefixes are single-use. 775<BR></pre> 776 777<pre><b>size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize); 778</b><p> Create an internal CDict from `dict` buffer. 779 Decompression will have to use same dictionary. 780 @result : 0, or an error code (which can be tested with ZSTD_isError()). 781 Special: Loading a NULL (or 0-size) dictionary invalidates previous dictionary, 782 meaning "return to no-dictionary mode". 783 Note 1 : Dictionary is sticky, it will be used for all future compressed frames. 784 To return to "no-dictionary" situation, load a NULL dictionary (or reset parameters). 785 Note 2 : Loading a dictionary involves building tables. 786 It's also a CPU consuming operation, with non-negligible impact on latency. 787 Tables are dependent on compression parameters, and for this reason, 788 compression parameters can no longer be changed after loading a dictionary. 789 Note 3 :`dict` content will be copied internally. 790 Use experimental ZSTD_CCtx_loadDictionary_byReference() to reference content instead. 791 In such a case, dictionary buffer must outlive its users. 792 Note 4 : Use ZSTD_CCtx_loadDictionary_advanced() 793 to precisely select how dictionary content must be interpreted. 794</p></pre><BR> 795 796<pre><b>size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); 797</b><p> Reference a prepared dictionary, to be used for all next compressed frames. 798 Note that compression parameters are enforced from within CDict, 799 and supersede any compression parameter previously set within CCtx. 800 The parameters ignored are labled as "superseded-by-cdict" in the ZSTD_cParameter enum docs. 801 The ignored parameters will be used again if the CCtx is returned to no-dictionary mode. 802 The dictionary will remain valid for future compressed frames using same CCtx. 803 @result : 0, or an error code (which can be tested with ZSTD_isError()). 804 Special : Referencing a NULL CDict means "return to no-dictionary mode". 805 Note 1 : Currently, only one dictionary can be managed. 806 Referencing a new dictionary effectively "discards" any previous one. 807 Note 2 : CDict is just referenced, its lifetime must outlive its usage within CCtx. 808</p></pre><BR> 809 810<pre><b>size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx, 811 const void* prefix, size_t prefixSize); 812</b><p> Reference a prefix (single-usage dictionary) for next compressed frame. 813 A prefix is **only used once**. Tables are discarded at end of frame (ZSTD_e_end). 814 Decompression will need same prefix to properly regenerate data. 815 Compressing with a prefix is similar in outcome as performing a diff and compressing it, 816 but performs much faster, especially during decompression (compression speed is tunable with compression level). 817 @result : 0, or an error code (which can be tested with ZSTD_isError()). 818 Special: Adding any prefix (including NULL) invalidates any previous prefix or dictionary 819 Note 1 : Prefix buffer is referenced. It **must** outlive compression. 820 Its content must remain unmodified during compression. 821 Note 2 : If the intention is to diff some large src data blob with some prior version of itself, 822 ensure that the window size is large enough to contain the entire source. 823 See ZSTD_c_windowLog. 824 Note 3 : Referencing a prefix involves building tables, which are dependent on compression parameters. 825 It's a CPU consuming operation, with non-negligible impact on latency. 826 If there is a need to use the same prefix multiple times, consider loadDictionary instead. 827 Note 4 : By default, the prefix is interpreted as raw content (ZSTD_dct_rawContent). 828 Use experimental ZSTD_CCtx_refPrefix_advanced() to alter dictionary interpretation. 829</p></pre><BR> 830 831<pre><b>size_t ZSTD_DCtx_loadDictionary(ZSTD_DCtx* dctx, const void* dict, size_t dictSize); 832</b><p> Create an internal DDict from dict buffer, 833 to be used to decompress next frames. 834 The dictionary remains valid for all future frames, until explicitly invalidated. 835 @result : 0, or an error code (which can be tested with ZSTD_isError()). 836 Special : Adding a NULL (or 0-size) dictionary invalidates any previous dictionary, 837 meaning "return to no-dictionary mode". 838 Note 1 : Loading a dictionary involves building tables, 839 which has a non-negligible impact on CPU usage and latency. 840 It's recommended to "load once, use many times", to amortize the cost 841 Note 2 :`dict` content will be copied internally, so `dict` can be released after loading. 842 Use ZSTD_DCtx_loadDictionary_byReference() to reference dictionary content instead. 843 Note 3 : Use ZSTD_DCtx_loadDictionary_advanced() to take control of 844 how dictionary content is loaded and interpreted. 845 846</p></pre><BR> 847 848<pre><b>size_t ZSTD_DCtx_refDDict(ZSTD_DCtx* dctx, const ZSTD_DDict* ddict); 849</b><p> Reference a prepared dictionary, to be used to decompress next frames. 850 The dictionary remains active for decompression of future frames using same DCtx. 851 @result : 0, or an error code (which can be tested with ZSTD_isError()). 852 Note 1 : Currently, only one dictionary can be managed. 853 Referencing a new dictionary effectively "discards" any previous one. 854 Special: referencing a NULL DDict means "return to no-dictionary mode". 855 Note 2 : DDict is just referenced, its lifetime must outlive its usage from DCtx. 856 857</p></pre><BR> 858 859<pre><b>size_t ZSTD_DCtx_refPrefix(ZSTD_DCtx* dctx, 860 const void* prefix, size_t prefixSize); 861</b><p> Reference a prefix (single-usage dictionary) to decompress next frame. 862 This is the reverse operation of ZSTD_CCtx_refPrefix(), 863 and must use the same prefix as the one used during compression. 864 Prefix is **only used once**. Reference is discarded at end of frame. 865 End of frame is reached when ZSTD_decompressStream() returns 0. 866 @result : 0, or an error code (which can be tested with ZSTD_isError()). 867 Note 1 : Adding any prefix (including NULL) invalidates any previously set prefix or dictionary 868 Note 2 : Prefix buffer is referenced. It **must** outlive decompression. 869 Prefix buffer must remain unmodified up to the end of frame, 870 reached when ZSTD_decompressStream() returns 0. 871 Note 3 : By default, the prefix is treated as raw content (ZSTD_dct_rawContent). 872 Use ZSTD_CCtx_refPrefix_advanced() to alter dictMode (Experimental section) 873 Note 4 : Referencing a raw content prefix has almost no cpu nor memory cost. 874 A full dictionary is more costly, as it requires building tables. 875 876</p></pre><BR> 877 878<pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx); 879size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx); 880size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs); 881size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds); 882size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict); 883size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict); 884</b><p> These functions give the _current_ memory usage of selected object. 885 Note that object memory usage can evolve (increase or decrease) over time. 886</p></pre><BR> 887 888<a name="Chapter14"></a><h2>experimental API (static linking only)</h2><pre> 889 The following symbols and constants 890 are not planned to join "stable API" status in the near future. 891 They can still change in future versions. 892 Some of them are planned to remain in the static_only section indefinitely. 893 Some of them might be removed in the future (especially when redundant with existing stable functions) 894 895<BR></pre> 896 897<pre><b>typedef struct { 898 unsigned int matchPos; </b>/* Match pos in dst */<b> 899 </b>/* If seqDef.offset > 3, then this is seqDef.offset - 3<b> 900 * If seqDef.offset < 3, then this is the corresponding repeat offset 901 * But if seqDef.offset < 3 and litLength == 0, this is the 902 * repeat offset before the corresponding repeat offset 903 * And if seqDef.offset == 3 and litLength == 0, this is the 904 * most recent repeat offset - 1 905 */ 906 unsigned int offset; 907 unsigned int litLength; </b>/* Literal length */<b> 908 unsigned int matchLength; </b>/* Match length */<b> 909 </b>/* 0 when seq not rep and seqDef.offset otherwise<b> 910 * when litLength == 0 this will be <= 4, otherwise <= 3 like normal 911 */ 912 unsigned int rep; 913} ZSTD_Sequence; 914</b></pre><BR> 915<pre><b>typedef struct { 916 unsigned windowLog; </b>/**< largest match distance : larger == more compression, more memory needed during decompression */<b> 917 unsigned chainLog; </b>/**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */<b> 918 unsigned hashLog; </b>/**< dispatch table : larger == faster, more memory */<b> 919 unsigned searchLog; </b>/**< nb of searches : larger == more compression, slower */<b> 920 unsigned minMatch; </b>/**< match length searched : larger == faster decompression, sometimes less compression */<b> 921 unsigned targetLength; </b>/**< acceptable match size for optimal parser (only) : larger == more compression, slower */<b> 922 ZSTD_strategy strategy; </b>/**< see ZSTD_strategy definition above */<b> 923} ZSTD_compressionParameters; 924</b></pre><BR> 925<pre><b>typedef struct { 926 int contentSizeFlag; </b>/**< 1: content size will be in frame header (when known) */<b> 927 int checksumFlag; </b>/**< 1: generate a 32-bits checksum using XXH64 algorithm at end of frame, for error detection */<b> 928 int noDictIDFlag; </b>/**< 1: no dictID will be saved into frame header (dictID is only useful for dictionary compression) */<b> 929} ZSTD_frameParameters; 930</b></pre><BR> 931<pre><b>typedef struct { 932 ZSTD_compressionParameters cParams; 933 ZSTD_frameParameters fParams; 934} ZSTD_parameters; 935</b></pre><BR> 936<pre><b>typedef enum { 937 ZSTD_dct_auto = 0, </b>/* dictionary is "full" when starting with ZSTD_MAGIC_DICTIONARY, otherwise it is "rawContent" */<b> 938 ZSTD_dct_rawContent = 1, </b>/* ensures dictionary is always loaded as rawContent, even if it starts with ZSTD_MAGIC_DICTIONARY */<b> 939 ZSTD_dct_fullDict = 2 </b>/* refuses to load a dictionary if it does not respect Zstandard's specification, starting with ZSTD_MAGIC_DICTIONARY */<b> 940} ZSTD_dictContentType_e; 941</b></pre><BR> 942<pre><b>typedef enum { 943 ZSTD_dlm_byCopy = 0, </b>/**< Copy dictionary content internally */<b> 944 ZSTD_dlm_byRef = 1 </b>/**< Reference dictionary content -- the dictionary buffer must outlive its users. */<b> 945} ZSTD_dictLoadMethod_e; 946</b></pre><BR> 947<pre><b>typedef enum { 948 ZSTD_f_zstd1 = 0, </b>/* zstd frame format, specified in zstd_compression_format.md (default) */<b> 949 ZSTD_f_zstd1_magicless = 1 </b>/* Variant of zstd frame format, without initial 4-bytes magic number.<b> 950 * Useful to save 4 bytes per generated frame. 951 * Decoder cannot recognise automatically this format, requiring this instruction. */ 952} ZSTD_format_e; 953</b></pre><BR> 954<pre><b>typedef enum { 955 </b>/* Note: this enum and the behavior it controls are effectively internal<b> 956 * implementation details of the compressor. They are expected to continue 957 * to evolve and should be considered only in the context of extremely 958 * advanced performance tuning. 959 * 960 * Zstd currently supports the use of a CDict in three ways: 961 * 962 * - The contents of the CDict can be copied into the working context. This 963 * means that the compression can search both the dictionary and input 964 * while operating on a single set of internal tables. This makes 965 * the compression faster per-byte of input. However, the initial copy of 966 * the CDict's tables incurs a fixed cost at the beginning of the 967 * compression. For small compressions (< 8 KB), that copy can dominate 968 * the cost of the compression. 969 * 970 * - The CDict's tables can be used in-place. In this model, compression is 971 * slower per input byte, because the compressor has to search two sets of 972 * tables. However, this model incurs no start-up cost (as long as the 973 * working context's tables can be reused). For small inputs, this can be 974 * faster than copying the CDict's tables. 975 * 976 * - The CDict's tables are not used at all, and instead we use the working 977 * context alone to reload the dictionary and use params based on the source 978 * size. See ZSTD_compress_insertDictionary() and ZSTD_compress_usingDict(). 979 * This method is effective when the dictionary sizes are very small relative 980 * to the input size, and the input size is fairly large to begin with. 981 * 982 * Zstd has a simple internal heuristic that selects which strategy to use 983 * at the beginning of a compression. However, if experimentation shows that 984 * Zstd is making poor choices, it is possible to override that choice with 985 * this enum. 986 */ 987 ZSTD_dictDefaultAttach = 0, </b>/* Use the default heuristic. */<b> 988 ZSTD_dictForceAttach = 1, </b>/* Never copy the dictionary. */<b> 989 ZSTD_dictForceCopy = 2, </b>/* Always copy the dictionary. */<b> 990 ZSTD_dictForceLoad = 3 </b>/* Always reload the dictionary */<b> 991} ZSTD_dictAttachPref_e; 992</b></pre><BR> 993<pre><b>typedef enum { 994 ZSTD_lcm_auto = 0, </b>/**< Automatically determine the compression mode based on the compression level.<b> 995 * Negative compression levels will be uncompressed, and positive compression 996 * levels will be compressed. */ 997 ZSTD_lcm_huffman = 1, </b>/**< Always attempt Huffman compression. Uncompressed literals will still be<b> 998 * emitted if Huffman compression is not profitable. */ 999 ZSTD_lcm_uncompressed = 2 </b>/**< Always emit uncompressed literals. */<b> 1000} ZSTD_literalCompressionMode_e; 1001</b></pre><BR> 1002<a name="Chapter15"></a><h2>Frame size functions</h2><pre></pre> 1003 1004<pre><b>unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize); 1005</b><p> `src` should point to the start of a series of ZSTD encoded and/or skippable frames 1006 `srcSize` must be the _exact_ size of this series 1007 (i.e. there should be a frame boundary at `src + srcSize`) 1008 @return : - decompressed size of all data in all successive frames 1009 - if the decompressed size cannot be determined: ZSTD_CONTENTSIZE_UNKNOWN 1010 - if an error occurred: ZSTD_CONTENTSIZE_ERROR 1011 1012 note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode. 1013 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size. 1014 In which case, it's necessary to use streaming mode to decompress data. 1015 note 2 : decompressed size is always present when compression is done with ZSTD_compress() 1016 note 3 : decompressed size can be very large (64-bits value), 1017 potentially larger than what local system can handle as a single memory segment. 1018 In which case, it's necessary to use streaming mode to decompress data. 1019 note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified. 1020 Always ensure result fits within application's authorized limits. 1021 Each application can set its own limits. 1022 note 5 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to 1023 read each contained frame header. This is fast as most of the data is skipped, 1024 however it does mean that all frame data must be present and valid. 1025</p></pre><BR> 1026 1027<pre><b>unsigned long long ZSTD_decompressBound(const void* src, size_t srcSize); 1028</b><p> `src` should point to the start of a series of ZSTD encoded and/or skippable frames 1029 `srcSize` must be the _exact_ size of this series 1030 (i.e. there should be a frame boundary at `src + srcSize`) 1031 @return : - upper-bound for the decompressed size of all data in all successive frames 1032 - if an error occured: ZSTD_CONTENTSIZE_ERROR 1033 1034 note 1 : an error can occur if `src` contains an invalid or incorrectly formatted frame. 1035 note 2 : the upper-bound is exact when the decompressed size field is available in every ZSTD encoded frame of `src`. 1036 in this case, `ZSTD_findDecompressedSize` and `ZSTD_decompressBound` return the same value. 1037 note 3 : when the decompressed size field isn't available, the upper-bound for that frame is calculated by: 1038 upper-bound = # blocks * min(128 KB, Window_Size) 1039 1040</p></pre><BR> 1041 1042<pre><b>size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize); 1043</b><p> srcSize must be >= ZSTD_FRAMEHEADERSIZE_PREFIX. 1044 @return : size of the Frame Header, 1045 or an error code (if srcSize is too small) 1046</p></pre><BR> 1047 1048<pre><b>size_t ZSTD_getSequences(ZSTD_CCtx* zc, ZSTD_Sequence* outSeqs, 1049 size_t outSeqsSize, const void* src, size_t srcSize); 1050</b><p> Extract sequences from the sequence store 1051 zc can be used to insert custom compression params. 1052 This function invokes ZSTD_compress2 1053 @return : number of sequences extracted 1054 1055</p></pre><BR> 1056 1057<a name="Chapter16"></a><h2>Memory management</h2><pre></pre> 1058 1059<pre><b>size_t ZSTD_estimateCCtxSize(int compressionLevel); 1060size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams); 1061size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params); 1062size_t ZSTD_estimateDCtxSize(void); 1063</b><p> These functions make it possible to estimate memory usage 1064 of a future {D,C}Ctx, before its creation. 1065 1066 ZSTD_estimateCCtxSize() will provide a memory budget large enough 1067 for any compression level up to selected one. 1068 Note : Unlike ZSTD_estimateCStreamSize*(), this estimate 1069 does not include space for a window buffer. 1070 Therefore, the estimation is only guaranteed for single-shot compressions, not streaming. 1071 The estimate will assume the input may be arbitrarily large, 1072 which is the worst case. 1073 1074 When srcSize can be bound by a known and rather "small" value, 1075 this fact can be used to provide a tighter estimation 1076 because the CCtx compression context will need less memory. 1077 This tighter estimation can be provided by more advanced functions 1078 ZSTD_estimateCCtxSize_usingCParams(), which can be used in tandem with ZSTD_getCParams(), 1079 and ZSTD_estimateCCtxSize_usingCCtxParams(), which can be used in tandem with ZSTD_CCtxParams_setParameter(). 1080 Both can be used to estimate memory using custom compression parameters and arbitrary srcSize limits. 1081 1082 Note 2 : only single-threaded compression is supported. 1083 ZSTD_estimateCCtxSize_usingCCtxParams() will return an error code if ZSTD_c_nbWorkers is >= 1. 1084 1085</p></pre><BR> 1086 1087<pre><b>size_t ZSTD_estimateCStreamSize(int compressionLevel); 1088size_t ZSTD_estimateCStreamSize_usingCParams(ZSTD_compressionParameters cParams); 1089size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params); 1090size_t ZSTD_estimateDStreamSize(size_t windowSize); 1091size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize); 1092</b><p> ZSTD_estimateCStreamSize() will provide a budget large enough for any compression level up to selected one. 1093 It will also consider src size to be arbitrarily "large", which is worst case. 1094 If srcSize is known to always be small, ZSTD_estimateCStreamSize_usingCParams() can provide a tighter estimation. 1095 ZSTD_estimateCStreamSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel. 1096 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. 1097 Note : CStream size estimation is only correct for single-threaded compression. 1098 ZSTD_DStream memory budget depends on window Size. 1099 This information can be passed manually, using ZSTD_estimateDStreamSize, 1100 or deducted from a valid frame Header, using ZSTD_estimateDStreamSize_fromFrame(); 1101 Note : if streaming is init with function ZSTD_init?Stream_usingDict(), 1102 an internal ?Dict will be created, which additional size is not estimated here. 1103 In this case, get total size by adding ZSTD_estimate?DictSize 1104</p></pre><BR> 1105 1106<pre><b>size_t ZSTD_estimateCDictSize(size_t dictSize, int compressionLevel); 1107size_t ZSTD_estimateCDictSize_advanced(size_t dictSize, ZSTD_compressionParameters cParams, ZSTD_dictLoadMethod_e dictLoadMethod); 1108size_t ZSTD_estimateDDictSize(size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod); 1109</b><p> ZSTD_estimateCDictSize() will bet that src size is relatively "small", and content is copied, like ZSTD_createCDict(). 1110 ZSTD_estimateCDictSize_advanced() makes it possible to control compression parameters precisely, like ZSTD_createCDict_advanced(). 1111 Note : dictionaries created by reference (`ZSTD_dlm_byRef`) are logically smaller. 1112 1113</p></pre><BR> 1114 1115<pre><b>ZSTD_CCtx* ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize); 1116ZSTD_CStream* ZSTD_initStaticCStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticCCtx() */<b> 1117</b><p> Initialize an object using a pre-allocated fixed-size buffer. 1118 workspace: The memory area to emplace the object into. 1119 Provided pointer *must be 8-bytes aligned*. 1120 Buffer must outlive object. 1121 workspaceSize: Use ZSTD_estimate*Size() to determine 1122 how large workspace must be to support target scenario. 1123 @return : pointer to object (same address as workspace, just different type), 1124 or NULL if error (size too small, incorrect alignment, etc.) 1125 Note : zstd will never resize nor malloc() when using a static buffer. 1126 If the object requires more memory than available, 1127 zstd will just error out (typically ZSTD_error_memory_allocation). 1128 Note 2 : there is no corresponding "free" function. 1129 Since workspace is allocated externally, it must be freed externally too. 1130 Note 3 : cParams : use ZSTD_getCParams() to convert a compression level 1131 into its associated cParams. 1132 Limitation 1 : currently not compatible with internal dictionary creation, triggered by 1133 ZSTD_CCtx_loadDictionary(), ZSTD_initCStream_usingDict() or ZSTD_initDStream_usingDict(). 1134 Limitation 2 : static cctx currently not compatible with multi-threading. 1135 Limitation 3 : static dctx is incompatible with legacy support. 1136 1137</p></pre><BR> 1138 1139<pre><b>ZSTD_DStream* ZSTD_initStaticDStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticDCtx() */<b> 1140</b></pre><BR> 1141<pre><b>typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size); 1142typedef void (*ZSTD_freeFunction) (void* opaque, void* address); 1143typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem; 1144static ZSTD_customMem const ZSTD_defaultCMem = { NULL, NULL, NULL }; </b>/**< this constant defers to stdlib's functions */<b> 1145</b><p> These prototypes make it possible to pass your own allocation/free functions. 1146 ZSTD_customMem is provided at creation time, using ZSTD_create*_advanced() variants listed below. 1147 All allocation/free operations will be completed using these custom variants instead of regular <stdlib.h> ones. 1148 1149</p></pre><BR> 1150 1151<a name="Chapter17"></a><h2>Advanced compression functions</h2><pre></pre> 1152 1153<pre><b>ZSTD_CDict* ZSTD_createCDict_byReference(const void* dictBuffer, size_t dictSize, int compressionLevel); 1154</b><p> Create a digested dictionary for compression 1155 Dictionary content is just referenced, not duplicated. 1156 As a consequence, `dictBuffer` **must** outlive CDict, 1157 and its content must remain unmodified throughout the lifetime of CDict. 1158 note: equivalent to ZSTD_createCDict_advanced(), with dictLoadMethod==ZSTD_dlm_byRef 1159</p></pre><BR> 1160 1161<pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize); 1162</b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize. 1163 `estimatedSrcSize` value is optional, select 0 if not known 1164</p></pre><BR> 1165 1166<pre><b>ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize); 1167</b><p> same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`. 1168 All fields of `ZSTD_frameParameters` are set to default : contentSize=1, checksum=0, noDictID=0 1169</p></pre><BR> 1170 1171<pre><b>size_t ZSTD_checkCParams(ZSTD_compressionParameters params); 1172</b><p> Ensure param values remain within authorized range. 1173 @return 0 on success, or an error code (can be checked with ZSTD_isError()) 1174</p></pre><BR> 1175 1176<pre><b>ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize); 1177</b><p> optimize params for a given `srcSize` and `dictSize`. 1178 `srcSize` can be unknown, in which case use ZSTD_CONTENTSIZE_UNKNOWN. 1179 `dictSize` must be `0` when there is no dictionary. 1180 cPar can be invalid : all parameters will be clamped within valid range in the @return struct. 1181 This function never fails (wide contract) 1182</p></pre><BR> 1183 1184<pre><b>size_t ZSTD_compress_advanced(ZSTD_CCtx* cctx, 1185 void* dst, size_t dstCapacity, 1186 const void* src, size_t srcSize, 1187 const void* dict,size_t dictSize, 1188 ZSTD_parameters params); 1189</b><p> Note : this function is now DEPRECATED. 1190 It can be replaced by ZSTD_compress2(), in combination with ZSTD_CCtx_setParameter() and other parameter setters. 1191 This prototype will be marked as deprecated and generate compilation warning on reaching v1.5.x 1192</p></pre><BR> 1193 1194<pre><b>size_t ZSTD_compress_usingCDict_advanced(ZSTD_CCtx* cctx, 1195 void* dst, size_t dstCapacity, 1196 const void* src, size_t srcSize, 1197 const ZSTD_CDict* cdict, 1198 ZSTD_frameParameters fParams); 1199</b><p> Note : this function is now REDUNDANT. 1200 It can be replaced by ZSTD_compress2(), in combination with ZSTD_CCtx_loadDictionary() and other parameter setters. 1201 This prototype will be marked as deprecated and generate compilation warning in some future version 1202</p></pre><BR> 1203 1204<pre><b>size_t ZSTD_CCtx_loadDictionary_byReference(ZSTD_CCtx* cctx, const void* dict, size_t dictSize); 1205</b><p> Same as ZSTD_CCtx_loadDictionary(), but dictionary content is referenced, instead of being copied into CCtx. 1206 It saves some memory, but also requires that `dict` outlives its usage within `cctx` 1207</p></pre><BR> 1208 1209<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); 1210</b><p> Same as ZSTD_CCtx_loadDictionary(), but gives finer control over 1211 how to load the dictionary (by copy ? by reference ?) 1212 and how to interpret it (automatic ? force raw mode ? full mode only ?) 1213</p></pre><BR> 1214 1215<pre><b>size_t ZSTD_CCtx_refPrefix_advanced(ZSTD_CCtx* cctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType); 1216</b><p> Same as ZSTD_CCtx_refPrefix(), but gives finer control over 1217 how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?) 1218</p></pre><BR> 1219 1220<pre><b>size_t ZSTD_CCtx_getParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int* value); 1221</b><p> Get the requested compression parameter value, selected by enum ZSTD_cParameter, 1222 and store it into int* value. 1223 @return : 0, or an error code (which can be tested with ZSTD_isError()). 1224 1225</p></pre><BR> 1226 1227<pre><b>ZSTD_CCtx_params* ZSTD_createCCtxParams(void); 1228size_t ZSTD_freeCCtxParams(ZSTD_CCtx_params* params); 1229</b><p> Quick howto : 1230 - ZSTD_createCCtxParams() : Create a ZSTD_CCtx_params structure 1231 - ZSTD_CCtxParams_setParameter() : Push parameters one by one into 1232 an existing ZSTD_CCtx_params structure. 1233 This is similar to 1234 ZSTD_CCtx_setParameter(). 1235 - ZSTD_CCtx_setParametersUsingCCtxParams() : Apply parameters to 1236 an existing CCtx. 1237 These parameters will be applied to 1238 all subsequent frames. 1239 - ZSTD_compressStream2() : Do compression using the CCtx. 1240 - ZSTD_freeCCtxParams() : Free the memory. 1241 1242 This can be used with ZSTD_estimateCCtxSize_advanced_usingCCtxParams() 1243 for static allocation of CCtx for single-threaded compression. 1244 1245</p></pre><BR> 1246 1247<pre><b>size_t ZSTD_CCtxParams_reset(ZSTD_CCtx_params* params); 1248</b><p> Reset params to default values. 1249 1250</p></pre><BR> 1251 1252<pre><b>size_t ZSTD_CCtxParams_init(ZSTD_CCtx_params* cctxParams, int compressionLevel); 1253</b><p> Initializes the compression parameters of cctxParams according to 1254 compression level. All other parameters are reset to their default values. 1255 1256</p></pre><BR> 1257 1258<pre><b>size_t ZSTD_CCtxParams_init_advanced(ZSTD_CCtx_params* cctxParams, ZSTD_parameters params); 1259</b><p> Initializes the compression and frame parameters of cctxParams according to 1260 params. All other parameters are reset to their default values. 1261 1262</p></pre><BR> 1263 1264<pre><b>size_t ZSTD_CCtxParams_setParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int value); 1265</b><p> Similar to ZSTD_CCtx_setParameter. 1266 Set one compression parameter, selected by enum ZSTD_cParameter. 1267 Parameters must be applied to a ZSTD_CCtx using ZSTD_CCtx_setParametersUsingCCtxParams(). 1268 @result : 0, or an error code (which can be tested with ZSTD_isError()). 1269 1270</p></pre><BR> 1271 1272<pre><b>size_t ZSTD_CCtxParams_getParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int* value); 1273</b><p> Similar to ZSTD_CCtx_getParameter. 1274 Get the requested value of one compression parameter, selected by enum ZSTD_cParameter. 1275 @result : 0, or an error code (which can be tested with ZSTD_isError()). 1276 1277</p></pre><BR> 1278 1279<pre><b>size_t ZSTD_CCtx_setParametersUsingCCtxParams( 1280 ZSTD_CCtx* cctx, const ZSTD_CCtx_params* params); 1281</b><p> Apply a set of ZSTD_CCtx_params to the compression context. 1282 This can be done even after compression is started, 1283 if nbWorkers==0, this will have no impact until a new compression is started. 1284 if nbWorkers>=1, new parameters will be picked up at next job, 1285 with a few restrictions (windowLog, pledgedSrcSize, nbWorkers, jobSize, and overlapLog are not updated). 1286 1287</p></pre><BR> 1288 1289<pre><b>size_t ZSTD_compressStream2_simpleArgs ( 1290 ZSTD_CCtx* cctx, 1291 void* dst, size_t dstCapacity, size_t* dstPos, 1292 const void* src, size_t srcSize, size_t* srcPos, 1293 ZSTD_EndDirective endOp); 1294</b><p> Same as ZSTD_compressStream2(), 1295 but using only integral types as arguments. 1296 This variant might be helpful for binders from dynamic languages 1297 which have troubles handling structures containing memory pointers. 1298 1299</p></pre><BR> 1300 1301<a name="Chapter18"></a><h2>Advanced decompression functions</h2><pre></pre> 1302 1303<pre><b>unsigned ZSTD_isFrame(const void* buffer, size_t size); 1304</b><p> Tells if the content of `buffer` starts with a valid Frame Identifier. 1305 Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0. 1306 Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled. 1307 Note 3 : Skippable Frame Identifiers are considered valid. 1308</p></pre><BR> 1309 1310<pre><b>ZSTD_DDict* ZSTD_createDDict_byReference(const void* dictBuffer, size_t dictSize); 1311</b><p> Create a digested dictionary, ready to start decompression operation without startup delay. 1312 Dictionary content is referenced, and therefore stays in dictBuffer. 1313 It is important that dictBuffer outlives DDict, 1314 it must remain read accessible throughout the lifetime of DDict 1315</p></pre><BR> 1316 1317<pre><b>size_t ZSTD_DCtx_loadDictionary_byReference(ZSTD_DCtx* dctx, const void* dict, size_t dictSize); 1318</b><p> Same as ZSTD_DCtx_loadDictionary(), 1319 but references `dict` content instead of copying it into `dctx`. 1320 This saves memory if `dict` remains around., 1321 However, it's imperative that `dict` remains accessible (and unmodified) while being used, so it must outlive decompression. 1322</p></pre><BR> 1323 1324<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); 1325</b><p> Same as ZSTD_DCtx_loadDictionary(), 1326 but gives direct control over 1327 how to load the dictionary (by copy ? by reference ?) 1328 and how to interpret it (automatic ? force raw mode ? full mode only ?). 1329</p></pre><BR> 1330 1331<pre><b>size_t ZSTD_DCtx_refPrefix_advanced(ZSTD_DCtx* dctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType); 1332</b><p> Same as ZSTD_DCtx_refPrefix(), but gives finer control over 1333 how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?) 1334</p></pre><BR> 1335 1336<pre><b>size_t ZSTD_DCtx_setMaxWindowSize(ZSTD_DCtx* dctx, size_t maxWindowSize); 1337</b><p> Refuses allocating internal buffers for frames requiring a window size larger than provided limit. 1338 This protects a decoder context from reserving too much memory for itself (potential attack scenario). 1339 This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode. 1340 By default, a decompression context accepts all window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT) 1341 @return : 0, or an error code (which can be tested using ZSTD_isError()). 1342 1343</p></pre><BR> 1344 1345<pre><b>size_t ZSTD_DCtx_setFormat(ZSTD_DCtx* dctx, ZSTD_format_e format); 1346</b><p> Instruct the decoder context about what kind of data to decode next. 1347 This instruction is mandatory to decode data without a fully-formed header, 1348 such ZSTD_f_zstd1_magicless for example. 1349 @return : 0, or an error code (which can be tested using ZSTD_isError()). 1350</p></pre><BR> 1351 1352<pre><b>size_t ZSTD_decompressStream_simpleArgs ( 1353 ZSTD_DCtx* dctx, 1354 void* dst, size_t dstCapacity, size_t* dstPos, 1355 const void* src, size_t srcSize, size_t* srcPos); 1356</b><p> Same as ZSTD_decompressStream(), 1357 but using only integral types as arguments. 1358 This can be helpful for binders from dynamic languages 1359 which have troubles handling structures containing memory pointers. 1360 1361</p></pre><BR> 1362 1363<a name="Chapter19"></a><h2>Advanced streaming functions</h2><pre> Warning : most of these functions are now redundant with the Advanced API. 1364 Once Advanced API reaches "stable" status, 1365 redundant functions will be deprecated, and then at some point removed. 1366<BR></pre> 1367 1368<h3>Advanced Streaming compression functions</h3><pre></pre><b><pre></b>/**! ZSTD_initCStream_srcSize() :<b> 1369 * This function is deprecated, and equivalent to: 1370 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1371 * ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any) 1372 * ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel); 1373 * ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1374 * 1375 * pledgedSrcSize must be correct. If it is not known at init time, use 1376 * ZSTD_CONTENTSIZE_UNKNOWN. Note that, for compatibility with older programs, 1377 * "0" also disables frame content size field. It may be enabled in the future. 1378 * Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x 1379 */ 1380size_t 1381ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, 1382 int compressionLevel, 1383 unsigned long long pledgedSrcSize); 1384</pre></b><BR> 1385<a name="Chapter20"></a><h2>! ZSTD_initCStream_usingDict() :</h2><pre> This function is deprecated, and is equivalent to: 1386 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1387 ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel); 1388 ZSTD_CCtx_loadDictionary(zcs, dict, dictSize); 1389 1390 Creates of an internal CDict (incompatible with static CCtx), except if 1391 dict == NULL or dictSize < 8, in which case no dict is used. 1392 Note: dict is loaded with ZSTD_dct_auto (treated as a full zstd dictionary if 1393 it begins with ZSTD_MAGIC_DICTIONARY, else as raw content) and ZSTD_dlm_byCopy. 1394 Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x 1395 1396<BR></pre> 1397 1398<a name="Chapter21"></a><h2>! ZSTD_initCStream_advanced() :</h2><pre> This function is deprecated, and is approximately equivalent to: 1399 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1400 // Pseudocode: Set each zstd parameter and leave the rest as-is. 1401 for ((param, value) : params) { 1402 ZSTD_CCtx_setParameter(zcs, param, value); 1403 } 1404 ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1405 ZSTD_CCtx_loadDictionary(zcs, dict, dictSize); 1406 1407 dict is loaded with ZSTD_dct_auto and ZSTD_dlm_byCopy. 1408 pledgedSrcSize must be correct. 1409 If srcSize is not known at init time, use value ZSTD_CONTENTSIZE_UNKNOWN. 1410 Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x 1411 1412<BR></pre> 1413 1414<a name="Chapter22"></a><h2>! ZSTD_initCStream_usingCDict() :</h2><pre> This function is deprecated, and equivalent to: 1415 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1416 ZSTD_CCtx_refCDict(zcs, cdict); 1417 1418 note : cdict will just be referenced, and must outlive compression session 1419 Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x 1420 1421<BR></pre> 1422 1423<a name="Chapter23"></a><h2>! ZSTD_initCStream_usingCDict_advanced() :</h2><pre> This function is DEPRECATED, and is approximately equivalent to: 1424 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1425 // Pseudocode: Set each zstd frame parameter and leave the rest as-is. 1426 for ((fParam, value) : fParams) { 1427 ZSTD_CCtx_setParameter(zcs, fParam, value); 1428 } 1429 ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1430 ZSTD_CCtx_refCDict(zcs, cdict); 1431 1432 same as ZSTD_initCStream_usingCDict(), with control over frame parameters. 1433 pledgedSrcSize must be correct. If srcSize is not known at init time, use 1434 value ZSTD_CONTENTSIZE_UNKNOWN. 1435 Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x 1436 1437<BR></pre> 1438 1439<pre><b>size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize); 1440</b><p> This function is deprecated, and is equivalent to: 1441 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1442 ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1443 1444 start a new frame, using same parameters from previous frame. 1445 This is typically useful to skip dictionary loading stage, since it will re-use it in-place. 1446 Note that zcs must be init at least once before using ZSTD_resetCStream(). 1447 If pledgedSrcSize is not known at reset time, use macro ZSTD_CONTENTSIZE_UNKNOWN. 1448 If pledgedSrcSize > 0, its value must be correct, as it will be written in header, and controlled at the end. 1449 For the time being, pledgedSrcSize==0 is interpreted as "srcSize unknown" for compatibility with older programs, 1450 but it will change to mean "empty" in future version, so use macro ZSTD_CONTENTSIZE_UNKNOWN instead. 1451 @return : 0, or an error code (which can be tested using ZSTD_isError()) 1452 Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x 1453 1454</p></pre><BR> 1455 1456<pre><b>typedef struct { 1457 unsigned long long ingested; </b>/* nb input bytes read and buffered */<b> 1458 unsigned long long consumed; </b>/* nb input bytes actually compressed */<b> 1459 unsigned long long produced; </b>/* nb of compressed bytes generated and buffered */<b> 1460 unsigned long long flushed; </b>/* nb of compressed bytes flushed : not provided; can be tracked from caller side */<b> 1461 unsigned currentJobID; </b>/* MT only : latest started job nb */<b> 1462 unsigned nbActiveWorkers; </b>/* MT only : nb of workers actively compressing at probe time */<b> 1463} ZSTD_frameProgression; 1464</b></pre><BR> 1465<pre><b>size_t ZSTD_toFlushNow(ZSTD_CCtx* cctx); 1466</b><p> Tell how many bytes are ready to be flushed immediately. 1467 Useful for multithreading scenarios (nbWorkers >= 1). 1468 Probe the oldest active job, defined as oldest job not yet entirely flushed, 1469 and check its output buffer. 1470 @return : amount of data stored in oldest job and ready to be flushed immediately. 1471 if @return == 0, it means either : 1472 + there is no active job (could be checked with ZSTD_frameProgression()), or 1473 + oldest job is still actively compressing data, 1474 but everything it has produced has also been flushed so far, 1475 therefore flush speed is limited by production speed of oldest job 1476 irrespective of the speed of concurrent (and newer) jobs. 1477 1478</p></pre><BR> 1479 1480<h3>Advanced Streaming decompression functions</h3><pre></pre><b><pre></b>/**<b> 1481 * This function is deprecated, and is equivalent to: 1482 * 1483 * ZSTD_DCtx_reset(zds, ZSTD_reset_session_only); 1484 * ZSTD_DCtx_loadDictionary(zds, dict, dictSize); 1485 * 1486 * note: no dictionary will be used if dict == NULL or dictSize < 8 1487 * Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x 1488 */ 1489size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize); 1490</pre></b><BR> 1491<a name="Chapter24"></a><h2>This function is deprecated, and is equivalent to:</h2><pre> 1492 ZSTD_DCtx_reset(zds, ZSTD_reset_session_only); 1493 ZSTD_DCtx_refDDict(zds, ddict); 1494 1495 note : ddict is referenced, it must outlive decompression session 1496 Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x 1497 1498<BR></pre> 1499 1500<a name="Chapter25"></a><h2>This function is deprecated, and is equivalent to:</h2><pre> 1501 ZSTD_DCtx_reset(zds, ZSTD_reset_session_only); 1502 1503 re-use decompression parameters from previous init; saves dictionary loading 1504 Note : this prototype will be marked as deprecated and generate compilation warnings on reaching v1.5.x 1505 1506<BR></pre> 1507 1508<a name="Chapter26"></a><h2>Buffer-less and synchronous inner streaming functions</h2><pre> 1509 This is an advanced API, giving full control over buffer management, for users which need direct control over memory. 1510 But it's also a complex one, with several restrictions, documented below. 1511 Prefer normal streaming API for an easier experience. 1512 1513<BR></pre> 1514 1515<a name="Chapter27"></a><h2>Buffer-less streaming compression (synchronous mode)</h2><pre> 1516 A ZSTD_CCtx object is required to track streaming operations. 1517 Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource. 1518 ZSTD_CCtx object can be re-used multiple times within successive compression operations. 1519 1520 Start by initializing a context. 1521 Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression, 1522 or ZSTD_compressBegin_advanced(), for finer parameter control. 1523 It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx() 1524 1525 Then, consume your input using ZSTD_compressContinue(). 1526 There are some important considerations to keep in mind when using this advanced function : 1527 - ZSTD_compressContinue() has no internal buffer. It uses externally provided buffers only. 1528 - Interface is synchronous : input is consumed entirely and produces 1+ compressed blocks. 1529 - Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario. 1530 Worst case evaluation is provided by ZSTD_compressBound(). 1531 ZSTD_compressContinue() doesn't guarantee recover after a failed compression. 1532 - ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog). 1533 It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks) 1534 - ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps. 1535 In which case, it will "discard" the relevant memory section from its history. 1536 1537 Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum. 1538 It's possible to use srcSize==0, in which case, it will write a final empty block to end the frame. 1539 Without last block mark, frames are considered unfinished (hence corrupted) by compliant decoders. 1540 1541 `ZSTD_CCtx` object can be re-used (ZSTD_compressBegin()) to compress again. 1542<BR></pre> 1543 1544<h3>Buffer-less streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel); 1545size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel); 1546size_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> 1547size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); </b>/**< note: fails if cdict==NULL */<b> 1548size_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> 1549size_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> 1550</pre></b><BR> 1551<a name="Chapter28"></a><h2>Buffer-less streaming decompression (synchronous mode)</h2><pre> 1552 A ZSTD_DCtx object is required to track streaming operations. 1553 Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it. 1554 A ZSTD_DCtx object can be re-used multiple times. 1555 1556 First typical operation is to retrieve frame parameters, using ZSTD_getFrameHeader(). 1557 Frame header is extracted from the beginning of compressed frame, so providing only the frame's beginning is enough. 1558 Data fragment must be large enough to ensure successful decoding. 1559 `ZSTD_frameHeaderSize_max` bytes is guaranteed to always be large enough. 1560 @result : 0 : successful decoding, the `ZSTD_frameHeader` structure is correctly filled. 1561 >0 : `srcSize` is too small, please provide at least @result bytes on next attempt. 1562 errorCode, which can be tested using ZSTD_isError(). 1563 1564 It fills a ZSTD_frameHeader structure with important information to correctly decode the frame, 1565 such as the dictionary ID, content size, or maximum back-reference distance (`windowSize`). 1566 Note that these values could be wrong, either because of data corruption, or because a 3rd party deliberately spoofs false information. 1567 As a consequence, check that values remain within valid application range. 1568 For example, do not allocate memory blindly, check that `windowSize` is within expectation. 1569 Each application can set its own limits, depending on local restrictions. 1570 For extended interoperability, it is recommended to support `windowSize` of at least 8 MB. 1571 1572 ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize` bytes. 1573 ZSTD_decompressContinue() is very sensitive to contiguity, 1574 if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place, 1575 or that previous contiguous segment is large enough to properly handle maximum back-reference distance. 1576 There are multiple ways to guarantee this condition. 1577 1578 The most memory efficient way is to use a round buffer of sufficient size. 1579 Sufficient size is determined by invoking ZSTD_decodingBufferSize_min(), 1580 which can @return an error code if required value is too large for current system (in 32-bits mode). 1581 In a round buffer methodology, ZSTD_decompressContinue() decompresses each block next to previous one, 1582 up to the moment there is not enough room left in the buffer to guarantee decoding another full block, 1583 which maximum size is provided in `ZSTD_frameHeader` structure, field `blockSizeMax`. 1584 At which point, decoding can resume from the beginning of the buffer. 1585 Note that already decoded data stored in the buffer should be flushed before being overwritten. 1586 1587 There are alternatives possible, for example using two or more buffers of size `windowSize` each, though they consume more memory. 1588 1589 Finally, if you control the compression process, you can also ignore all buffer size rules, 1590 as long as the encoder and decoder progress in "lock-step", 1591 aka use exactly the same buffer sizes, break contiguity at the same place, etc. 1592 1593 Once buffers are setup, start decompression, with ZSTD_decompressBegin(). 1594 If decompression requires a dictionary, use ZSTD_decompressBegin_usingDict() or ZSTD_decompressBegin_usingDDict(). 1595 1596 Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively. 1597 ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue(). 1598 ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail. 1599 1600 @result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity). 1601 It can be zero : it just means ZSTD_decompressContinue() has decoded some metadata item. 1602 It can also be an error code, which can be tested with ZSTD_isError(). 1603 1604 A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero. 1605 Context can then be reset to start a new decompression. 1606 1607 Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType(). 1608 This information is not required to properly decode a frame. 1609 1610 == Special case : skippable frames 1611 1612 Skippable frames allow integration of user-defined data into a flow of concatenated frames. 1613 Skippable frames will be ignored (skipped) by decompressor. 1614 The format of skippable frames is as follows : 1615 a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F 1616 b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits 1617 c) Frame Content - any content (User Data) of length equal to Frame Size 1618 For skippable frames ZSTD_getFrameHeader() returns zfhPtr->frameType==ZSTD_skippableFrame. 1619 For skippable frames ZSTD_decompressContinue() always returns 0 : it only skips the content. 1620<BR></pre> 1621 1622<h3>Buffer-less streaming decompression functions</h3><pre></pre><b><pre>typedef enum { ZSTD_frame, ZSTD_skippableFrame } ZSTD_frameType_e; 1623typedef struct { 1624 unsigned long long frameContentSize; </b>/* if == ZSTD_CONTENTSIZE_UNKNOWN, it means this field is not available. 0 means "empty" */<b> 1625 unsigned long long windowSize; </b>/* can be very large, up to <= frameContentSize */<b> 1626 unsigned blockSizeMax; 1627 ZSTD_frameType_e frameType; </b>/* if == ZSTD_skippableFrame, frameContentSize is the size of skippable content */<b> 1628 unsigned headerSize; 1629 unsigned dictID; 1630 unsigned checksumFlag; 1631} ZSTD_frameHeader; 1632</pre></b><BR> 1633<pre><b>size_t ZSTD_getFrameHeader(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize); </b>/**< doesn't consume input */<b> 1634</b>/*! ZSTD_getFrameHeader_advanced() :<b> 1635 * same as ZSTD_getFrameHeader(), 1636 * with added capability to select a format (like ZSTD_f_zstd1_magicless) */ 1637size_t ZSTD_getFrameHeader_advanced(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize, ZSTD_format_e format); 1638size_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> 1639</b><p> decode Frame Header, or requires larger `srcSize`. 1640 @return : 0, `zfhPtr` is correctly filled, 1641 >0, `srcSize` is too small, value is wanted `srcSize` amount, 1642 or an error code, which can be tested using ZSTD_isError() 1643</p></pre><BR> 1644 1645<pre><b>typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e; 1646</b></pre><BR> 1647<a name="Chapter29"></a><h2>Block level API</h2><pre></pre> 1648 1649<pre><b></b><p> Frame metadata cost is typically ~12 bytes, which can be non-negligible for very small blocks (< 100 bytes). 1650 But users will have to take in charge needed metadata to regenerate data, such as compressed and content sizes. 1651 1652 A few rules to respect : 1653 - Compressing and decompressing require a context structure 1654 + Use ZSTD_createCCtx() and ZSTD_createDCtx() 1655 - It is necessary to init context before starting 1656 + compression : any ZSTD_compressBegin*() variant, including with dictionary 1657 + decompression : any ZSTD_decompressBegin*() variant, including with dictionary 1658 + copyCCtx() and copyDCtx() can be used too 1659 - Block size is limited, it must be <= ZSTD_getBlockSize() <= ZSTD_BLOCKSIZE_MAX == 128 KB 1660 + If input is larger than a block size, it's necessary to split input data into multiple blocks 1661 + For inputs larger than a single block, consider using regular ZSTD_compress() instead. 1662 Frame metadata is not that costly, and quickly becomes negligible as source size grows larger than a block. 1663 - When a block is considered not compressible enough, ZSTD_compressBlock() result will be 0 (zero) ! 1664 ===> In which case, nothing is produced into `dst` ! 1665 + User __must__ test for such outcome and deal directly with uncompressed data 1666 + A block cannot be declared incompressible if ZSTD_compressBlock() return value was != 0. 1667 Doing so would mess up with statistics history, leading to potential data corruption. 1668 + ZSTD_decompressBlock() _doesn't accept uncompressed data as input_ !! 1669 + In case of multiple successive blocks, should some of them be uncompressed, 1670 decoder must be informed of their existence in order to follow proper history. 1671 Use ZSTD_insertBlock() for such a case. 1672</p></pre><BR> 1673 1674<h3>Raw zstd block functions</h3><pre></pre><b><pre>size_t ZSTD_getBlockSize (const ZSTD_CCtx* cctx); 1675size_t ZSTD_compressBlock (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize); 1676size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize); 1677size_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> 1678</pre></b><BR> 1679</html> 1680</body> 1681