1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 4<title>1.9.4 Manual</title> 5</head> 6<body> 7<h1>1.9.4 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">Tuning parameter</a></li> 14<li><a href="#Chapter4">Simple Functions</a></li> 15<li><a href="#Chapter5">Advanced Functions</a></li> 16<li><a href="#Chapter6">Streaming Compression Functions</a></li> 17<li><a href="#Chapter7">Streaming Decompression Functions</a></li> 18<li><a href="#Chapter8">Experimental section</a></li> 19<li><a href="#Chapter9">Private Definitions</a></li> 20<li><a href="#Chapter10">Obsolete Functions</a></li> 21</ol> 22<hr> 23<a name="Chapter1"></a><h2>Introduction</h2><pre> 24 LZ4 is lossless compression algorithm, providing compression speed >500 MB/s per core, 25 scalable with multi-cores CPU. It features an extremely fast decoder, with speed in 26 multiple GB/s per core, typically reaching RAM speed limits on multi-core systems. 27 28 The LZ4 compression library provides in-memory compression and decompression functions. 29 It gives full buffer control to user. 30 Compression can be done in: 31 - a single step (described as Simple Functions) 32 - a single step, reusing a context (described in Advanced Functions) 33 - unbounded multiple steps (described as Streaming compression) 34 35 lz4.h generates and decodes LZ4-compressed blocks (doc/lz4_Block_format.md). 36 Decompressing such a compressed block requires additional metadata. 37 Exact metadata depends on exact decompression function. 38 For the typical case of LZ4_decompress_safe(), 39 metadata includes block's compressed size, and maximum bound of decompressed size. 40 Each application is free to encode and pass such metadata in whichever way it wants. 41 42 lz4.h only handle blocks, it can not generate Frames. 43 44 Blocks are different from Frames (doc/lz4_Frame_format.md). 45 Frames bundle both blocks and metadata in a specified manner. 46 Embedding metadata is required for compressed data to be self-contained and portable. 47 Frame format is delivered through a companion API, declared in lz4frame.h. 48 The `lz4` CLI can only manage frames. 49<BR></pre> 50 51<pre><b>#if defined(LZ4_FREESTANDING) && (LZ4_FREESTANDING == 1) 52# define LZ4_HEAPMODE 0 53# define LZ4HC_HEAPMODE 0 54# define LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION 1 55# if !defined(LZ4_memcpy) 56# error "LZ4_FREESTANDING requires macro 'LZ4_memcpy'." 57# endif 58# if !defined(LZ4_memset) 59# error "LZ4_FREESTANDING requires macro 'LZ4_memset'." 60# endif 61# if !defined(LZ4_memmove) 62# error "LZ4_FREESTANDING requires macro 'LZ4_memmove'." 63# endif 64#elif ! defined(LZ4_FREESTANDING) 65# define LZ4_FREESTANDING 0 66#endif 67</b><p> When this macro is set to 1, it enables "freestanding mode" that is 68 suitable for typical freestanding environment which doesn't support 69 standard C library. 70 71 - LZ4_FREESTANDING is a compile-time switch. 72 - It requires the following macros to be defined: 73 LZ4_memcpy, LZ4_memmove, LZ4_memset. 74 - It only enables LZ4/HC functions which don't use heap. 75 All LZ4F_* functions are not supported. 76 - See tests/freestanding.c to check its basic setup. 77 78</p></pre><BR> 79 80<a name="Chapter2"></a><h2>Version</h2><pre></pre> 81 82<pre><b>int LZ4_versionNumber (void); </b>/**< library version number; useful to check dll version; requires v1.3.0+ */<b> 83</b></pre><BR> 84<pre><b>const char* LZ4_versionString (void); </b>/**< library version string; useful to check dll version; requires v1.7.5+ */<b> 85</b></pre><BR> 86<a name="Chapter3"></a><h2>Tuning parameter</h2><pre></pre> 87 88<pre><b>#ifndef LZ4_MEMORY_USAGE 89# define LZ4_MEMORY_USAGE LZ4_MEMORY_USAGE_DEFAULT 90#endif 91</b><p> Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; ) 92 Increasing memory usage improves compression ratio, at the cost of speed. 93 Reduced memory usage may improve speed at the cost of ratio, thanks to better cache locality. 94 Default value is 14, for 16KB, which nicely fits into Intel x86 L1 cache 95 96</p></pre><BR> 97 98<a name="Chapter4"></a><h2>Simple Functions</h2><pre></pre> 99 100<pre><b>int LZ4_compress_default(const char* src, char* dst, int srcSize, int dstCapacity); 101</b><p> Compresses 'srcSize' bytes from buffer 'src' 102 into already allocated 'dst' buffer of size 'dstCapacity'. 103 Compression is guaranteed to succeed if 'dstCapacity' >= LZ4_compressBound(srcSize). 104 It also runs faster, so it's a recommended setting. 105 If the function cannot compress 'src' into a more limited 'dst' budget, 106 compression stops *immediately*, and the function result is zero. 107 In which case, 'dst' content is undefined (invalid). 108 srcSize : max supported value is LZ4_MAX_INPUT_SIZE. 109 dstCapacity : size of buffer 'dst' (which must be already allocated) 110 @return : the number of bytes written into buffer 'dst' (necessarily <= dstCapacity) 111 or 0 if compression fails 112 Note : This function is protected against buffer overflow scenarios (never writes outside 'dst' buffer, nor read outside 'source' buffer). 113 114</p></pre><BR> 115 116<pre><b>int LZ4_decompress_safe (const char* src, char* dst, int compressedSize, int dstCapacity); 117</b><p> compressedSize : is the exact complete size of the compressed block. 118 dstCapacity : is the size of destination buffer (which must be already allocated), presumed an upper bound of decompressed size. 119 @return : the number of bytes decompressed into destination buffer (necessarily <= dstCapacity) 120 If destination buffer is not large enough, decoding will stop and output an error code (negative value). 121 If the source stream is detected malformed, the function will stop decoding and return a negative result. 122 Note 1 : This function is protected against malicious data packets : 123 it will never writes outside 'dst' buffer, nor read outside 'source' buffer, 124 even if the compressed block is maliciously modified to order the decoder to do these actions. 125 In such case, the decoder stops immediately, and considers the compressed block malformed. 126 Note 2 : compressedSize and dstCapacity must be provided to the function, the compressed block does not contain them. 127 The implementation is free to send / store / derive this information in whichever way is most beneficial. 128 If there is a need for a different format which bundles together both compressed data and its metadata, consider looking at lz4frame.h instead. 129 130</p></pre><BR> 131 132<a name="Chapter5"></a><h2>Advanced Functions</h2><pre></pre> 133 134<pre><b>int LZ4_compressBound(int inputSize); 135</b><p> Provides the maximum size that LZ4 compression may output in a "worst case" scenario (input data not compressible) 136 This function is primarily useful for memory allocation purposes (destination buffer size). 137 Macro LZ4_COMPRESSBOUND() is also provided for compilation-time evaluation (stack memory allocation for example). 138 Note that LZ4_compress_default() compresses faster when dstCapacity is >= LZ4_compressBound(srcSize) 139 inputSize : max supported value is LZ4_MAX_INPUT_SIZE 140 return : maximum output size in a "worst case" scenario 141 or 0, if input size is incorrect (too large or negative) 142</p></pre><BR> 143 144<pre><b>int LZ4_compress_fast (const char* src, char* dst, int srcSize, int dstCapacity, int acceleration); 145</b><p> Same as LZ4_compress_default(), but allows selection of "acceleration" factor. 146 The larger the acceleration value, the faster the algorithm, but also the lesser the compression. 147 It's a trade-off. It can be fine tuned, with each successive value providing roughly +~3% to speed. 148 An acceleration value of "1" is the same as regular LZ4_compress_default() 149 Values <= 0 will be replaced by LZ4_ACCELERATION_DEFAULT (currently == 1, see lz4.c). 150 Values > LZ4_ACCELERATION_MAX will be replaced by LZ4_ACCELERATION_MAX (currently == 65537, see lz4.c). 151</p></pre><BR> 152 153<pre><b>int LZ4_sizeofState(void); 154int LZ4_compress_fast_extState (void* state, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration); 155</b><p> Same as LZ4_compress_fast(), using an externally allocated memory space for its state. 156 Use LZ4_sizeofState() to know how much memory must be allocated, 157 and allocate it on 8-bytes boundaries (using `malloc()` typically). 158 Then, provide this buffer as `void* state` to compression function. 159 160</p></pre><BR> 161 162<pre><b>int LZ4_compress_destSize (const char* src, char* dst, int* srcSizePtr, int targetDstSize); 163</b><p> Reverse the logic : compresses as much data as possible from 'src' buffer 164 into already allocated buffer 'dst', of size >= 'targetDestSize'. 165 This function either compresses the entire 'src' content into 'dst' if it's large enough, 166 or fill 'dst' buffer completely with as much data as possible from 'src'. 167 note: acceleration parameter is fixed to "default". 168 169 *srcSizePtr : will be modified to indicate how many bytes where read from 'src' to fill 'dst'. 170 New value is necessarily <= input value. 171 @return : Nb bytes written into 'dst' (necessarily <= targetDestSize) 172 or 0 if compression fails. 173 174 Note : from v1.8.2 to v1.9.1, this function had a bug (fixed un v1.9.2+): 175 the produced compressed content could, in specific circumstances, 176 require to be decompressed into a destination buffer larger 177 by at least 1 byte than the content to decompress. 178 If an application uses `LZ4_compress_destSize()`, 179 it's highly recommended to update liblz4 to v1.9.2 or better. 180 If this can't be done or ensured, 181 the receiving decompression function should provide 182 a dstCapacity which is > decompressedSize, by at least 1 byte. 183 See https://github.com/lz4/lz4/issues/859 for details 184 185</p></pre><BR> 186 187<pre><b>int LZ4_decompress_safe_partial (const char* src, char* dst, int srcSize, int targetOutputSize, int dstCapacity); 188</b><p> Decompress an LZ4 compressed block, of size 'srcSize' at position 'src', 189 into destination buffer 'dst' of size 'dstCapacity'. 190 Up to 'targetOutputSize' bytes will be decoded. 191 The function stops decoding on reaching this objective. 192 This can be useful to boost performance 193 whenever only the beginning of a block is required. 194 195 @return : the number of bytes decoded in `dst` (necessarily <= targetOutputSize) 196 If source stream is detected malformed, function returns a negative result. 197 198 Note 1 : @return can be < targetOutputSize, if compressed block contains less data. 199 200 Note 2 : targetOutputSize must be <= dstCapacity 201 202 Note 3 : this function effectively stops decoding on reaching targetOutputSize, 203 so dstCapacity is kind of redundant. 204 This is because in older versions of this function, 205 decoding operation would still write complete sequences. 206 Therefore, there was no guarantee that it would stop writing at exactly targetOutputSize, 207 it could write more bytes, though only up to dstCapacity. 208 Some "margin" used to be required for this operation to work properly. 209 Thankfully, this is no longer necessary. 210 The function nonetheless keeps the same signature, in an effort to preserve API compatibility. 211 212 Note 4 : If srcSize is the exact size of the block, 213 then targetOutputSize can be any value, 214 including larger than the block's decompressed size. 215 The function will, at most, generate block's decompressed size. 216 217 Note 5 : If srcSize is _larger_ than block's compressed size, 218 then targetOutputSize **MUST** be <= block's decompressed size. 219 Otherwise, *silent corruption will occur*. 220 221</p></pre><BR> 222 223<a name="Chapter6"></a><h2>Streaming Compression Functions</h2><pre></pre> 224 225<pre><b>void LZ4_resetStream_fast (LZ4_stream_t* streamPtr); 226</b><p> Use this to prepare an LZ4_stream_t for a new chain of dependent blocks 227 (e.g., LZ4_compress_fast_continue()). 228 229 An LZ4_stream_t must be initialized once before usage. 230 This is automatically done when created by LZ4_createStream(). 231 However, should the LZ4_stream_t be simply declared on stack (for example), 232 it's necessary to initialize it first, using LZ4_initStream(). 233 234 After init, start any new stream with LZ4_resetStream_fast(). 235 A same LZ4_stream_t can be re-used multiple times consecutively 236 and compress multiple streams, 237 provided that it starts each new stream with LZ4_resetStream_fast(). 238 239 LZ4_resetStream_fast() is much faster than LZ4_initStream(), 240 but is not compatible with memory regions containing garbage data. 241 242 Note: it's only useful to call LZ4_resetStream_fast() 243 in the context of streaming compression. 244 The *extState* functions perform their own resets. 245 Invoking LZ4_resetStream_fast() before is redundant, and even counterproductive. 246 247</p></pre><BR> 248 249<pre><b>int LZ4_loadDict (LZ4_stream_t* streamPtr, const char* dictionary, int dictSize); 250</b><p> Use this function to reference a static dictionary into LZ4_stream_t. 251 The dictionary must remain available during compression. 252 LZ4_loadDict() triggers a reset, so any previous data will be forgotten. 253 The same dictionary will have to be loaded on decompression side for successful decoding. 254 Dictionary are useful for better compression of small data (KB range). 255 While LZ4 accept any input as dictionary, 256 results are generally better when using Zstandard's Dictionary Builder. 257 Loading a size of 0 is allowed, and is the same as reset. 258 @return : loaded dictionary size, in bytes (necessarily <= 64 KB) 259 260</p></pre><BR> 261 262<pre><b>int LZ4_compress_fast_continue (LZ4_stream_t* streamPtr, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration); 263</b><p> Compress 'src' content using data from previously compressed blocks, for better compression ratio. 264 'dst' buffer must be already allocated. 265 If dstCapacity >= LZ4_compressBound(srcSize), compression is guaranteed to succeed, and runs faster. 266 267 @return : size of compressed block 268 or 0 if there is an error (typically, cannot fit into 'dst'). 269 270 Note 1 : Each invocation to LZ4_compress_fast_continue() generates a new block. 271 Each block has precise boundaries. 272 Each block must be decompressed separately, calling LZ4_decompress_*() with relevant metadata. 273 It's not possible to append blocks together and expect a single invocation of LZ4_decompress_*() to decompress them together. 274 275 Note 2 : The previous 64KB of source data is __assumed__ to remain present, unmodified, at same address in memory ! 276 277 Note 3 : When input is structured as a double-buffer, each buffer can have any size, including < 64 KB. 278 Make sure that buffers are separated, by at least one byte. 279 This construction ensures that each block only depends on previous block. 280 281 Note 4 : If input buffer is a ring-buffer, it can have any size, including < 64 KB. 282 283 Note 5 : After an error, the stream status is undefined (invalid), it can only be reset or freed. 284 285</p></pre><BR> 286 287<pre><b>int LZ4_saveDict (LZ4_stream_t* streamPtr, char* safeBuffer, int maxDictSize); 288</b><p> If last 64KB data cannot be guaranteed to remain available at its current memory location, 289 save it into a safer place (char* safeBuffer). 290 This is schematically equivalent to a memcpy() followed by LZ4_loadDict(), 291 but is much faster, because LZ4_saveDict() doesn't need to rebuild tables. 292 @return : saved dictionary size in bytes (necessarily <= maxDictSize), or 0 if error. 293 294</p></pre><BR> 295 296<a name="Chapter7"></a><h2>Streaming Decompression Functions</h2><pre> Bufferless synchronous API 297<BR></pre> 298 299<pre><b>#if !defined(LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION) 300LZ4_streamDecode_t* LZ4_createStreamDecode(void); 301int LZ4_freeStreamDecode (LZ4_streamDecode_t* LZ4_stream); 302#endif </b>/* !defined(LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION) */<b> 303</b><p> creation / destruction of streaming decompression tracking context. 304 A tracking context can be re-used multiple times. 305 306</p></pre><BR> 307 308<pre><b>int LZ4_setStreamDecode (LZ4_streamDecode_t* LZ4_streamDecode, const char* dictionary, int dictSize); 309</b><p> An LZ4_streamDecode_t context can be allocated once and re-used multiple times. 310 Use this function to start decompression of a new stream of blocks. 311 A dictionary can optionally be set. Use NULL or size 0 for a reset order. 312 Dictionary is presumed stable : it must remain accessible and unmodified during next decompression. 313 @return : 1 if OK, 0 if error 314 315</p></pre><BR> 316 317<pre><b>int LZ4_decoderRingBufferSize(int maxBlockSize); 318#define LZ4_DECODER_RING_BUFFER_SIZE(maxBlockSize) (65536 + 14 + (maxBlockSize)) </b>/* for static allocation; maxBlockSize presumed valid */<b> 319</b><p> Note : in a ring buffer scenario (optional), 320 blocks are presumed decompressed next to each other 321 up to the moment there is not enough remaining space for next block (remainingSize < maxBlockSize), 322 at which stage it resumes from beginning of ring buffer. 323 When setting such a ring buffer for streaming decompression, 324 provides the minimum size of this ring buffer 325 to be compatible with any source respecting maxBlockSize condition. 326 @return : minimum ring buffer size, 327 or 0 if there is an error (invalid maxBlockSize). 328 329</p></pre><BR> 330 331<pre><b>int 332LZ4_decompress_safe_continue (LZ4_streamDecode_t* LZ4_streamDecode, 333 const char* src, char* dst, 334 int srcSize, int dstCapacity); 335</b><p> These decoding functions allow decompression of consecutive blocks in "streaming" mode. 336 A block is an unsplittable entity, it must be presented entirely to a decompression function. 337 Decompression functions only accepts one block at a time. 338 The last 64KB of previously decoded data *must* remain available and unmodified at the memory position where they were decoded. 339 If less than 64KB of data has been decoded, all the data must be present. 340 341 Special : if decompression side sets a ring buffer, it must respect one of the following conditions : 342 - Decompression buffer size is _at least_ LZ4_decoderRingBufferSize(maxBlockSize). 343 maxBlockSize is the maximum size of any single block. It can have any value > 16 bytes. 344 In which case, encoding and decoding buffers do not need to be synchronized. 345 Actually, data can be produced by any source compliant with LZ4 format specification, and respecting maxBlockSize. 346 - Synchronized mode : 347 Decompression buffer size is _exactly_ the same as compression buffer size, 348 and follows exactly same update rule (block boundaries at same positions), 349 and decoding function is provided with exact decompressed size of each block (exception for last block of the stream), 350 _then_ decoding & encoding ring buffer can have any size, including small ones ( < 64 KB). 351 - Decompression buffer is larger than encoding buffer, by a minimum of maxBlockSize more bytes. 352 In which case, encoding and decoding buffers do not need to be synchronized, 353 and encoding ring buffer can have any size, including small ones ( < 64 KB). 354 355 Whenever these conditions are not possible, 356 save the last 64KB of decoded data into a safe buffer where it can't be modified during decompression, 357 then indicate where this data is saved using LZ4_setStreamDecode(), before decompressing next block. 358</p></pre><BR> 359 360<pre><b>int 361LZ4_decompress_safe_usingDict(const char* src, char* dst, 362 int srcSize, int dstCapacity, 363 const char* dictStart, int dictSize); 364</b><p> These decoding functions work the same as 365 a combination of LZ4_setStreamDecode() followed by LZ4_decompress_*_continue() 366 They are stand-alone, and don't need an LZ4_streamDecode_t structure. 367 Dictionary is presumed stable : it must remain accessible and unmodified during decompression. 368 Performance tip : Decompression speed can be substantially increased 369 when dst == dictStart + dictSize. 370 371</p></pre><BR> 372 373<a name="Chapter8"></a><h2>Experimental section</h2><pre> 374 Symbols declared in this section must be considered unstable. Their 375 signatures or semantics may change, or they may be removed altogether in the 376 future. They are therefore only safe to depend on when the caller is 377 statically linked against the library. 378 379 To protect against unsafe usage, not only are the declarations guarded, 380 the definitions are hidden by default 381 when building LZ4 as a shared/dynamic library. 382 383 In order to access these declarations, 384 define LZ4_STATIC_LINKING_ONLY in your application 385 before including LZ4's headers. 386 387 In order to make their implementations accessible dynamically, you must 388 define LZ4_PUBLISH_STATIC_FUNCTIONS when building the LZ4 library. 389<BR></pre> 390 391<pre><b>LZ4LIB_STATIC_API int LZ4_compress_fast_extState_fastReset (void* state, const char* src, char* dst, int srcSize, int dstCapacity, int acceleration); 392</b><p> A variant of LZ4_compress_fast_extState(). 393 394 Using this variant avoids an expensive initialization step. 395 It is only safe to call if the state buffer is known to be correctly initialized already 396 (see above comment on LZ4_resetStream_fast() for a definition of "correctly initialized"). 397 From a high level, the difference is that 398 this function initializes the provided state with a call to something like LZ4_resetStream_fast() 399 while LZ4_compress_fast_extState() starts with a call to LZ4_resetStream(). 400 401</p></pre><BR> 402 403<pre><b>LZ4LIB_STATIC_API void 404LZ4_attach_dictionary(LZ4_stream_t* workingStream, 405 const LZ4_stream_t* dictionaryStream); 406</b><p> This is an experimental API that allows 407 efficient use of a static dictionary many times. 408 409 Rather than re-loading the dictionary buffer into a working context before 410 each compression, or copying a pre-loaded dictionary's LZ4_stream_t into a 411 working LZ4_stream_t, this function introduces a no-copy setup mechanism, 412 in which the working stream references the dictionary stream in-place. 413 414 Several assumptions are made about the state of the dictionary stream. 415 Currently, only streams which have been prepared by LZ4_loadDict() should 416 be expected to work. 417 418 Alternatively, the provided dictionaryStream may be NULL, 419 in which case any existing dictionary stream is unset. 420 421 If a dictionary is provided, it replaces any pre-existing stream history. 422 The dictionary contents are the only history that can be referenced and 423 logically immediately precede the data compressed in the first subsequent 424 compression call. 425 426 The dictionary will only remain attached to the working stream through the 427 first compression call, at the end of which it is cleared. The dictionary 428 stream (and source buffer) must remain in-place / accessible / unchanged 429 through the completion of the first compression call on the stream. 430 431</p></pre><BR> 432 433<pre><b></b><p> 434 It's possible to have input and output sharing the same buffer, 435 for highly constrained memory environments. 436 In both cases, it requires input to lay at the end of the buffer, 437 and decompression to start at beginning of the buffer. 438 Buffer size must feature some margin, hence be larger than final size. 439 440 |<------------------------buffer--------------------------------->| 441 |<-----------compressed data--------->| 442 |<-----------decompressed size------------------>| 443 |<----margin---->| 444 445 This technique is more useful for decompression, 446 since decompressed size is typically larger, 447 and margin is short. 448 449 In-place decompression will work inside any buffer 450 which size is >= LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize). 451 This presumes that decompressedSize > compressedSize. 452 Otherwise, it means compression actually expanded data, 453 and it would be more efficient to store such data with a flag indicating it's not compressed. 454 This can happen when data is not compressible (already compressed, or encrypted). 455 456 For in-place compression, margin is larger, as it must be able to cope with both 457 history preservation, requiring input data to remain unmodified up to LZ4_DISTANCE_MAX, 458 and data expansion, which can happen when input is not compressible. 459 As a consequence, buffer size requirements are much higher, 460 and memory savings offered by in-place compression are more limited. 461 462 There are ways to limit this cost for compression : 463 - Reduce history size, by modifying LZ4_DISTANCE_MAX. 464 Note that it is a compile-time constant, so all compressions will apply this limit. 465 Lower values will reduce compression ratio, except when input_size < LZ4_DISTANCE_MAX, 466 so it's a reasonable trick when inputs are known to be small. 467 - Require the compressor to deliver a "maximum compressed size". 468 This is the `dstCapacity` parameter in `LZ4_compress*()`. 469 When this size is < LZ4_COMPRESSBOUND(inputSize), then compression can fail, 470 in which case, the return code will be 0 (zero). 471 The caller must be ready for these cases to happen, 472 and typically design a backup scheme to send data uncompressed. 473 The combination of both techniques can significantly reduce 474 the amount of margin required for in-place compression. 475 476 In-place compression can work in any buffer 477 which size is >= (maxCompressedSize) 478 with maxCompressedSize == LZ4_COMPRESSBOUND(srcSize) for guaranteed compression success. 479 LZ4_COMPRESS_INPLACE_BUFFER_SIZE() depends on both maxCompressedSize and LZ4_DISTANCE_MAX, 480 so it's possible to reduce memory requirements by playing with them. 481 482</p></pre><BR> 483 484<pre><b>#define LZ4_DECOMPRESS_INPLACE_BUFFER_SIZE(decompressedSize) ((decompressedSize) + LZ4_DECOMPRESS_INPLACE_MARGIN(decompressedSize)) </b>/**< note: presumes that compressedSize < decompressedSize. note2: margin is overestimated a bit, since it could use compressedSize instead */<b> 485</b></pre><BR> 486<pre><b>#define LZ4_COMPRESS_INPLACE_BUFFER_SIZE(maxCompressedSize) ((maxCompressedSize) + LZ4_COMPRESS_INPLACE_MARGIN) </b>/**< maxCompressedSize is generally LZ4_COMPRESSBOUND(inputSize), but can be set to any lower value, with the risk that compression can fail (return code 0(zero)) */<b> 487</b></pre><BR> 488<a name="Chapter9"></a><h2>Private Definitions</h2><pre> 489 Do not use these definitions directly. 490 They are only exposed to allow static allocation of `LZ4_stream_t` and `LZ4_streamDecode_t`. 491 Accessing members will expose user code to API and/or ABI break in future versions of the library. 492<BR></pre> 493 494<pre><b></b><p> Never ever use below internal definitions directly ! 495 These definitions are not API/ABI safe, and may change in future versions. 496 If you need static allocation, declare or allocate an LZ4_stream_t object. 497</p></pre><BR> 498 499<pre><b>LZ4_stream_t* LZ4_initStream (void* buffer, size_t size); 500</b><p> An LZ4_stream_t structure must be initialized at least once. 501 This is automatically done when invoking LZ4_createStream(), 502 but it's not when the structure is simply declared on stack (for example). 503 504 Use LZ4_initStream() to properly initialize a newly declared LZ4_stream_t. 505 It can also initialize any arbitrary buffer of sufficient size, 506 and will @return a pointer of proper type upon initialization. 507 508 Note : initialization fails if size and alignment conditions are not respected. 509 In which case, the function will @return NULL. 510 Note2: An LZ4_stream_t structure guarantees correct alignment and size. 511 Note3: Before v1.9.0, use LZ4_resetStream() instead 512</p></pre><BR> 513 514<pre><b>typedef struct { 515 const LZ4_byte* externalDict; 516 const LZ4_byte* prefixEnd; 517 size_t extDictSize; 518 size_t prefixSize; 519} LZ4_streamDecode_t_internal; 520</b><p> Never ever use below internal definitions directly ! 521 These definitions are not API/ABI safe, and may change in future versions. 522 If you need static allocation, declare or allocate an LZ4_streamDecode_t object. 523</p></pre><BR> 524 525<a name="Chapter10"></a><h2>Obsolete Functions</h2><pre></pre> 526 527<pre><b>#ifdef LZ4_DISABLE_DEPRECATE_WARNINGS 528# define LZ4_DEPRECATED(message) </b>/* disable deprecation warnings */<b> 529#else 530# if defined (__cplusplus) && (__cplusplus >= 201402) </b>/* C++14 or greater */<b> 531# define LZ4_DEPRECATED(message) [[deprecated(message)]] 532# elif defined(_MSC_VER) 533# define LZ4_DEPRECATED(message) __declspec(deprecated(message)) 534# elif defined(__clang__) || (defined(__GNUC__) && (__GNUC__ * 10 + __GNUC_MINOR__ >= 45)) 535# define LZ4_DEPRECATED(message) __attribute__((deprecated(message))) 536# elif defined(__GNUC__) && (__GNUC__ * 10 + __GNUC_MINOR__ >= 31) 537# define LZ4_DEPRECATED(message) __attribute__((deprecated)) 538# else 539# pragma message("WARNING: LZ4_DEPRECATED needs custom implementation for this compiler") 540# define LZ4_DEPRECATED(message) </b>/* disabled */<b> 541# endif 542#endif </b>/* LZ4_DISABLE_DEPRECATE_WARNINGS */<b> 543</b><p> 544 Deprecated functions make the compiler generate a warning when invoked. 545 This is meant to invite users to update their source code. 546 Should deprecation warnings be a problem, it is generally possible to disable them, 547 typically with -Wno-deprecated-declarations for gcc 548 or _CRT_SECURE_NO_WARNINGS in Visual. 549 550 Another method is to define LZ4_DISABLE_DEPRECATE_WARNINGS 551 before including the header file. 552 553</p></pre><BR> 554 555<pre><b>LZ4_DEPRECATED("use LZ4_compress_default() instead") LZ4LIB_API int LZ4_compress (const char* src, char* dest, int srcSize); 556LZ4_DEPRECATED("use LZ4_compress_default() instead") LZ4LIB_API int LZ4_compress_limitedOutput (const char* src, char* dest, int srcSize, int maxOutputSize); 557LZ4_DEPRECATED("use LZ4_compress_fast_extState() instead") LZ4LIB_API int LZ4_compress_withState (void* state, const char* source, char* dest, int inputSize); 558LZ4_DEPRECATED("use LZ4_compress_fast_extState() instead") LZ4LIB_API int LZ4_compress_limitedOutput_withState (void* state, const char* source, char* dest, int inputSize, int maxOutputSize); 559LZ4_DEPRECATED("use LZ4_compress_fast_continue() instead") LZ4LIB_API int LZ4_compress_continue (LZ4_stream_t* LZ4_streamPtr, const char* source, char* dest, int inputSize); 560LZ4_DEPRECATED("use LZ4_compress_fast_continue() instead") LZ4LIB_API int LZ4_compress_limitedOutput_continue (LZ4_stream_t* LZ4_streamPtr, const char* source, char* dest, int inputSize, int maxOutputSize); 561</b><p></p></pre><BR> 562 563<pre><b>LZ4_DEPRECATED("use LZ4_decompress_fast() instead") LZ4LIB_API int LZ4_uncompress (const char* source, char* dest, int outputSize); 564LZ4_DEPRECATED("use LZ4_decompress_safe() instead") LZ4LIB_API int LZ4_uncompress_unknownOutputSize (const char* source, char* dest, int isize, int maxOutputSize); 565</b><p></p></pre><BR> 566 567<pre><b>LZ4_DEPRECATED("use LZ4_decompress_safe_usingDict() instead") LZ4LIB_API int LZ4_decompress_safe_withPrefix64k (const char* src, char* dst, int compressedSize, int maxDstSize); 568LZ4_DEPRECATED("use LZ4_decompress_fast_usingDict() instead") LZ4LIB_API int LZ4_decompress_fast_withPrefix64k (const char* src, char* dst, int originalSize); 569</b><p></p></pre><BR> 570 571<pre><b>LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe() instead") 572int LZ4_decompress_fast (const char* src, char* dst, int originalSize); 573LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_continue() instead") 574int LZ4_decompress_fast_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* src, char* dst, int originalSize); 575LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_usingDict() instead") 576int LZ4_decompress_fast_usingDict (const char* src, char* dst, int originalSize, const char* dictStart, int dictSize); 577</b><p> These functions used to be faster than LZ4_decompress_safe(), 578 but this is no longer the case. They are now slower. 579 This is because LZ4_decompress_fast() doesn't know the input size, 580 and therefore must progress more cautiously into the input buffer to not read beyond the end of block. 581 On top of that `LZ4_decompress_fast()` is not protected vs malformed or malicious inputs, making it a security liability. 582 As a consequence, LZ4_decompress_fast() is strongly discouraged, and deprecated. 583 584 The last remaining LZ4_decompress_fast() specificity is that 585 it can decompress a block without knowing its compressed size. 586 Such functionality can be achieved in a more secure manner 587 by employing LZ4_decompress_safe_partial(). 588 589 Parameters: 590 originalSize : is the uncompressed size to regenerate. 591 `dst` must be already allocated, its size must be >= 'originalSize' bytes. 592 @return : number of bytes read from source buffer (== compressed size). 593 The function expects to finish at block's end exactly. 594 If the source stream is detected malformed, the function stops decoding and returns a negative result. 595 note : LZ4_decompress_fast*() requires originalSize. Thanks to this information, it never writes past the output buffer. 596 However, since it doesn't know its 'src' size, it may read an unknown amount of input, past input buffer bounds. 597 Also, since match offsets are not validated, match reads from 'src' may underflow too. 598 These issues never happen if input (compressed) data is correct. 599 But they may happen if input data is invalid (error or intentional tampering). 600 As a consequence, use these functions in trusted environments with trusted data **only**. 601 602</p></pre><BR> 603 604<pre><b>void LZ4_resetStream (LZ4_stream_t* streamPtr); 605</b><p> An LZ4_stream_t structure must be initialized at least once. 606 This is done with LZ4_initStream(), or LZ4_resetStream(). 607 Consider switching to LZ4_initStream(), 608 invoking LZ4_resetStream() will trigger deprecation warnings in the future. 609 610</p></pre><BR> 611 612</html> 613</body> 614