1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 4<title>zstd 1.4.0 Manual</title> 5</head> 6<body> 7<h1>zstd 1.4.0 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">Default constant</a></li> 14<li><a href="#Chapter4">Constants</a></li> 15<li><a href="#Chapter5">Simple API</a></li> 16<li><a href="#Chapter6">Explicit context</a></li> 17<li><a href="#Chapter7">Advanced compression API</a></li> 18<li><a href="#Chapter8">Advanced decompression API</a></li> 19<li><a href="#Chapter9">Streaming</a></li> 20<li><a href="#Chapter10">Streaming compression - HowTo</a></li> 21<li><a href="#Chapter11">This is a legacy streaming API, and can be replaced by ZSTD_CCtx_reset() and</a></li> 22<li><a href="#Chapter12">Equivalent to:</a></li> 23<li><a href="#Chapter13">Alternative for ZSTD_compressStream2(zcs, output, input, ZSTD_e_continue).</a></li> 24<li><a href="#Chapter14">Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_flush).</a></li> 25<li><a href="#Chapter15">Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_end).</a></li> 26<li><a href="#Chapter16">Streaming decompression - HowTo</a></li> 27<li><a href="#Chapter17">Simple dictionary API</a></li> 28<li><a href="#Chapter18">Bulk processing dictionary API</a></li> 29<li><a href="#Chapter19">Dictionary helper functions</a></li> 30<li><a href="#Chapter20">Advanced dictionary and prefix API</a></li> 31<li><a href="#Chapter21">ADVANCED AND EXPERIMENTAL FUNCTIONS</a></li> 32<li><a href="#Chapter22">experimental API (static linking only)</a></li> 33<li><a href="#Chapter23">Frame size functions</a></li> 34<li><a href="#Chapter24">ZSTD_decompressBound() :</a></li> 35<li><a href="#Chapter25">Memory management</a></li> 36<li><a href="#Chapter26">Advanced compression functions</a></li> 37<li><a href="#Chapter27">Advanced decompression functions</a></li> 38<li><a href="#Chapter28">Advanced streaming functions</a></li> 39<li><a href="#Chapter29">Buffer-less and synchronous inner streaming functions</a></li> 40<li><a href="#Chapter30">Buffer-less streaming compression (synchronous mode)</a></li> 41<li><a href="#Chapter31">Buffer-less streaming decompression (synchronous mode)</a></li> 42<li><a href="#Chapter32">ZSTD_getFrameHeader() :</a></li> 43<li><a href="#Chapter33">Block level API</a></li> 44</ol> 45<hr> 46<a name="Chapter1"></a><h2>Introduction</h2><pre> 47 zstd, short for Zstandard, is a fast lossless compression algorithm, targeting 48 real-time compression scenarios at zlib-level and better compression ratios. 49 The zstd compression library provides in-memory compression and decompression 50 functions. 51 52 The library supports regular compression levels from 1 up to ZSTD_maxCLevel(), 53 which is currently 22. Levels >= 20, labeled `--ultra`, should be used with 54 caution, as they require more memory. The library also offers negative 55 compression levels, which extend the range of speed vs. ratio preferences. 56 The lower the level, the faster the speed (at the cost of compression). 57 58 Compression can be done in: 59 - a single step (described as Simple API) 60 - a single step, reusing a context (described as Explicit context) 61 - unbounded multiple steps (described as Streaming compression) 62 63 The compression ratio achievable on small data can be highly improved using 64 a dictionary. Dictionary compression can be performed in: 65 - a single step (described as Simple dictionary API) 66 - a single step, reusing a dictionary (described as Bulk-processing 67 dictionary API) 68 69 Advanced experimental functions can be accessed using 70 `#define ZSTD_STATIC_LINKING_ONLY` before including zstd.h. 71 72 Advanced experimental APIs should never be used with a dynamically-linked 73 library. They are not "stable"; their definitions or signatures may change in 74 the future. Only static linking is allowed. 75<BR></pre> 76 77<a name="Chapter2"></a><h2>Version</h2><pre></pre> 78 79<pre><b>unsigned ZSTD_versionNumber(void); </b>/**< to check runtime library version */<b> 80</b></pre><BR> 81<a name="Chapter3"></a><h2>Default constant</h2><pre></pre> 82 83<a name="Chapter4"></a><h2>Constants</h2><pre></pre> 84 85<a name="Chapter5"></a><h2>Simple API</h2><pre></pre> 86 87<pre><b>size_t ZSTD_compress( void* dst, size_t dstCapacity, 88 const void* src, size_t srcSize, 89 int compressionLevel); 90</b><p> Compresses `src` content as a single zstd compressed frame into already allocated `dst`. 91 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`. 92 @return : compressed size written into `dst` (<= `dstCapacity), 93 or an error code if it fails (which can be tested using ZSTD_isError()). 94</p></pre><BR> 95 96<pre><b>size_t ZSTD_decompress( void* dst, size_t dstCapacity, 97 const void* src, size_t compressedSize); 98</b><p> `compressedSize` : must be the _exact_ size of some number of compressed and/or skippable frames. 99 `dstCapacity` is an upper bound of originalSize to regenerate. 100 If user cannot imply a maximum upper bound, it's better to use streaming mode to decompress data. 101 @return : the number of bytes decompressed into `dst` (<= `dstCapacity`), 102 or an errorCode if it fails (which can be tested using ZSTD_isError()). 103</p></pre><BR> 104 105<pre><b>#define ZSTD_CONTENTSIZE_UNKNOWN (0ULL - 1) 106#define ZSTD_CONTENTSIZE_ERROR (0ULL - 2) 107unsigned long long ZSTD_getFrameContentSize(const void *src, size_t srcSize); 108</b><p> `src` should point to the start of a ZSTD encoded frame. 109 `srcSize` must be at least as large as the frame header. 110 hint : any size >= `ZSTD_frameHeaderSize_max` is large enough. 111 @return : - decompressed size of `src` frame content, if known 112 - ZSTD_CONTENTSIZE_UNKNOWN if the size cannot be determined 113 - ZSTD_CONTENTSIZE_ERROR if an error occurred (e.g. invalid magic number, srcSize too small) 114 note 1 : a 0 return value means the frame is valid but "empty". 115 note 2 : decompressed size is an optional field, it may not be present, typically in streaming mode. 116 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size. 117 In which case, it's necessary to use streaming mode to decompress data. 118 Optionally, application can rely on some implicit limit, 119 as ZSTD_decompress() only needs an upper bound of decompressed size. 120 (For example, data could be necessarily cut into blocks <= 16 KB). 121 note 3 : decompressed size is always present when compression is completed using single-pass functions, 122 such as ZSTD_compress(), ZSTD_compressCCtx() ZSTD_compress_usingDict() or ZSTD_compress_usingCDict(). 123 note 4 : decompressed size can be very large (64-bits value), 124 potentially larger than what local system can handle as a single memory segment. 125 In which case, it's necessary to use streaming mode to decompress data. 126 note 5 : If source is untrusted, decompressed size could be wrong or intentionally modified. 127 Always ensure return value fits within application's authorized limits. 128 Each application can set its own limits. 129 note 6 : This function replaces ZSTD_getDecompressedSize() 130</p></pre><BR> 131 132<pre><b>unsigned long long ZSTD_getDecompressedSize(const void* src, size_t srcSize); 133</b><p> NOTE: This function is now obsolete, in favor of ZSTD_getFrameContentSize(). 134 Both functions work the same way, but ZSTD_getDecompressedSize() blends 135 "empty", "unknown" and "error" results to the same return value (0), 136 while ZSTD_getFrameContentSize() gives them separate return values. 137 @return : decompressed size of `src` frame content _if known and not empty_, 0 otherwise. 138</p></pre><BR> 139 140<pre><b>size_t ZSTD_findFrameCompressedSize(const void* src, size_t srcSize); 141</b><p> `src` should point to the start of a ZSTD frame or skippable frame. 142 `srcSize` must be >= first frame size 143 @return : the compressed size of the first frame starting at `src`, 144 suitable to pass as `srcSize` to `ZSTD_decompress` or similar, 145 or an error code if input is invalid 146</p></pre><BR> 147 148<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> 149size_t ZSTD_compressBound(size_t srcSize); </b>/*!< maximum compressed size in worst case single-pass scenario */<b> 150unsigned ZSTD_isError(size_t code); </b>/*!< tells if a `size_t` function result is an error code */<b> 151const char* ZSTD_getErrorName(size_t code); </b>/*!< provides readable string from an error code */<b> 152int ZSTD_minCLevel(void); </b>/*!< minimum negative compression level allowed */<b> 153int ZSTD_maxCLevel(void); </b>/*!< maximum compression level available */<b> 154</pre></b><BR> 155<a name="Chapter6"></a><h2>Explicit context</h2><pre></pre> 156 157<h3>Compression context</h3><pre> When compressing many times, 158 it is recommended to allocate a context just once, and re-use it for each successive compression operation. 159 This will make workload friendlier for system's memory. 160 Use one context per thread for parallel execution in multi-threaded environments. 161</pre><b><pre>typedef struct ZSTD_CCtx_s ZSTD_CCtx; 162ZSTD_CCtx* ZSTD_createCCtx(void); 163size_t ZSTD_freeCCtx(ZSTD_CCtx* cctx); 164</pre></b><BR> 165<pre><b>size_t ZSTD_compressCCtx(ZSTD_CCtx* cctx, 166 void* dst, size_t dstCapacity, 167 const void* src, size_t srcSize, 168 int compressionLevel); 169</b><p> Same as ZSTD_compress(), using an explicit ZSTD_CCtx 170 The function will compress at requested compression level, 171 ignoring any other parameter 172</p></pre><BR> 173 174<h3>Decompression context</h3><pre> When decompressing many times, 175 it is recommended to allocate a context only once, 176 and re-use it for each successive compression operation. 177 This will make workload friendlier for system's memory. 178 Use one context per thread for parallel execution. 179</pre><b><pre>typedef struct ZSTD_DCtx_s ZSTD_DCtx; 180ZSTD_DCtx* ZSTD_createDCtx(void); 181size_t ZSTD_freeDCtx(ZSTD_DCtx* dctx); 182</pre></b><BR> 183<pre><b>size_t ZSTD_decompressDCtx(ZSTD_DCtx* dctx, 184 void* dst, size_t dstCapacity, 185 const void* src, size_t srcSize); 186</b><p> Same as ZSTD_decompress(), 187 requires an allocated ZSTD_DCtx. 188 Compatible with sticky parameters. 189 190</p></pre><BR> 191 192<a name="Chapter7"></a><h2>Advanced compression API</h2><pre></pre> 193 194<pre><b>typedef enum { ZSTD_fast=1, 195 ZSTD_dfast=2, 196 ZSTD_greedy=3, 197 ZSTD_lazy=4, 198 ZSTD_lazy2=5, 199 ZSTD_btlazy2=6, 200 ZSTD_btopt=7, 201 ZSTD_btultra=8, 202 ZSTD_btultra2=9 203 </b>/* note : new strategies _might_ be added in the future.<b> 204 Only the order (from fast to strong) is guaranteed */ 205} ZSTD_strategy; 206</b></pre><BR> 207<pre><b>typedef enum { 208 209 </b>/* compression parameters<b> 210 * Note: When compressing with a ZSTD_CDict these parameters are superseded 211 * by the parameters used to construct the ZSTD_CDict. See ZSTD_CCtx_refCDict() 212 * for more info (superseded-by-cdict). */ 213 ZSTD_c_compressionLevel=100, </b>/* Update all compression parameters according to pre-defined cLevel table<b> 214 * Default level is ZSTD_CLEVEL_DEFAULT==3. 215 * Special: value 0 means default, which is controlled by ZSTD_CLEVEL_DEFAULT. 216 * Note 1 : it's possible to pass a negative compression level. 217 * Note 2 : setting a level sets all default values of other compression parameters */ 218 ZSTD_c_windowLog=101, </b>/* Maximum allowed back-reference distance, expressed as power of 2.<b> 219 * Must be clamped between ZSTD_WINDOWLOG_MIN and ZSTD_WINDOWLOG_MAX. 220 * Special: value 0 means "use default windowLog". 221 * Note: Using a windowLog greater than ZSTD_WINDOWLOG_LIMIT_DEFAULT 222 * requires explicitly allowing such window size at decompression stage if using streaming. */ 223 ZSTD_c_hashLog=102, </b>/* Size of the initial probe table, as a power of 2.<b> 224 * Resulting memory usage is (1 << (hashLog+2)). 225 * Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX. 226 * Larger tables improve compression ratio of strategies <= dFast, 227 * and improve speed of strategies > dFast. 228 * Special: value 0 means "use default hashLog". */ 229 ZSTD_c_chainLog=103, </b>/* Size of the multi-probe search table, as a power of 2.<b> 230 * Resulting memory usage is (1 << (chainLog+2)). 231 * Must be clamped between ZSTD_CHAINLOG_MIN and ZSTD_CHAINLOG_MAX. 232 * Larger tables result in better and slower compression. 233 * This parameter is useless when using "fast" strategy. 234 * It's still useful when using "dfast" strategy, 235 * in which case it defines a secondary probe table. 236 * Special: value 0 means "use default chainLog". */ 237 ZSTD_c_searchLog=104, </b>/* Number of search attempts, as a power of 2.<b> 238 * More attempts result in better and slower compression. 239 * This parameter is useless when using "fast" and "dFast" strategies. 240 * Special: value 0 means "use default searchLog". */ 241 ZSTD_c_minMatch=105, </b>/* Minimum size of searched matches.<b> 242 * Note that Zstandard can still find matches of smaller size, 243 * it just tweaks its search algorithm to look for this size and larger. 244 * Larger values increase compression and decompression speed, but decrease ratio. 245 * Must be clamped between ZSTD_MINMATCH_MIN and ZSTD_MINMATCH_MAX. 246 * Note that currently, for all strategies < btopt, effective minimum is 4. 247 * , for all strategies > fast, effective maximum is 6. 248 * Special: value 0 means "use default minMatchLength". */ 249 ZSTD_c_targetLength=106, </b>/* Impact of this field depends on strategy.<b> 250 * For strategies btopt, btultra & btultra2: 251 * Length of Match considered "good enough" to stop search. 252 * Larger values make compression stronger, and slower. 253 * For strategy fast: 254 * Distance between match sampling. 255 * Larger values make compression faster, and weaker. 256 * Special: value 0 means "use default targetLength". */ 257 ZSTD_c_strategy=107, </b>/* See ZSTD_strategy enum definition.<b> 258 * The higher the value of selected strategy, the more complex it is, 259 * resulting in stronger and slower compression. 260 * Special: value 0 means "use default strategy". */ 261 262 </b>/* LDM mode parameters */<b> 263 ZSTD_c_enableLongDistanceMatching=160, </b>/* Enable long distance matching.<b> 264 * This parameter is designed to improve compression ratio 265 * for large inputs, by finding large matches at long distance. 266 * It increases memory usage and window size. 267 * Note: enabling this parameter increases default ZSTD_c_windowLog to 128 MB 268 * except when expressly set to a different value. */ 269 ZSTD_c_ldmHashLog=161, </b>/* Size of the table for long distance matching, as a power of 2.<b> 270 * Larger values increase memory usage and compression ratio, 271 * but decrease compression speed. 272 * Must be clamped between ZSTD_HASHLOG_MIN and ZSTD_HASHLOG_MAX 273 * default: windowlog - 7. 274 * Special: value 0 means "automatically determine hashlog". */ 275 ZSTD_c_ldmMinMatch=162, </b>/* Minimum match size for long distance matcher.<b> 276 * Larger/too small values usually decrease compression ratio. 277 * Must be clamped between ZSTD_LDM_MINMATCH_MIN and ZSTD_LDM_MINMATCH_MAX. 278 * Special: value 0 means "use default value" (default: 64). */ 279 ZSTD_c_ldmBucketSizeLog=163, </b>/* Log size of each bucket in the LDM hash table for collision resolution.<b> 280 * Larger values improve collision resolution but decrease compression speed. 281 * The maximum value is ZSTD_LDM_BUCKETSIZELOG_MAX. 282 * Special: value 0 means "use default value" (default: 3). */ 283 ZSTD_c_ldmHashRateLog=164, </b>/* Frequency of inserting/looking up entries into the LDM hash table.<b> 284 * Must be clamped between 0 and (ZSTD_WINDOWLOG_MAX - ZSTD_HASHLOG_MIN). 285 * Default is MAX(0, (windowLog - ldmHashLog)), optimizing hash table usage. 286 * Larger values improve compression speed. 287 * Deviating far from default value will likely result in a compression ratio decrease. 288 * Special: value 0 means "automatically determine hashRateLog". */ 289 290 </b>/* frame parameters */<b> 291 ZSTD_c_contentSizeFlag=200, </b>/* Content size will be written into frame header _whenever known_ (default:1)<b> 292 * Content size must be known at the beginning of compression. 293 * This is automatically the case when using ZSTD_compress2(), 294 * For streaming variants, content size must be provided with ZSTD_CCtx_setPledgedSrcSize() */ 295 ZSTD_c_checksumFlag=201, </b>/* A 32-bits checksum of content is written at end of frame (default:0) */<b> 296 ZSTD_c_dictIDFlag=202, </b>/* When applicable, dictionary's ID is written into frame header (default:1) */<b> 297 298 </b>/* multi-threading parameters */<b> 299 </b>/* These parameters are only useful if multi-threading is enabled (compiled with build macro ZSTD_MULTITHREAD).<b> 300 * They return an error otherwise. */ 301 ZSTD_c_nbWorkers=400, </b>/* Select how many threads will be spawned to compress in parallel.<b> 302 * When nbWorkers >= 1, triggers asynchronous mode when used with ZSTD_compressStream*() : 303 * ZSTD_compressStream*() consumes input and flush output if possible, but immediately gives back control to caller, 304 * while compression work is performed in parallel, within worker threads. 305 * (note : a strong exception to this rule is when first invocation of ZSTD_compressStream2() sets ZSTD_e_end : 306 * in which case, ZSTD_compressStream2() delegates to ZSTD_compress2(), which is always a blocking call). 307 * More workers improve speed, but also increase memory usage. 308 * Default value is `0`, aka "single-threaded mode" : no worker is spawned, compression is performed inside Caller's thread, all invocations are blocking */ 309 ZSTD_c_jobSize=401, </b>/* Size of a compression job. This value is enforced only when nbWorkers >= 1.<b> 310 * Each compression job is completed in parallel, so this value can indirectly impact the nb of active threads. 311 * 0 means default, which is dynamically determined based on compression parameters. 312 * Job size must be a minimum of overlap size, or 1 MB, whichever is largest. 313 * The minimum size is automatically and transparently enforced */ 314 ZSTD_c_overlapLog=402, </b>/* Control the overlap size, as a fraction of window size.<b> 315 * The overlap size is an amount of data reloaded from previous job at the beginning of a new job. 316 * It helps preserve compression ratio, while each job is compressed in parallel. 317 * This value is enforced only when nbWorkers >= 1. 318 * Larger values increase compression ratio, but decrease speed. 319 * Possible values range from 0 to 9 : 320 * - 0 means "default" : value will be determined by the library, depending on strategy 321 * - 1 means "no overlap" 322 * - 9 means "full overlap", using a full window size. 323 * Each intermediate rank increases/decreases load size by a factor 2 : 324 * 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 325 * default value varies between 6 and 9, depending on strategy */ 326 327 </b>/* note : additional experimental parameters are also available<b> 328 * within the experimental section of the API. 329 * At the time of this writing, they include : 330 * ZSTD_c_rsyncable 331 * ZSTD_c_format 332 * ZSTD_c_forceMaxWindow 333 * ZSTD_c_forceAttachDict 334 * ZSTD_c_literalCompressionMode 335 * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them. 336 * note : never ever use experimentalParam? names directly; 337 * also, the enums values themselves are unstable and can still change. 338 */ 339 ZSTD_c_experimentalParam1=500, 340 ZSTD_c_experimentalParam2=10, 341 ZSTD_c_experimentalParam3=1000, 342 ZSTD_c_experimentalParam4=1001, 343 ZSTD_c_experimentalParam5=1002, 344} ZSTD_cParameter; 345</b></pre><BR> 346<pre><b>typedef struct { 347 size_t error; 348 int lowerBound; 349 int upperBound; 350} ZSTD_bounds; 351</b></pre><BR> 352<pre><b>ZSTD_bounds ZSTD_cParam_getBounds(ZSTD_cParameter cParam); 353</b><p> All parameters must belong to an interval with lower and upper bounds, 354 otherwise they will either trigger an error or be automatically clamped. 355 @return : a structure, ZSTD_bounds, which contains 356 - an error status field, which must be tested using ZSTD_isError() 357 - lower and upper bounds, both inclusive 358 359</p></pre><BR> 360 361<pre><b>size_t ZSTD_CCtx_setParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int value); 362</b><p> Set one compression parameter, selected by enum ZSTD_cParameter. 363 All parameters have valid bounds. Bounds can be queried using ZSTD_cParam_getBounds(). 364 Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter). 365 Setting a parameter is generally only possible during frame initialization (before starting compression). 366 Exception : when using multi-threading mode (nbWorkers >= 1), 367 the following parameters can be updated _during_ compression (within same frame): 368 => compressionLevel, hashLog, chainLog, searchLog, minMatch, targetLength and strategy. 369 new parameters will be active for next job only (after a flush()). 370 @return : an error code (which can be tested using ZSTD_isError()). 371 372</p></pre><BR> 373 374<pre><b>size_t ZSTD_CCtx_setPledgedSrcSize(ZSTD_CCtx* cctx, unsigned long long pledgedSrcSize); 375</b><p> Total input data size to be compressed as a single frame. 376 Value will be written in frame header, unless if explicitly forbidden using ZSTD_c_contentSizeFlag. 377 This value will also be controlled at end of frame, and trigger an error if not respected. 378 @result : 0, or an error code (which can be tested with ZSTD_isError()). 379 Note 1 : pledgedSrcSize==0 actually means zero, aka an empty frame. 380 In order to mean "unknown content size", pass constant ZSTD_CONTENTSIZE_UNKNOWN. 381 ZSTD_CONTENTSIZE_UNKNOWN is default value for any new frame. 382 Note 2 : pledgedSrcSize is only valid once, for the next frame. 383 It's discarded at the end of the frame, and replaced by ZSTD_CONTENTSIZE_UNKNOWN. 384 Note 3 : Whenever all input data is provided and consumed in a single round, 385 for example with ZSTD_compress2(), 386 or invoking immediately ZSTD_compressStream2(,,,ZSTD_e_end), 387 this value is automatically overridden by srcSize instead. 388 389</p></pre><BR> 390 391<pre><b>typedef enum { 392 ZSTD_reset_session_only = 1, 393 ZSTD_reset_parameters = 2, 394 ZSTD_reset_session_and_parameters = 3 395} ZSTD_ResetDirective; 396</b></pre><BR> 397<pre><b>size_t ZSTD_CCtx_reset(ZSTD_CCtx* cctx, ZSTD_ResetDirective reset); 398</b><p> There are 2 different things that can be reset, independently or jointly : 399 - The session : will stop compressing current frame, and make CCtx ready to start a new one. 400 Useful after an error, or to interrupt any ongoing compression. 401 Any internal data not yet flushed is cancelled. 402 Compression parameters and dictionary remain unchanged. 403 They will be used to compress next frame. 404 Resetting session never fails. 405 - The parameters : changes all parameters back to "default". 406 This removes any reference to any dictionary too. 407 Parameters can only be changed between 2 sessions (i.e. no compression is currently ongoing) 408 otherwise the reset fails, and function returns an error value (which can be tested using ZSTD_isError()) 409 - Both : similar to resetting the session, followed by resetting parameters. 410 411</p></pre><BR> 412 413<pre><b>size_t ZSTD_compress2( ZSTD_CCtx* cctx, 414 void* dst, size_t dstCapacity, 415 const void* src, size_t srcSize); 416</b><p> Behave the same as ZSTD_compressCCtx(), but compression parameters are set using the advanced API. 417 ZSTD_compress2() always starts a new frame. 418 Should cctx hold data from a previously unfinished frame, everything about it is forgotten. 419 - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*() 420 - The function is always blocking, returns when compression is completed. 421 Hint : compression runs faster if `dstCapacity` >= `ZSTD_compressBound(srcSize)`. 422 @return : compressed size written into `dst` (<= `dstCapacity), 423 or an error code if it fails (which can be tested using ZSTD_isError()). 424 425</p></pre><BR> 426 427<a name="Chapter8"></a><h2>Advanced decompression API</h2><pre></pre> 428 429<pre><b>typedef enum { 430 431 ZSTD_d_windowLogMax=100, </b>/* Select a size limit (in power of 2) beyond which<b> 432 * the streaming API will refuse to allocate memory buffer 433 * in order to protect the host from unreasonable memory requirements. 434 * This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode. 435 * By default, a decompression context accepts window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT). 436 * Special: value 0 means "use default maximum windowLog". */ 437 438 </b>/* note : additional experimental parameters are also available<b> 439 * within the experimental section of the API. 440 * At the time of this writing, they include : 441 * ZSTD_c_format 442 * Because they are not stable, it's necessary to define ZSTD_STATIC_LINKING_ONLY to access them. 443 * note : never ever use experimentalParam? names directly 444 */ 445 ZSTD_d_experimentalParam1=1000 446 447} ZSTD_dParameter; 448</b></pre><BR> 449<pre><b>ZSTD_bounds ZSTD_dParam_getBounds(ZSTD_dParameter dParam); 450</b><p> All parameters must belong to an interval with lower and upper bounds, 451 otherwise they will either trigger an error or be automatically clamped. 452 @return : a structure, ZSTD_bounds, which contains 453 - an error status field, which must be tested using ZSTD_isError() 454 - both lower and upper bounds, inclusive 455 456</p></pre><BR> 457 458<pre><b>size_t ZSTD_DCtx_setParameter(ZSTD_DCtx* dctx, ZSTD_dParameter param, int value); 459</b><p> Set one compression parameter, selected by enum ZSTD_dParameter. 460 All parameters have valid bounds. Bounds can be queried using ZSTD_dParam_getBounds(). 461 Providing a value beyond bound will either clamp it, or trigger an error (depending on parameter). 462 Setting a parameter is only possible during frame initialization (before starting decompression). 463 @return : 0, or an error code (which can be tested using ZSTD_isError()). 464 465</p></pre><BR> 466 467<pre><b>size_t ZSTD_DCtx_reset(ZSTD_DCtx* dctx, ZSTD_ResetDirective reset); 468</b><p> Return a DCtx to clean state. 469 Session and parameters can be reset jointly or separately. 470 Parameters can only be reset when no active frame is being decompressed. 471 @return : 0, or an error code, which can be tested with ZSTD_isError() 472 473</p></pre><BR> 474 475<a name="Chapter9"></a><h2>Streaming</h2><pre></pre> 476 477<pre><b>typedef struct ZSTD_inBuffer_s { 478 const void* src; </b>/**< start of input buffer */<b> 479 size_t size; </b>/**< size of input buffer */<b> 480 size_t pos; </b>/**< position where reading stopped. Will be updated. Necessarily 0 <= pos <= size */<b> 481} ZSTD_inBuffer; 482</b></pre><BR> 483<pre><b>typedef struct ZSTD_outBuffer_s { 484 void* dst; </b>/**< start of output buffer */<b> 485 size_t size; </b>/**< size of output buffer */<b> 486 size_t pos; </b>/**< position where writing stopped. Will be updated. Necessarily 0 <= pos <= size */<b> 487} ZSTD_outBuffer; 488</b></pre><BR> 489<a name="Chapter10"></a><h2>Streaming compression - HowTo</h2><pre> 490 A ZSTD_CStream object is required to track streaming operation. 491 Use ZSTD_createCStream() and ZSTD_freeCStream() to create/release resources. 492 ZSTD_CStream objects can be reused multiple times on consecutive compression operations. 493 It is recommended to re-use ZSTD_CStream since it will play nicer with system's memory, by re-using already allocated memory. 494 495 For parallel execution, use one separate ZSTD_CStream per thread. 496 497 note : since v1.3.0, ZSTD_CStream and ZSTD_CCtx are the same thing. 498 499 Parameters are sticky : when starting a new compression on the same context, 500 it will re-use the same sticky parameters as previous compression session. 501 When in doubt, it's recommended to fully initialize the context before usage. 502 Use ZSTD_CCtx_reset() to reset the context and ZSTD_CCtx_setParameter(), 503 ZSTD_CCtx_setPledgedSrcSize(), or ZSTD_CCtx_loadDictionary() and friends to 504 set more specific parameters, the pledged source size, or load a dictionary. 505 506 Use ZSTD_compressStream2() with ZSTD_e_continue as many times as necessary to 507 consume input stream. The function will automatically update both `pos` 508 fields within `input` and `output`. 509 Note that the function may not consume the entire input, for example, because 510 the output buffer is already full, in which case `input.pos < input.size`. 511 The caller must check if input has been entirely consumed. 512 If not, the caller must make some room to receive more compressed data, 513 and then present again remaining input data. 514 note: ZSTD_e_continue is guaranteed to make some forward progress when called, 515 but doesn't guarantee maximal forward progress. This is especially relevant 516 when compressing with multiple threads. The call won't block if it can 517 consume some input, but if it can't it will wait for some, but not all, 518 output to be flushed. 519 @return : provides a minimum amount of data remaining to be flushed from internal buffers 520 or an error code, which can be tested using ZSTD_isError(). 521 522 At any moment, it's possible to flush whatever data might remain stuck within internal buffer, 523 using ZSTD_compressStream2() with ZSTD_e_flush. `output->pos` will be updated. 524 Note that, if `output->size` is too small, a single invocation with ZSTD_e_flush might not be enough (return code > 0). 525 In which case, make some room to receive more compressed data, and call again ZSTD_compressStream2() with ZSTD_e_flush. 526 You must continue calling ZSTD_compressStream2() with ZSTD_e_flush until it returns 0, at which point you can change the 527 operation. 528 note: ZSTD_e_flush will flush as much output as possible, meaning when compressing with multiple threads, it will 529 block until the flush is complete or the output buffer is full. 530 @return : 0 if internal buffers are entirely flushed, 531 >0 if some data still present within internal buffer (the value is minimal estimation of remaining size), 532 or an error code, which can be tested using ZSTD_isError(). 533 534 Calling ZSTD_compressStream2() with ZSTD_e_end instructs to finish a frame. 535 It will perform a flush and write frame epilogue. 536 The epilogue is required for decoders to consider a frame completed. 537 flush operation is the same, and follows same rules as calling ZSTD_compressStream2() with ZSTD_e_flush. 538 You must continue calling ZSTD_compressStream2() with ZSTD_e_end until it returns 0, at which point you are free to 539 start a new frame. 540 note: ZSTD_e_end will flush as much output as possible, meaning when compressing with multiple threads, it will 541 block until the flush is complete or the output buffer is full. 542 @return : 0 if frame fully completed and fully flushed, 543 >0 if some data still present within internal buffer (the value is minimal estimation of remaining size), 544 or an error code, which can be tested using ZSTD_isError(). 545 546 547<BR></pre> 548 549<pre><b>typedef ZSTD_CCtx ZSTD_CStream; </b>/**< CCtx and CStream are now effectively same object (>= v1.3.0) */<b> 550</b></pre><BR> 551<h3>ZSTD_CStream management functions</h3><pre></pre><b><pre>ZSTD_CStream* ZSTD_createCStream(void); 552size_t ZSTD_freeCStream(ZSTD_CStream* zcs); 553</pre></b><BR> 554<h3>Streaming compression functions</h3><pre></pre><b><pre>typedef enum { 555 ZSTD_e_continue=0, </b>/* collect more data, encoder decides when to output compressed result, for optimal compression ratio */<b> 556 ZSTD_e_flush=1, </b>/* flush any data provided so far,<b> 557 * it creates (at least) one new block, that can be decoded immediately on reception; 558 * frame will continue: any future data can still reference previously compressed data, improving compression. 559 * note : multithreaded compression will block to flush as much output as possible. */ 560 ZSTD_e_end=2 </b>/* flush any remaining data _and_ close current frame.<b> 561 * note that frame is only closed after compressed data is fully flushed (return value == 0). 562 * After that point, any additional data starts a new frame. 563 * note : each frame is independent (does not reference any content from previous frame). 564 : note : multithreaded compression will block to flush as much output as possible. */ 565} ZSTD_EndDirective; 566</pre></b><BR> 567<pre><b>size_t ZSTD_compressStream2( ZSTD_CCtx* cctx, 568 ZSTD_outBuffer* output, 569 ZSTD_inBuffer* input, 570 ZSTD_EndDirective endOp); 571</b><p> Behaves about the same as ZSTD_compressStream, with additional control on end directive. 572 - Compression parameters are pushed into CCtx before starting compression, using ZSTD_CCtx_set*() 573 - Compression parameters cannot be changed once compression is started (save a list of exceptions in multi-threading mode) 574 - output->pos must be <= dstCapacity, input->pos must be <= srcSize 575 - output->pos and input->pos will be updated. They are guaranteed to remain below their respective limit. 576 - When nbWorkers==0 (default), function is blocking : it completes its job before returning to caller. 577 - 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, 578 and then immediately returns, just indicating that there is some data remaining to be flushed. 579 The function nonetheless guarantees forward progress : it will return only after it reads or write at least 1+ byte. 580 - 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. 581 - @return provides a minimum amount of data remaining to be flushed from internal buffers 582 or an error code, which can be tested using ZSTD_isError(). 583 if @return != 0, flush is not fully completed, there is still some data left within internal buffers. 584 This is useful for ZSTD_e_flush, since in this case more flushes are necessary to empty all buffers. 585 For ZSTD_e_end, @return == 0 when internal buffers are fully flushed and frame is completed. 586 - after a ZSTD_e_end directive, if internal buffer is not fully flushed (@return != 0), 587 only ZSTD_e_end or ZSTD_e_flush operations are allowed. 588 Before starting a new compression job, or changing compression parameters, 589 it is required to fully flush internal buffers. 590 591</p></pre><BR> 592 593<pre><b>size_t ZSTD_CStreamInSize(void); </b>/**< recommended size for input buffer */<b> 594</b></pre><BR> 595<pre><b>size_t ZSTD_CStreamOutSize(void); </b>/**< recommended size for output buffer. Guarantee to successfully flush at least one complete compressed block in all circumstances. */<b> 596</b></pre><BR> 597<a name="Chapter11"></a><h2>This is a legacy streaming API, and can be replaced by ZSTD_CCtx_reset() and</h2><pre> ZSTD_compressStream2(). It is redundent, but is still fully supported. 598 Advanced parameters and dictionary compression can only be used through the 599 new API. 600<BR></pre> 601 602<a name="Chapter12"></a><h2>Equivalent to:</h2><pre> 603 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 604 ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any) 605 ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel); 606 607<BR></pre> 608 609<a name="Chapter13"></a><h2>Alternative for ZSTD_compressStream2(zcs, output, input, ZSTD_e_continue).</h2><pre> NOTE: The return value is different. ZSTD_compressStream() returns a hint for 610 the next read size (if non-zero and not an error). ZSTD_compressStream2() 611 returns the number of bytes left to flush (if non-zero and not an error). 612 613<BR></pre> 614 615<a name="Chapter14"></a><h2>Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_flush).</h2><pre></pre> 616 617<a name="Chapter15"></a><h2>Equivalent to ZSTD_compressStream2(zcs, output, &emptyInput, ZSTD_e_end).</h2><pre></pre> 618 619<a name="Chapter16"></a><h2>Streaming decompression - HowTo</h2><pre> 620 A ZSTD_DStream object is required to track streaming operations. 621 Use ZSTD_createDStream() and ZSTD_freeDStream() to create/release resources. 622 ZSTD_DStream objects can be re-used multiple times. 623 624 Use ZSTD_initDStream() to start a new decompression operation. 625 @return : recommended first input size 626 Alternatively, use advanced API to set specific properties. 627 628 Use ZSTD_decompressStream() repetitively to consume your input. 629 The function will update both `pos` fields. 630 If `input.pos < input.size`, some input has not been consumed. 631 It's up to the caller to present again remaining data. 632 The function tries to flush all data decoded immediately, respecting output buffer size. 633 If `output.pos < output.size`, decoder has flushed everything it could. 634 But if `output.pos == output.size`, there might be some data left within internal buffers., 635 In which case, call ZSTD_decompressStream() again to flush whatever remains in the buffer. 636 Note : with no additional input provided, amount of data flushed is necessarily <= ZSTD_BLOCKSIZE_MAX. 637 @return : 0 when a frame is completely decoded and fully flushed, 638 or an error code, which can be tested using ZSTD_isError(), 639 or any other value > 0, which means there is still some decoding or flushing to do to complete current frame : 640 the return value is a suggested next input size (just a hint for better latency) 641 that will never request more than the remaining frame size. 642 643<BR></pre> 644 645<pre><b>typedef ZSTD_DCtx ZSTD_DStream; </b>/**< DCtx and DStream are now effectively same object (>= v1.3.0) */<b> 646</b></pre><BR> 647<h3>ZSTD_DStream management functions</h3><pre></pre><b><pre>ZSTD_DStream* ZSTD_createDStream(void); 648size_t ZSTD_freeDStream(ZSTD_DStream* zds); 649</pre></b><BR> 650<h3>Streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_initDStream(ZSTD_DStream* zds); 651size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inBuffer* input); 652</pre></b><BR> 653<pre><b>size_t ZSTD_DStreamInSize(void); </b>/*!< recommended size for input buffer */<b> 654</b></pre><BR> 655<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> 656</b></pre><BR> 657<a name="Chapter17"></a><h2>Simple dictionary API</h2><pre></pre> 658 659<pre><b>size_t ZSTD_compress_usingDict(ZSTD_CCtx* ctx, 660 void* dst, size_t dstCapacity, 661 const void* src, size_t srcSize, 662 const void* dict,size_t dictSize, 663 int compressionLevel); 664</b><p> Compression at an explicit compression level using a Dictionary. 665 A dictionary can be any arbitrary data segment (also called a prefix), 666 or a buffer with specified information (see dictBuilder/zdict.h). 667 Note : This function loads the dictionary, resulting in significant startup delay. 668 It's intended for a dictionary used only once. 669 Note 2 : When `dict == NULL || dictSize < 8` no dictionary is used. 670</p></pre><BR> 671 672<pre><b>size_t ZSTD_decompress_usingDict(ZSTD_DCtx* dctx, 673 void* dst, size_t dstCapacity, 674 const void* src, size_t srcSize, 675 const void* dict,size_t dictSize); 676</b><p> Decompression using a known Dictionary. 677 Dictionary must be identical to the one used during compression. 678 Note : This function loads the dictionary, resulting in significant startup delay. 679 It's intended for a dictionary used only once. 680 Note : When `dict == NULL || dictSize < 8` no dictionary is used. 681</p></pre><BR> 682 683<a name="Chapter18"></a><h2>Bulk processing dictionary API</h2><pre></pre> 684 685<pre><b>ZSTD_CDict* ZSTD_createCDict(const void* dictBuffer, size_t dictSize, 686 int compressionLevel); 687</b><p> When compressing multiple messages / blocks using the same dictionary, it's recommended to load it only once. 688 ZSTD_createCDict() will create a digested dictionary, ready to start future compression operations without startup cost. 689 ZSTD_CDict can be created once and shared by multiple threads concurrently, since its usage is read-only. 690 `dictBuffer` can be released after ZSTD_CDict creation, because its content is copied within CDict. 691 Consider experimental function `ZSTD_createCDict_byReference()` if you prefer to not duplicate `dictBuffer` content. 692 Note : A ZSTD_CDict can be created from an empty dictBuffer, but it is inefficient when used to compress small data. 693</p></pre><BR> 694 695<pre><b>size_t ZSTD_freeCDict(ZSTD_CDict* CDict); 696</b><p> Function frees memory allocated by ZSTD_createCDict(). 697</p></pre><BR> 698 699<pre><b>size_t ZSTD_compress_usingCDict(ZSTD_CCtx* cctx, 700 void* dst, size_t dstCapacity, 701 const void* src, size_t srcSize, 702 const ZSTD_CDict* cdict); 703</b><p> Compression using a digested Dictionary. 704 Recommended when same dictionary is used multiple times. 705 Note : compression level is _decided at dictionary creation time_, 706 and frame parameters are hardcoded (dictID=yes, contentSize=yes, checksum=no) 707</p></pre><BR> 708 709<pre><b>ZSTD_DDict* ZSTD_createDDict(const void* dictBuffer, size_t dictSize); 710</b><p> Create a digested dictionary, ready to start decompression operation without startup delay. 711 dictBuffer can be released after DDict creation, as its content is copied inside DDict. 712</p></pre><BR> 713 714<pre><b>size_t ZSTD_freeDDict(ZSTD_DDict* ddict); 715</b><p> Function frees memory allocated with ZSTD_createDDict() 716</p></pre><BR> 717 718<pre><b>size_t ZSTD_decompress_usingDDict(ZSTD_DCtx* dctx, 719 void* dst, size_t dstCapacity, 720 const void* src, size_t srcSize, 721 const ZSTD_DDict* ddict); 722</b><p> Decompression using a digested Dictionary. 723 Recommended when same dictionary is used multiple times. 724</p></pre><BR> 725 726<a name="Chapter19"></a><h2>Dictionary helper functions</h2><pre></pre> 727 728<pre><b>unsigned ZSTD_getDictID_fromDict(const void* dict, size_t dictSize); 729</b><p> Provides the dictID stored within dictionary. 730 if @return == 0, the dictionary is not conformant with Zstandard specification. 731 It can still be loaded, but as a content-only dictionary. 732</p></pre><BR> 733 734<pre><b>unsigned ZSTD_getDictID_fromDDict(const ZSTD_DDict* ddict); 735</b><p> Provides the dictID of the dictionary loaded into `ddict`. 736 If @return == 0, the dictionary is not conformant to Zstandard specification, or empty. 737 Non-conformant dictionaries can still be loaded, but as content-only dictionaries. 738</p></pre><BR> 739 740<pre><b>unsigned ZSTD_getDictID_fromFrame(const void* src, size_t srcSize); 741</b><p> Provides the dictID required to decompressed the frame stored within `src`. 742 If @return == 0, the dictID could not be decoded. 743 This could for one of the following reasons : 744 - The frame does not require a dictionary to be decoded (most common case). 745 - The frame was built with dictID intentionally removed. Whatever dictionary is necessary is a hidden information. 746 Note : this use case also happens when using a non-conformant dictionary. 747 - `srcSize` is too small, and as a result, the frame header could not be decoded (only possible if `srcSize < ZSTD_FRAMEHEADERSIZE_MAX`). 748 - This is not a Zstandard frame. 749 When identifying the exact failure cause, it's possible to use ZSTD_getFrameHeader(), which will provide a more precise error code. 750</p></pre><BR> 751 752<a name="Chapter20"></a><h2>Advanced dictionary and prefix API</h2><pre> 753 This API allows dictionaries to be used with ZSTD_compress2(), 754 ZSTD_compressStream2(), and ZSTD_decompress(). Dictionaries are sticky, and 755 only reset with the context is reset with ZSTD_reset_parameters or 756 ZSTD_reset_session_and_parameters. Prefixes are single-use. 757<BR></pre> 758 759<pre><b>size_t ZSTD_CCtx_loadDictionary(ZSTD_CCtx* cctx, const void* dict, size_t dictSize); 760</b><p> Create an internal CDict from `dict` buffer. 761 Decompression will have to use same dictionary. 762 @result : 0, or an error code (which can be tested with ZSTD_isError()). 763 Special: Loading a NULL (or 0-size) dictionary invalidates previous dictionary, 764 meaning "return to no-dictionary mode". 765 Note 1 : Dictionary is sticky, it will be used for all future compressed frames. 766 To return to "no-dictionary" situation, load a NULL dictionary (or reset parameters). 767 Note 2 : Loading a dictionary involves building tables. 768 It's also a CPU consuming operation, with non-negligible impact on latency. 769 Tables are dependent on compression parameters, and for this reason, 770 compression parameters can no longer be changed after loading a dictionary. 771 Note 3 :`dict` content will be copied internally. 772 Use experimental ZSTD_CCtx_loadDictionary_byReference() to reference content instead. 773 In such a case, dictionary buffer must outlive its users. 774 Note 4 : Use ZSTD_CCtx_loadDictionary_advanced() 775 to precisely select how dictionary content must be interpreted. 776</p></pre><BR> 777 778<pre><b>size_t ZSTD_CCtx_refCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); 779</b><p> Reference a prepared dictionary, to be used for all next compressed frames. 780 Note that compression parameters are enforced from within CDict, 781 and supersede any compression parameter previously set within CCtx. 782 The parameters ignored are labled as "superseded-by-cdict" in the ZSTD_cParameter enum docs. 783 The ignored parameters will be used again if the CCtx is returned to no-dictionary mode. 784 The dictionary will remain valid for future compressed frames using same CCtx. 785 @result : 0, or an error code (which can be tested with ZSTD_isError()). 786 Special : Referencing a NULL CDict means "return to no-dictionary mode". 787 Note 1 : Currently, only one dictionary can be managed. 788 Referencing a new dictionary effectively "discards" any previous one. 789 Note 2 : CDict is just referenced, its lifetime must outlive its usage within CCtx. 790</p></pre><BR> 791 792<pre><b>size_t ZSTD_CCtx_refPrefix(ZSTD_CCtx* cctx, 793 const void* prefix, size_t prefixSize); 794</b><p> Reference a prefix (single-usage dictionary) for next compressed frame. 795 A prefix is **only used once**. Tables are discarded at end of frame (ZSTD_e_end). 796 Decompression will need same prefix to properly regenerate data. 797 Compressing with a prefix is similar in outcome as performing a diff and compressing it, 798 but performs much faster, especially during decompression (compression speed is tunable with compression level). 799 @result : 0, or an error code (which can be tested with ZSTD_isError()). 800 Special: Adding any prefix (including NULL) invalidates any previous prefix or dictionary 801 Note 1 : Prefix buffer is referenced. It **must** outlive compression. 802 Its content must remain unmodified during compression. 803 Note 2 : If the intention is to diff some large src data blob with some prior version of itself, 804 ensure that the window size is large enough to contain the entire source. 805 See ZSTD_c_windowLog. 806 Note 3 : Referencing a prefix involves building tables, which are dependent on compression parameters. 807 It's a CPU consuming operation, with non-negligible impact on latency. 808 If there is a need to use the same prefix multiple times, consider loadDictionary instead. 809 Note 4 : By default, the prefix is interpreted as raw content (ZSTD_dm_rawContent). 810 Use experimental ZSTD_CCtx_refPrefix_advanced() to alter dictionary interpretation. 811</p></pre><BR> 812 813<pre><b>size_t ZSTD_DCtx_loadDictionary(ZSTD_DCtx* dctx, const void* dict, size_t dictSize); 814</b><p> Create an internal DDict from dict buffer, 815 to be used to decompress next frames. 816 The dictionary remains valid for all future frames, until explicitly invalidated. 817 @result : 0, or an error code (which can be tested with ZSTD_isError()). 818 Special : Adding a NULL (or 0-size) dictionary invalidates any previous dictionary, 819 meaning "return to no-dictionary mode". 820 Note 1 : Loading a dictionary involves building tables, 821 which has a non-negligible impact on CPU usage and latency. 822 It's recommended to "load once, use many times", to amortize the cost 823 Note 2 :`dict` content will be copied internally, so `dict` can be released after loading. 824 Use ZSTD_DCtx_loadDictionary_byReference() to reference dictionary content instead. 825 Note 3 : Use ZSTD_DCtx_loadDictionary_advanced() to take control of 826 how dictionary content is loaded and interpreted. 827 828</p></pre><BR> 829 830<pre><b>size_t ZSTD_DCtx_refDDict(ZSTD_DCtx* dctx, const ZSTD_DDict* ddict); 831</b><p> Reference a prepared dictionary, to be used to decompress next frames. 832 The dictionary remains active for decompression of future frames using same DCtx. 833 @result : 0, or an error code (which can be tested with ZSTD_isError()). 834 Note 1 : Currently, only one dictionary can be managed. 835 Referencing a new dictionary effectively "discards" any previous one. 836 Special: referencing a NULL DDict means "return to no-dictionary mode". 837 Note 2 : DDict is just referenced, its lifetime must outlive its usage from DCtx. 838 839</p></pre><BR> 840 841<pre><b>size_t ZSTD_DCtx_refPrefix(ZSTD_DCtx* dctx, 842 const void* prefix, size_t prefixSize); 843</b><p> Reference a prefix (single-usage dictionary) to decompress next frame. 844 This is the reverse operation of ZSTD_CCtx_refPrefix(), 845 and must use the same prefix as the one used during compression. 846 Prefix is **only used once**. Reference is discarded at end of frame. 847 End of frame is reached when ZSTD_decompressStream() returns 0. 848 @result : 0, or an error code (which can be tested with ZSTD_isError()). 849 Note 1 : Adding any prefix (including NULL) invalidates any previously set prefix or dictionary 850 Note 2 : Prefix buffer is referenced. It **must** outlive decompression. 851 Prefix buffer must remain unmodified up to the end of frame, 852 reached when ZSTD_decompressStream() returns 0. 853 Note 3 : By default, the prefix is treated as raw content (ZSTD_dm_rawContent). 854 Use ZSTD_CCtx_refPrefix_advanced() to alter dictMode (Experimental section) 855 Note 4 : Referencing a raw content prefix has almost no cpu nor memory cost. 856 A full dictionary is more costly, as it requires building tables. 857 858</p></pre><BR> 859 860<pre><b>size_t ZSTD_sizeof_CCtx(const ZSTD_CCtx* cctx); 861size_t ZSTD_sizeof_DCtx(const ZSTD_DCtx* dctx); 862size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs); 863size_t ZSTD_sizeof_DStream(const ZSTD_DStream* zds); 864size_t ZSTD_sizeof_CDict(const ZSTD_CDict* cdict); 865size_t ZSTD_sizeof_DDict(const ZSTD_DDict* ddict); 866</b><p> These functions give the _current_ memory usage of selected object. 867 Note that object memory usage can evolve (increase or decrease) over time. 868</p></pre><BR> 869 870<a name="Chapter21"></a><h2>ADVANCED AND EXPERIMENTAL FUNCTIONS</h2><pre> 871 The definitions in the following section are considered experimental. 872 They are provided for advanced scenarios. 873 They should never be used with a dynamic library, as prototypes may change in the future. 874 Use them only in association with static linking. 875 876<BR></pre> 877 878<a name="Chapter22"></a><h2>experimental API (static linking only)</h2><pre> 879 The following symbols and constants 880 are not planned to join "stable API" status in the near future. 881 They can still change in future versions. 882 Some of them are planned to remain in the static_only section indefinitely. 883 Some of them might be removed in the future (especially when redundant with existing stable functions) 884 885<BR></pre> 886 887<pre><b>typedef struct { 888 unsigned windowLog; </b>/**< largest match distance : larger == more compression, more memory needed during decompression */<b> 889 unsigned chainLog; </b>/**< fully searched segment : larger == more compression, slower, more memory (useless for fast) */<b> 890 unsigned hashLog; </b>/**< dispatch table : larger == faster, more memory */<b> 891 unsigned searchLog; </b>/**< nb of searches : larger == more compression, slower */<b> 892 unsigned minMatch; </b>/**< match length searched : larger == faster decompression, sometimes less compression */<b> 893 unsigned targetLength; </b>/**< acceptable match size for optimal parser (only) : larger == more compression, slower */<b> 894 ZSTD_strategy strategy; </b>/**< see ZSTD_strategy definition above */<b> 895} ZSTD_compressionParameters; 896</b></pre><BR> 897<pre><b>typedef struct { 898 int contentSizeFlag; </b>/**< 1: content size will be in frame header (when known) */<b> 899 int checksumFlag; </b>/**< 1: generate a 32-bits checksum using XXH64 algorithm at end of frame, for error detection */<b> 900 int noDictIDFlag; </b>/**< 1: no dictID will be saved into frame header (dictID is only useful for dictionary compression) */<b> 901} ZSTD_frameParameters; 902</b></pre><BR> 903<pre><b>typedef struct { 904 ZSTD_compressionParameters cParams; 905 ZSTD_frameParameters fParams; 906} ZSTD_parameters; 907</b></pre><BR> 908<pre><b>typedef enum { 909 ZSTD_dct_auto = 0, </b>/* dictionary is "full" when starting with ZSTD_MAGIC_DICTIONARY, otherwise it is "rawContent" */<b> 910 ZSTD_dct_rawContent = 1, </b>/* ensures dictionary is always loaded as rawContent, even if it starts with ZSTD_MAGIC_DICTIONARY */<b> 911 ZSTD_dct_fullDict = 2 </b>/* refuses to load a dictionary if it does not respect Zstandard's specification, starting with ZSTD_MAGIC_DICTIONARY */<b> 912} ZSTD_dictContentType_e; 913</b></pre><BR> 914<pre><b>typedef enum { 915 ZSTD_dlm_byCopy = 0, </b>/**< Copy dictionary content internally */<b> 916 ZSTD_dlm_byRef = 1, </b>/**< Reference dictionary content -- the dictionary buffer must outlive its users. */<b> 917} ZSTD_dictLoadMethod_e; 918</b></pre><BR> 919<pre><b>typedef enum { 920 </b>/* Opened question : should we have a format ZSTD_f_auto ?<b> 921 * Today, it would mean exactly the same as ZSTD_f_zstd1. 922 * But, in the future, should several formats become supported, 923 * on the compression side, it would mean "default format". 924 * On the decompression side, it would mean "automatic format detection", 925 * so that ZSTD_f_zstd1 would mean "accept *only* zstd frames". 926 * Since meaning is a little different, another option could be to define different enums for compression and decompression. 927 * This question could be kept for later, when there are actually multiple formats to support, 928 * but there is also the question of pinning enum values, and pinning value `0` is especially important */ 929 ZSTD_f_zstd1 = 0, </b>/* zstd frame format, specified in zstd_compression_format.md (default) */<b> 930 ZSTD_f_zstd1_magicless = 1, </b>/* Variant of zstd frame format, without initial 4-bytes magic number.<b> 931 * Useful to save 4 bytes per generated frame. 932 * Decoder cannot recognise automatically this format, requiring this instruction. */ 933} ZSTD_format_e; 934</b></pre><BR> 935<pre><b>typedef enum { 936 </b>/* Note: this enum and the behavior it controls are effectively internal<b> 937 * implementation details of the compressor. They are expected to continue 938 * to evolve and should be considered only in the context of extremely 939 * advanced performance tuning. 940 * 941 * Zstd currently supports the use of a CDict in two ways: 942 * 943 * - The contents of the CDict can be copied into the working context. This 944 * means that the compression can search both the dictionary and input 945 * while operating on a single set of internal tables. This makes 946 * the compression faster per-byte of input. However, the initial copy of 947 * the CDict's tables incurs a fixed cost at the beginning of the 948 * compression. For small compressions (< 8 KB), that copy can dominate 949 * the cost of the compression. 950 * 951 * - The CDict's tables can be used in-place. In this model, compression is 952 * slower per input byte, because the compressor has to search two sets of 953 * tables. However, this model incurs no start-up cost (as long as the 954 * working context's tables can be reused). For small inputs, this can be 955 * faster than copying the CDict's tables. 956 * 957 * Zstd has a simple internal heuristic that selects which strategy to use 958 * at the beginning of a compression. However, if experimentation shows that 959 * Zstd is making poor choices, it is possible to override that choice with 960 * this enum. 961 */ 962 ZSTD_dictDefaultAttach = 0, </b>/* Use the default heuristic. */<b> 963 ZSTD_dictForceAttach = 1, </b>/* Never copy the dictionary. */<b> 964 ZSTD_dictForceCopy = 2, </b>/* Always copy the dictionary. */<b> 965} ZSTD_dictAttachPref_e; 966</b></pre><BR> 967<pre><b>typedef enum { 968 ZSTD_lcm_auto = 0, </b>/**< Automatically determine the compression mode based on the compression level.<b> 969 * Negative compression levels will be uncompressed, and positive compression 970 * levels will be compressed. */ 971 ZSTD_lcm_huffman = 1, </b>/**< Always attempt Huffman compression. Uncompressed literals will still be<b> 972 * emitted if Huffman compression is not profitable. */ 973 ZSTD_lcm_uncompressed = 2, </b>/**< Always emit uncompressed literals. */<b> 974} ZSTD_literalCompressionMode_e; 975</b></pre><BR> 976<a name="Chapter23"></a><h2>Frame size functions</h2><pre></pre> 977 978<pre><b>unsigned long long ZSTD_findDecompressedSize(const void* src, size_t srcSize); 979</b><p> `src` should point to the start of a series of ZSTD encoded and/or skippable frames 980 `srcSize` must be the _exact_ size of this series 981 (i.e. there should be a frame boundary at `src + srcSize`) 982 @return : - decompressed size of all data in all successive frames 983 - if the decompressed size cannot be determined: ZSTD_CONTENTSIZE_UNKNOWN 984 - if an error occurred: ZSTD_CONTENTSIZE_ERROR 985 986 note 1 : decompressed size is an optional field, that may not be present, especially in streaming mode. 987 When `return==ZSTD_CONTENTSIZE_UNKNOWN`, data to decompress could be any size. 988 In which case, it's necessary to use streaming mode to decompress data. 989 note 2 : decompressed size is always present when compression is done with ZSTD_compress() 990 note 3 : decompressed size can be very large (64-bits value), 991 potentially larger than what local system can handle as a single memory segment. 992 In which case, it's necessary to use streaming mode to decompress data. 993 note 4 : If source is untrusted, decompressed size could be wrong or intentionally modified. 994 Always ensure result fits within application's authorized limits. 995 Each application can set its own limits. 996 note 5 : ZSTD_findDecompressedSize handles multiple frames, and so it must traverse the input to 997 read each contained frame header. This is fast as most of the data is skipped, 998 however it does mean that all frame data must be present and valid. 999</p></pre><BR> 1000 1001<a name="Chapter24"></a><h2>ZSTD_decompressBound() :</h2><pre> `src` should point to the start of a series of ZSTD encoded and/or skippable frames 1002 `srcSize` must be the _exact_ size of this series 1003 (i.e. there should be a frame boundary at `src + srcSize`) 1004 @return : - upper-bound for the decompressed size of all data in all successive frames 1005 - if an error occured: ZSTD_CONTENTSIZE_ERROR 1006 1007 note 1 : an error can occur if `src` contains an invalid or incorrectly formatted frame. 1008 note 2 : the upper-bound is exact when the decompressed size field is available in every ZSTD encoded frame of `src`. 1009 in this case, `ZSTD_findDecompressedSize` and `ZSTD_decompressBound` return the same value. 1010 note 3 : when the decompressed size field isn't available, the upper-bound for that frame is calculated by: 1011 upper-bound = # blocks * min(128 KB, Window_Size) 1012 1013<BR></pre> 1014 1015<pre><b>size_t ZSTD_frameHeaderSize(const void* src, size_t srcSize); 1016</b><p> srcSize must be >= ZSTD_FRAMEHEADERSIZE_PREFIX. 1017 @return : size of the Frame Header, 1018 or an error code (if srcSize is too small) 1019</p></pre><BR> 1020 1021<a name="Chapter25"></a><h2>Memory management</h2><pre></pre> 1022 1023<pre><b>size_t ZSTD_estimateCCtxSize(int compressionLevel); 1024size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams); 1025size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params); 1026size_t ZSTD_estimateDCtxSize(void); 1027</b><p> These functions make it possible to estimate memory usage 1028 of a future {D,C}Ctx, before its creation. 1029 ZSTD_estimateCCtxSize() will provide a budget large enough for any compression level up to selected one. 1030 It will also consider src size to be arbitrarily "large", which is worst case. 1031 If srcSize is known to always be small, ZSTD_estimateCCtxSize_usingCParams() can provide a tighter estimation. 1032 ZSTD_estimateCCtxSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel. 1033 ZSTD_estimateCCtxSize_usingCCtxParams() can be used in tandem with ZSTD_CCtxParams_setParameter(). Only single-threaded compression is supported. This function will return an error code if ZSTD_c_nbWorkers is >= 1. 1034 Note : CCtx size estimation is only correct for single-threaded compression. 1035</p></pre><BR> 1036 1037<pre><b>size_t ZSTD_estimateCStreamSize(int compressionLevel); 1038size_t ZSTD_estimateCStreamSize_usingCParams(ZSTD_compressionParameters cParams); 1039size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params); 1040size_t ZSTD_estimateDStreamSize(size_t windowSize); 1041size_t ZSTD_estimateDStreamSize_fromFrame(const void* src, size_t srcSize); 1042</b><p> ZSTD_estimateCStreamSize() will provide a budget large enough for any compression level up to selected one. 1043 It will also consider src size to be arbitrarily "large", which is worst case. 1044 If srcSize is known to always be small, ZSTD_estimateCStreamSize_usingCParams() can provide a tighter estimation. 1045 ZSTD_estimateCStreamSize_usingCParams() can be used in tandem with ZSTD_getCParams() to create cParams from compressionLevel. 1046 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. 1047 Note : CStream size estimation is only correct for single-threaded compression. 1048 ZSTD_DStream memory budget depends on window Size. 1049 This information can be passed manually, using ZSTD_estimateDStreamSize, 1050 or deducted from a valid frame Header, using ZSTD_estimateDStreamSize_fromFrame(); 1051 Note : if streaming is init with function ZSTD_init?Stream_usingDict(), 1052 an internal ?Dict will be created, which additional size is not estimated here. 1053 In this case, get total size by adding ZSTD_estimate?DictSize 1054</p></pre><BR> 1055 1056<pre><b>size_t ZSTD_estimateCDictSize(size_t dictSize, int compressionLevel); 1057size_t ZSTD_estimateCDictSize_advanced(size_t dictSize, ZSTD_compressionParameters cParams, ZSTD_dictLoadMethod_e dictLoadMethod); 1058size_t ZSTD_estimateDDictSize(size_t dictSize, ZSTD_dictLoadMethod_e dictLoadMethod); 1059</b><p> ZSTD_estimateCDictSize() will bet that src size is relatively "small", and content is copied, like ZSTD_createCDict(). 1060 ZSTD_estimateCDictSize_advanced() makes it possible to control compression parameters precisely, like ZSTD_createCDict_advanced(). 1061 Note : dictionaries created by reference (`ZSTD_dlm_byRef`) are logically smaller. 1062 1063</p></pre><BR> 1064 1065<pre><b>ZSTD_CCtx* ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize); 1066ZSTD_CStream* ZSTD_initStaticCStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticCCtx() */<b> 1067</b><p> Initialize an object using a pre-allocated fixed-size buffer. 1068 workspace: The memory area to emplace the object into. 1069 Provided pointer *must be 8-bytes aligned*. 1070 Buffer must outlive object. 1071 workspaceSize: Use ZSTD_estimate*Size() to determine 1072 how large workspace must be to support target scenario. 1073 @return : pointer to object (same address as workspace, just different type), 1074 or NULL if error (size too small, incorrect alignment, etc.) 1075 Note : zstd will never resize nor malloc() when using a static buffer. 1076 If the object requires more memory than available, 1077 zstd will just error out (typically ZSTD_error_memory_allocation). 1078 Note 2 : there is no corresponding "free" function. 1079 Since workspace is allocated externally, it must be freed externally too. 1080 Note 3 : cParams : use ZSTD_getCParams() to convert a compression level 1081 into its associated cParams. 1082 Limitation 1 : currently not compatible with internal dictionary creation, triggered by 1083 ZSTD_CCtx_loadDictionary(), ZSTD_initCStream_usingDict() or ZSTD_initDStream_usingDict(). 1084 Limitation 2 : static cctx currently not compatible with multi-threading. 1085 Limitation 3 : static dctx is incompatible with legacy support. 1086 1087</p></pre><BR> 1088 1089<pre><b>ZSTD_DStream* ZSTD_initStaticDStream(void* workspace, size_t workspaceSize); </b>/**< same as ZSTD_initStaticDCtx() */<b> 1090</b></pre><BR> 1091<pre><b>typedef void* (*ZSTD_allocFunction) (void* opaque, size_t size); 1092typedef void (*ZSTD_freeFunction) (void* opaque, void* address); 1093typedef struct { ZSTD_allocFunction customAlloc; ZSTD_freeFunction customFree; void* opaque; } ZSTD_customMem; 1094static ZSTD_customMem const ZSTD_defaultCMem = { NULL, NULL, NULL }; </b>/**< this constant defers to stdlib's functions */<b> 1095</b><p> These prototypes make it possible to pass your own allocation/free functions. 1096 ZSTD_customMem is provided at creation time, using ZSTD_create*_advanced() variants listed below. 1097 All allocation/free operations will be completed using these custom variants instead of regular <stdlib.h> ones. 1098 1099</p></pre><BR> 1100 1101<a name="Chapter26"></a><h2>Advanced compression functions</h2><pre></pre> 1102 1103<pre><b>ZSTD_CDict* ZSTD_createCDict_byReference(const void* dictBuffer, size_t dictSize, int compressionLevel); 1104</b><p> Create a digested dictionary for compression 1105 Dictionary content is just referenced, not duplicated. 1106 As a consequence, `dictBuffer` **must** outlive CDict, 1107 and its content must remain unmodified throughout the lifetime of CDict. 1108</p></pre><BR> 1109 1110<pre><b>ZSTD_compressionParameters ZSTD_getCParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize); 1111</b><p> @return ZSTD_compressionParameters structure for a selected compression level and estimated srcSize. 1112 `estimatedSrcSize` value is optional, select 0 if not known 1113</p></pre><BR> 1114 1115<pre><b>ZSTD_parameters ZSTD_getParams(int compressionLevel, unsigned long long estimatedSrcSize, size_t dictSize); 1116</b><p> same as ZSTD_getCParams(), but @return a full `ZSTD_parameters` object instead of sub-component `ZSTD_compressionParameters`. 1117 All fields of `ZSTD_frameParameters` are set to default : contentSize=1, checksum=0, noDictID=0 1118</p></pre><BR> 1119 1120<pre><b>size_t ZSTD_checkCParams(ZSTD_compressionParameters params); 1121</b><p> Ensure param values remain within authorized range. 1122 @return 0 on success, or an error code (can be checked with ZSTD_isError()) 1123</p></pre><BR> 1124 1125<pre><b>ZSTD_compressionParameters ZSTD_adjustCParams(ZSTD_compressionParameters cPar, unsigned long long srcSize, size_t dictSize); 1126</b><p> optimize params for a given `srcSize` and `dictSize`. 1127 `srcSize` can be unknown, in which case use ZSTD_CONTENTSIZE_UNKNOWN. 1128 `dictSize` must be `0` when there is no dictionary. 1129 cPar can be invalid : all parameters will be clamped within valid range in the @return struct. 1130 This function never fails (wide contract) 1131</p></pre><BR> 1132 1133<pre><b>size_t ZSTD_compress_advanced(ZSTD_CCtx* cctx, 1134 void* dst, size_t dstCapacity, 1135 const void* src, size_t srcSize, 1136 const void* dict,size_t dictSize, 1137 ZSTD_parameters params); 1138</b><p> Same as ZSTD_compress_usingDict(), with fine-tune control over compression parameters (by structure) 1139</p></pre><BR> 1140 1141<pre><b>size_t ZSTD_compress_usingCDict_advanced(ZSTD_CCtx* cctx, 1142 void* dst, size_t dstCapacity, 1143 const void* src, size_t srcSize, 1144 const ZSTD_CDict* cdict, 1145 ZSTD_frameParameters fParams); 1146</b><p> Same as ZSTD_compress_usingCDict(), with fine-tune control over frame parameters 1147</p></pre><BR> 1148 1149<pre><b>size_t ZSTD_CCtx_loadDictionary_byReference(ZSTD_CCtx* cctx, const void* dict, size_t dictSize); 1150</b><p> Same as ZSTD_CCtx_loadDictionary(), but dictionary content is referenced, instead of being copied into CCtx. 1151 It saves some memory, but also requires that `dict` outlives its usage within `cctx` 1152</p></pre><BR> 1153 1154<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); 1155</b><p> Same as ZSTD_CCtx_loadDictionary(), but gives finer control over 1156 how to load the dictionary (by copy ? by reference ?) 1157 and how to interpret it (automatic ? force raw mode ? full mode only ?) 1158</p></pre><BR> 1159 1160<pre><b>size_t ZSTD_CCtx_refPrefix_advanced(ZSTD_CCtx* cctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType); 1161</b><p> Same as ZSTD_CCtx_refPrefix(), but gives finer control over 1162 how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?) 1163</p></pre><BR> 1164 1165<pre><b>size_t ZSTD_CCtx_getParameter(ZSTD_CCtx* cctx, ZSTD_cParameter param, int* value); 1166</b><p> Get the requested compression parameter value, selected by enum ZSTD_cParameter, 1167 and store it into int* value. 1168 @return : 0, or an error code (which can be tested with ZSTD_isError()). 1169 1170</p></pre><BR> 1171 1172<pre><b>ZSTD_CCtx_params* ZSTD_createCCtxParams(void); 1173size_t ZSTD_freeCCtxParams(ZSTD_CCtx_params* params); 1174</b><p> Quick howto : 1175 - ZSTD_createCCtxParams() : Create a ZSTD_CCtx_params structure 1176 - ZSTD_CCtxParams_setParameter() : Push parameters one by one into 1177 an existing ZSTD_CCtx_params structure. 1178 This is similar to 1179 ZSTD_CCtx_setParameter(). 1180 - ZSTD_CCtx_setParametersUsingCCtxParams() : Apply parameters to 1181 an existing CCtx. 1182 These parameters will be applied to 1183 all subsequent frames. 1184 - ZSTD_compressStream2() : Do compression using the CCtx. 1185 - ZSTD_freeCCtxParams() : Free the memory. 1186 1187 This can be used with ZSTD_estimateCCtxSize_advanced_usingCCtxParams() 1188 for static allocation of CCtx for single-threaded compression. 1189 1190</p></pre><BR> 1191 1192<pre><b>size_t ZSTD_CCtxParams_reset(ZSTD_CCtx_params* params); 1193</b><p> Reset params to default values. 1194 1195</p></pre><BR> 1196 1197<pre><b>size_t ZSTD_CCtxParams_init(ZSTD_CCtx_params* cctxParams, int compressionLevel); 1198</b><p> Initializes the compression parameters of cctxParams according to 1199 compression level. All other parameters are reset to their default values. 1200 1201</p></pre><BR> 1202 1203<pre><b>size_t ZSTD_CCtxParams_init_advanced(ZSTD_CCtx_params* cctxParams, ZSTD_parameters params); 1204</b><p> Initializes the compression and frame parameters of cctxParams according to 1205 params. All other parameters are reset to their default values. 1206 1207</p></pre><BR> 1208 1209<pre><b>size_t ZSTD_CCtxParams_setParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int value); 1210</b><p> Similar to ZSTD_CCtx_setParameter. 1211 Set one compression parameter, selected by enum ZSTD_cParameter. 1212 Parameters must be applied to a ZSTD_CCtx using ZSTD_CCtx_setParametersUsingCCtxParams(). 1213 @result : 0, or an error code (which can be tested with ZSTD_isError()). 1214 1215</p></pre><BR> 1216 1217<pre><b>size_t ZSTD_CCtxParams_getParameter(ZSTD_CCtx_params* params, ZSTD_cParameter param, int* value); 1218</b><p> Similar to ZSTD_CCtx_getParameter. 1219 Get the requested value of one compression parameter, selected by enum ZSTD_cParameter. 1220 @result : 0, or an error code (which can be tested with ZSTD_isError()). 1221 1222</p></pre><BR> 1223 1224<pre><b>size_t ZSTD_CCtx_setParametersUsingCCtxParams( 1225 ZSTD_CCtx* cctx, const ZSTD_CCtx_params* params); 1226</b><p> Apply a set of ZSTD_CCtx_params to the compression context. 1227 This can be done even after compression is started, 1228 if nbWorkers==0, this will have no impact until a new compression is started. 1229 if nbWorkers>=1, new parameters will be picked up at next job, 1230 with a few restrictions (windowLog, pledgedSrcSize, nbWorkers, jobSize, and overlapLog are not updated). 1231 1232</p></pre><BR> 1233 1234<pre><b>size_t ZSTD_compressStream2_simpleArgs ( 1235 ZSTD_CCtx* cctx, 1236 void* dst, size_t dstCapacity, size_t* dstPos, 1237 const void* src, size_t srcSize, size_t* srcPos, 1238 ZSTD_EndDirective endOp); 1239</b><p> Same as ZSTD_compressStream2(), 1240 but using only integral types as arguments. 1241 This variant might be helpful for binders from dynamic languages 1242 which have troubles handling structures containing memory pointers. 1243 1244</p></pre><BR> 1245 1246<a name="Chapter27"></a><h2>Advanced decompression functions</h2><pre></pre> 1247 1248<pre><b>unsigned ZSTD_isFrame(const void* buffer, size_t size); 1249</b><p> Tells if the content of `buffer` starts with a valid Frame Identifier. 1250 Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0. 1251 Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled. 1252 Note 3 : Skippable Frame Identifiers are considered valid. 1253</p></pre><BR> 1254 1255<pre><b>ZSTD_DDict* ZSTD_createDDict_byReference(const void* dictBuffer, size_t dictSize); 1256</b><p> Create a digested dictionary, ready to start decompression operation without startup delay. 1257 Dictionary content is referenced, and therefore stays in dictBuffer. 1258 It is important that dictBuffer outlives DDict, 1259 it must remain read accessible throughout the lifetime of DDict 1260</p></pre><BR> 1261 1262<pre><b>size_t ZSTD_DCtx_loadDictionary_byReference(ZSTD_DCtx* dctx, const void* dict, size_t dictSize); 1263</b><p> Same as ZSTD_DCtx_loadDictionary(), 1264 but references `dict` content instead of copying it into `dctx`. 1265 This saves memory if `dict` remains around., 1266 However, it's imperative that `dict` remains accessible (and unmodified) while being used, so it must outlive decompression. 1267</p></pre><BR> 1268 1269<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); 1270</b><p> Same as ZSTD_DCtx_loadDictionary(), 1271 but gives direct control over 1272 how to load the dictionary (by copy ? by reference ?) 1273 and how to interpret it (automatic ? force raw mode ? full mode only ?). 1274</p></pre><BR> 1275 1276<pre><b>size_t ZSTD_DCtx_refPrefix_advanced(ZSTD_DCtx* dctx, const void* prefix, size_t prefixSize, ZSTD_dictContentType_e dictContentType); 1277</b><p> Same as ZSTD_DCtx_refPrefix(), but gives finer control over 1278 how to interpret prefix content (automatic ? force raw mode (default) ? full mode only ?) 1279</p></pre><BR> 1280 1281<pre><b>size_t ZSTD_DCtx_setMaxWindowSize(ZSTD_DCtx* dctx, size_t maxWindowSize); 1282</b><p> Refuses allocating internal buffers for frames requiring a window size larger than provided limit. 1283 This protects a decoder context from reserving too much memory for itself (potential attack scenario). 1284 This parameter is only useful in streaming mode, since no internal buffer is allocated in single-pass mode. 1285 By default, a decompression context accepts all window sizes <= (1 << ZSTD_WINDOWLOG_LIMIT_DEFAULT) 1286 @return : 0, or an error code (which can be tested using ZSTD_isError()). 1287 1288</p></pre><BR> 1289 1290<pre><b>size_t ZSTD_DCtx_setFormat(ZSTD_DCtx* dctx, ZSTD_format_e format); 1291</b><p> Instruct the decoder context about what kind of data to decode next. 1292 This instruction is mandatory to decode data without a fully-formed header, 1293 such ZSTD_f_zstd1_magicless for example. 1294 @return : 0, or an error code (which can be tested using ZSTD_isError()). 1295</p></pre><BR> 1296 1297<pre><b>size_t ZSTD_decompressStream_simpleArgs ( 1298 ZSTD_DCtx* dctx, 1299 void* dst, size_t dstCapacity, size_t* dstPos, 1300 const void* src, size_t srcSize, size_t* srcPos); 1301</b><p> Same as ZSTD_decompressStream(), 1302 but using only integral types as arguments. 1303 This can be helpful for binders from dynamic languages 1304 which have troubles handling structures containing memory pointers. 1305 1306</p></pre><BR> 1307 1308<a name="Chapter28"></a><h2>Advanced streaming functions</h2><pre> Warning : most of these functions are now redundant with the Advanced API. 1309 Once Advanced API reaches "stable" status, 1310 redundant functions will be deprecated, and then at some point removed. 1311<BR></pre> 1312 1313<h3>Advanced Streaming compression functions</h3><pre></pre><b><pre></b>/**! ZSTD_initCStream_srcSize() :<b> 1314 * This function is deprecated, and equivalent to: 1315 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1316 * ZSTD_CCtx_refCDict(zcs, NULL); // clear the dictionary (if any) 1317 * ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel); 1318 * ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1319 * 1320 * pledgedSrcSize must be correct. If it is not known at init time, use 1321 * ZSTD_CONTENTSIZE_UNKNOWN. Note that, for compatibility with older programs, 1322 * "0" also disables frame content size field. It may be enabled in the future. 1323 */ 1324size_t ZSTD_initCStream_srcSize(ZSTD_CStream* zcs, int compressionLevel, unsigned long long pledgedSrcSize); 1325</b>/**! ZSTD_initCStream_usingDict() :<b> 1326 * This function is deprecated, and is equivalent to: 1327 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1328 * ZSTD_CCtx_setParameter(zcs, ZSTD_c_compressionLevel, compressionLevel); 1329 * ZSTD_CCtx_loadDictionary(zcs, dict, dictSize); 1330 * 1331 * Creates of an internal CDict (incompatible with static CCtx), except if 1332 * dict == NULL or dictSize < 8, in which case no dict is used. 1333 * Note: dict is loaded with ZSTD_dm_auto (treated as a full zstd dictionary if 1334 * it begins with ZSTD_MAGIC_DICTIONARY, else as raw content) and ZSTD_dlm_byCopy. 1335 */ 1336size_t ZSTD_initCStream_usingDict(ZSTD_CStream* zcs, const void* dict, size_t dictSize, int compressionLevel); 1337</b>/**! ZSTD_initCStream_advanced() :<b> 1338 * This function is deprecated, and is approximately equivalent to: 1339 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1340 * ZSTD_CCtx_setZstdParams(zcs, params); // Set the zstd params and leave the rest as-is 1341 * ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1342 * ZSTD_CCtx_loadDictionary(zcs, dict, dictSize); 1343 * 1344 * pledgedSrcSize must be correct. If srcSize is not known at init time, use 1345 * value ZSTD_CONTENTSIZE_UNKNOWN. dict is loaded with ZSTD_dm_auto and ZSTD_dlm_byCopy. 1346 */ 1347size_t ZSTD_initCStream_advanced(ZSTD_CStream* zcs, const void* dict, size_t dictSize, 1348 ZSTD_parameters params, unsigned long long pledgedSrcSize); 1349</b>/**! ZSTD_initCStream_usingCDict() :<b> 1350 * This function is deprecated, and equivalent to: 1351 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1352 * ZSTD_CCtx_refCDict(zcs, cdict); 1353 * 1354 * note : cdict will just be referenced, and must outlive compression session 1355 */ 1356size_t ZSTD_initCStream_usingCDict(ZSTD_CStream* zcs, const ZSTD_CDict* cdict); 1357</b>/**! ZSTD_initCStream_usingCDict_advanced() :<b> 1358 * This function is deprecated, and is approximately equivalent to: 1359 * ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1360 * ZSTD_CCtx_setZstdFrameParams(zcs, fParams); // Set the zstd frame params and leave the rest as-is 1361 * ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1362 * ZSTD_CCtx_refCDict(zcs, cdict); 1363 * 1364 * same as ZSTD_initCStream_usingCDict(), with control over frame parameters. 1365 * pledgedSrcSize must be correct. If srcSize is not known at init time, use 1366 * value ZSTD_CONTENTSIZE_UNKNOWN. 1367 */ 1368size_t ZSTD_initCStream_usingCDict_advanced(ZSTD_CStream* zcs, const ZSTD_CDict* cdict, ZSTD_frameParameters fParams, unsigned long long pledgedSrcSize); 1369</pre></b><BR> 1370<pre><b>size_t ZSTD_resetCStream(ZSTD_CStream* zcs, unsigned long long pledgedSrcSize); 1371</b><p> This function is deprecated, and is equivalent to: 1372 ZSTD_CCtx_reset(zcs, ZSTD_reset_session_only); 1373 ZSTD_CCtx_setPledgedSrcSize(zcs, pledgedSrcSize); 1374 1375 start a new frame, using same parameters from previous frame. 1376 This is typically useful to skip dictionary loading stage, since it will re-use it in-place. 1377 Note that zcs must be init at least once before using ZSTD_resetCStream(). 1378 If pledgedSrcSize is not known at reset time, use macro ZSTD_CONTENTSIZE_UNKNOWN. 1379 If pledgedSrcSize > 0, its value must be correct, as it will be written in header, and controlled at the end. 1380 For the time being, pledgedSrcSize==0 is interpreted as "srcSize unknown" for compatibility with older programs, 1381 but it will change to mean "empty" in future version, so use macro ZSTD_CONTENTSIZE_UNKNOWN instead. 1382 @return : 0, or an error code (which can be tested using ZSTD_isError()) 1383 1384</p></pre><BR> 1385 1386<pre><b>typedef struct { 1387 unsigned long long ingested; </b>/* nb input bytes read and buffered */<b> 1388 unsigned long long consumed; </b>/* nb input bytes actually compressed */<b> 1389 unsigned long long produced; </b>/* nb of compressed bytes generated and buffered */<b> 1390 unsigned long long flushed; </b>/* nb of compressed bytes flushed : not provided; can be tracked from caller side */<b> 1391 unsigned currentJobID; </b>/* MT only : latest started job nb */<b> 1392 unsigned nbActiveWorkers; </b>/* MT only : nb of workers actively compressing at probe time */<b> 1393} ZSTD_frameProgression; 1394</b></pre><BR> 1395<pre><b>size_t ZSTD_toFlushNow(ZSTD_CCtx* cctx); 1396</b><p> Tell how many bytes are ready to be flushed immediately. 1397 Useful for multithreading scenarios (nbWorkers >= 1). 1398 Probe the oldest active job, defined as oldest job not yet entirely flushed, 1399 and check its output buffer. 1400 @return : amount of data stored in oldest job and ready to be flushed immediately. 1401 if @return == 0, it means either : 1402 + there is no active job (could be checked with ZSTD_frameProgression()), or 1403 + oldest job is still actively compressing data, 1404 but everything it has produced has also been flushed so far, 1405 therefore flush speed is limited by production speed of oldest job 1406 irrespective of the speed of concurrent (and newer) jobs. 1407 1408</p></pre><BR> 1409 1410<h3>Advanced Streaming decompression functions</h3><pre></pre><b><pre>size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t dictSize); </b>/**< note: no dictionary will be used if dict == NULL or dictSize < 8 */<b> 1411size_t ZSTD_initDStream_usingDDict(ZSTD_DStream* zds, const ZSTD_DDict* ddict); </b>/**< note : ddict is referenced, it must outlive decompression session */<b> 1412size_t ZSTD_resetDStream(ZSTD_DStream* zds); </b>/**< re-use decompression parameters from previous init; saves dictionary loading */<b> 1413</pre></b><BR> 1414<a name="Chapter29"></a><h2>Buffer-less and synchronous inner streaming functions</h2><pre> 1415 This is an advanced API, giving full control over buffer management, for users which need direct control over memory. 1416 But it's also a complex one, with several restrictions, documented below. 1417 Prefer normal streaming API for an easier experience. 1418 1419<BR></pre> 1420 1421<a name="Chapter30"></a><h2>Buffer-less streaming compression (synchronous mode)</h2><pre> 1422 A ZSTD_CCtx object is required to track streaming operations. 1423 Use ZSTD_createCCtx() / ZSTD_freeCCtx() to manage resource. 1424 ZSTD_CCtx object can be re-used multiple times within successive compression operations. 1425 1426 Start by initializing a context. 1427 Use ZSTD_compressBegin(), or ZSTD_compressBegin_usingDict() for dictionary compression, 1428 or ZSTD_compressBegin_advanced(), for finer parameter control. 1429 It's also possible to duplicate a reference context which has already been initialized, using ZSTD_copyCCtx() 1430 1431 Then, consume your input using ZSTD_compressContinue(). 1432 There are some important considerations to keep in mind when using this advanced function : 1433 - ZSTD_compressContinue() has no internal buffer. It uses externally provided buffers only. 1434 - Interface is synchronous : input is consumed entirely and produces 1+ compressed blocks. 1435 - Caller must ensure there is enough space in `dst` to store compressed data under worst case scenario. 1436 Worst case evaluation is provided by ZSTD_compressBound(). 1437 ZSTD_compressContinue() doesn't guarantee recover after a failed compression. 1438 - ZSTD_compressContinue() presumes prior input ***is still accessible and unmodified*** (up to maximum distance size, see WindowLog). 1439 It remembers all previous contiguous blocks, plus one separated memory segment (which can itself consists of multiple contiguous blocks) 1440 - ZSTD_compressContinue() detects that prior input has been overwritten when `src` buffer overlaps. 1441 In which case, it will "discard" the relevant memory section from its history. 1442 1443 Finish a frame with ZSTD_compressEnd(), which will write the last block(s) and optional checksum. 1444 It's possible to use srcSize==0, in which case, it will write a final empty block to end the frame. 1445 Without last block mark, frames are considered unfinished (hence corrupted) by compliant decoders. 1446 1447 `ZSTD_CCtx` object can be re-used (ZSTD_compressBegin()) to compress again. 1448<BR></pre> 1449 1450<h3>Buffer-less streaming compression functions</h3><pre></pre><b><pre>size_t ZSTD_compressBegin(ZSTD_CCtx* cctx, int compressionLevel); 1451size_t ZSTD_compressBegin_usingDict(ZSTD_CCtx* cctx, const void* dict, size_t dictSize, int compressionLevel); 1452size_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> 1453size_t ZSTD_compressBegin_usingCDict(ZSTD_CCtx* cctx, const ZSTD_CDict* cdict); </b>/**< note: fails if cdict==NULL */<b> 1454size_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> 1455size_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> 1456</pre></b><BR> 1457<a name="Chapter31"></a><h2>Buffer-less streaming decompression (synchronous mode)</h2><pre> 1458 A ZSTD_DCtx object is required to track streaming operations. 1459 Use ZSTD_createDCtx() / ZSTD_freeDCtx() to manage it. 1460 A ZSTD_DCtx object can be re-used multiple times. 1461 1462 First typical operation is to retrieve frame parameters, using ZSTD_getFrameHeader(). 1463 Frame header is extracted from the beginning of compressed frame, so providing only the frame's beginning is enough. 1464 Data fragment must be large enough to ensure successful decoding. 1465 `ZSTD_frameHeaderSize_max` bytes is guaranteed to always be large enough. 1466 @result : 0 : successful decoding, the `ZSTD_frameHeader` structure is correctly filled. 1467 >0 : `srcSize` is too small, please provide at least @result bytes on next attempt. 1468 errorCode, which can be tested using ZSTD_isError(). 1469 1470 It fills a ZSTD_frameHeader structure with important information to correctly decode the frame, 1471 such as the dictionary ID, content size, or maximum back-reference distance (`windowSize`). 1472 Note that these values could be wrong, either because of data corruption, or because a 3rd party deliberately spoofs false information. 1473 As a consequence, check that values remain within valid application range. 1474 For example, do not allocate memory blindly, check that `windowSize` is within expectation. 1475 Each application can set its own limits, depending on local restrictions. 1476 For extended interoperability, it is recommended to support `windowSize` of at least 8 MB. 1477 1478 ZSTD_decompressContinue() needs previous data blocks during decompression, up to `windowSize` bytes. 1479 ZSTD_decompressContinue() is very sensitive to contiguity, 1480 if 2 blocks don't follow each other, make sure that either the compressor breaks contiguity at the same place, 1481 or that previous contiguous segment is large enough to properly handle maximum back-reference distance. 1482 There are multiple ways to guarantee this condition. 1483 1484 The most memory efficient way is to use a round buffer of sufficient size. 1485 Sufficient size is determined by invoking ZSTD_decodingBufferSize_min(), 1486 which can @return an error code if required value is too large for current system (in 32-bits mode). 1487 In a round buffer methodology, ZSTD_decompressContinue() decompresses each block next to previous one, 1488 up to the moment there is not enough room left in the buffer to guarantee decoding another full block, 1489 which maximum size is provided in `ZSTD_frameHeader` structure, field `blockSizeMax`. 1490 At which point, decoding can resume from the beginning of the buffer. 1491 Note that already decoded data stored in the buffer should be flushed before being overwritten. 1492 1493 There are alternatives possible, for example using two or more buffers of size `windowSize` each, though they consume more memory. 1494 1495 Finally, if you control the compression process, you can also ignore all buffer size rules, 1496 as long as the encoder and decoder progress in "lock-step", 1497 aka use exactly the same buffer sizes, break contiguity at the same place, etc. 1498 1499 Once buffers are setup, start decompression, with ZSTD_decompressBegin(). 1500 If decompression requires a dictionary, use ZSTD_decompressBegin_usingDict() or ZSTD_decompressBegin_usingDDict(). 1501 1502 Then use ZSTD_nextSrcSizeToDecompress() and ZSTD_decompressContinue() alternatively. 1503 ZSTD_nextSrcSizeToDecompress() tells how many bytes to provide as 'srcSize' to ZSTD_decompressContinue(). 1504 ZSTD_decompressContinue() requires this _exact_ amount of bytes, or it will fail. 1505 1506 @result of ZSTD_decompressContinue() is the number of bytes regenerated within 'dst' (necessarily <= dstCapacity). 1507 It can be zero : it just means ZSTD_decompressContinue() has decoded some metadata item. 1508 It can also be an error code, which can be tested with ZSTD_isError(). 1509 1510 A frame is fully decoded when ZSTD_nextSrcSizeToDecompress() returns zero. 1511 Context can then be reset to start a new decompression. 1512 1513 Note : it's possible to know if next input to present is a header or a block, using ZSTD_nextInputType(). 1514 This information is not required to properly decode a frame. 1515 1516 == Special case : skippable frames 1517 1518 Skippable frames allow integration of user-defined data into a flow of concatenated frames. 1519 Skippable frames will be ignored (skipped) by decompressor. 1520 The format of skippable frames is as follows : 1521 a) Skippable frame ID - 4 Bytes, Little endian format, any value from 0x184D2A50 to 0x184D2A5F 1522 b) Frame Size - 4 Bytes, Little endian format, unsigned 32-bits 1523 c) Frame Content - any content (User Data) of length equal to Frame Size 1524 For skippable frames ZSTD_getFrameHeader() returns zfhPtr->frameType==ZSTD_skippableFrame. 1525 For skippable frames ZSTD_decompressContinue() always returns 0 : it only skips the content. 1526<BR></pre> 1527 1528<h3>Buffer-less streaming decompression functions</h3><pre></pre><b><pre>typedef enum { ZSTD_frame, ZSTD_skippableFrame } ZSTD_frameType_e; 1529typedef struct { 1530 unsigned long long frameContentSize; </b>/* if == ZSTD_CONTENTSIZE_UNKNOWN, it means this field is not available. 0 means "empty" */<b> 1531 unsigned long long windowSize; </b>/* can be very large, up to <= frameContentSize */<b> 1532 unsigned blockSizeMax; 1533 ZSTD_frameType_e frameType; </b>/* if == ZSTD_skippableFrame, frameContentSize is the size of skippable content */<b> 1534 unsigned headerSize; 1535 unsigned dictID; 1536 unsigned checksumFlag; 1537} ZSTD_frameHeader; 1538</pre></b><BR> 1539<a name="Chapter32"></a><h2>ZSTD_getFrameHeader() :</h2><pre> decode Frame Header, or requires larger `srcSize`. 1540 @return : 0, `zfhPtr` is correctly filled, 1541 >0, `srcSize` is too small, value is wanted `srcSize` amount, 1542 or an error code, which can be tested using ZSTD_isError() 1543<BR></pre> 1544 1545<pre><b>size_t ZSTD_getFrameHeader(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize); </b>/**< doesn't consume input */<b> 1546</b></pre><BR> 1547<pre><b>size_t ZSTD_getFrameHeader_advanced(ZSTD_frameHeader* zfhPtr, const void* src, size_t srcSize, ZSTD_format_e format); 1548size_t ZSTD_decodingBufferSize_min(unsigned long long windowSize, unsigned long long frameContentSize); </b>/**< when frame content size is not known, pass in frameContentSize == ZSTD_CONTENTSIZE_UNKNOWN */<b> 1549</b><p> same as ZSTD_getFrameHeader(), 1550 with added capability to select a format (like ZSTD_f_zstd1_magicless) 1551</p></pre><BR> 1552 1553<pre><b>typedef enum { ZSTDnit_frameHeader, ZSTDnit_blockHeader, ZSTDnit_block, ZSTDnit_lastBlock, ZSTDnit_checksum, ZSTDnit_skippableFrame } ZSTD_nextInputType_e; 1554</b></pre><BR> 1555<a name="Chapter33"></a><h2>Block level API</h2><pre></pre> 1556 1557<pre><b></b><p> Frame metadata cost is typically ~18 bytes, which can be non-negligible for very small blocks (< 100 bytes). 1558 User will have to take in charge required information to regenerate data, such as compressed and content sizes. 1559 1560 A few rules to respect : 1561 - Compressing and decompressing require a context structure 1562 + Use ZSTD_createCCtx() and ZSTD_createDCtx() 1563 - It is necessary to init context before starting 1564 + compression : any ZSTD_compressBegin*() variant, including with dictionary 1565 + decompression : any ZSTD_decompressBegin*() variant, including with dictionary 1566 + copyCCtx() and copyDCtx() can be used too 1567 - Block size is limited, it must be <= ZSTD_getBlockSize() <= ZSTD_BLOCKSIZE_MAX == 128 KB 1568 + If input is larger than a block size, it's necessary to split input data into multiple blocks 1569 + For inputs larger than a single block, really consider using regular ZSTD_compress() instead. 1570 Frame metadata is not that costly, and quickly becomes negligible as source size grows larger. 1571 - When a block is considered not compressible enough, ZSTD_compressBlock() result will be zero. 1572 In which case, nothing is produced into `dst` ! 1573 + User must test for such outcome and deal directly with uncompressed data 1574 + ZSTD_decompressBlock() doesn't accept uncompressed data as input !!! 1575 + In case of multiple successive blocks, should some of them be uncompressed, 1576 decoder must be informed of their existence in order to follow proper history. 1577 Use ZSTD_insertBlock() for such a case. 1578</p></pre><BR> 1579 1580<h3>Raw zstd block functions</h3><pre></pre><b><pre>size_t ZSTD_getBlockSize (const ZSTD_CCtx* cctx); 1581size_t ZSTD_compressBlock (ZSTD_CCtx* cctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize); 1582size_t ZSTD_decompressBlock(ZSTD_DCtx* dctx, void* dst, size_t dstCapacity, const void* src, size_t srcSize); 1583size_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> 1584</pre></b><BR> 1585</html> 1586</body> 1587