1 /* ******************************************************************
2 * FSE : Finite State Entropy codec
3 * Public Prototypes declaration
4 * Copyright (c) Yann Collet, Facebook, Inc.
6 * You can contact the author at :
7 * - Source repository : https://github.com/Cyan4973/FiniteStateEntropy
9 * This source code is licensed under both the BSD-style license (found in the
10 * LICENSE file in the root directory of this source tree) and the GPLv2 (found
11 * in the COPYING file in the root directory of this source tree).
12 * You may select, at your option, one of the above-listed licenses.
13 ****************************************************************** */
18 /*-*****************************************
20 ******************************************/
21 #include "zstd_deps.h" /* size_t, ptrdiff_t */
23 /*-*****************************************
24 * FSE_PUBLIC_API : control library symbols visibility
25 ******************************************/
26 #if defined(FSE_DLL_EXPORT) && (FSE_DLL_EXPORT==1) && defined(__GNUC__) && (__GNUC__ >= 4)
27 # define FSE_PUBLIC_API __attribute__ ((visibility ("default")))
28 #elif defined(FSE_DLL_EXPORT) && (FSE_DLL_EXPORT==1) /* Visual expected */
29 # define FSE_PUBLIC_API __declspec(dllexport)
30 #elif defined(FSE_DLL_IMPORT) && (FSE_DLL_IMPORT==1)
31 # define FSE_PUBLIC_API __declspec(dllimport) /* It isn't required but allows to generate better code, saving a function pointer load from the IAT and an indirect jump.*/
33 # define FSE_PUBLIC_API
36 /*------ Version ------*/
37 #define FSE_VERSION_MAJOR 0
38 #define FSE_VERSION_MINOR 9
39 #define FSE_VERSION_RELEASE 0
41 #define FSE_LIB_VERSION FSE_VERSION_MAJOR.FSE_VERSION_MINOR.FSE_VERSION_RELEASE
42 #define FSE_QUOTE(str) #str
43 #define FSE_EXPAND_AND_QUOTE(str) FSE_QUOTE(str)
44 #define FSE_VERSION_STRING FSE_EXPAND_AND_QUOTE(FSE_LIB_VERSION)
46 #define FSE_VERSION_NUMBER (FSE_VERSION_MAJOR *100*100 + FSE_VERSION_MINOR *100 + FSE_VERSION_RELEASE)
47 FSE_PUBLIC_API unsigned FSE_versionNumber(void); /*< library version number; to be used when checking dll version */
49 /*-****************************************
50 * FSE simple functions
51 ******************************************/
53 Compress content of buffer 'src', of size 'srcSize', into destination buffer 'dst'.
54 'dst' buffer must be already allocated. Compression runs faster is dstCapacity >= FSE_compressBound(srcSize).
55 @return : size of compressed data (<= dstCapacity).
56 Special values : if return == 0, srcData is not compressible => Nothing is stored within dst !!!
57 if return == 1, srcData is a single byte symbol * srcSize times. Use RLE compression instead.
58 if FSE_isError(return), compression failed (more details using FSE_getErrorName())
60 FSE_PUBLIC_API size_t FSE_compress(void* dst, size_t dstCapacity,
61 const void* src, size_t srcSize);
64 Decompress FSE data from buffer 'cSrc', of size 'cSrcSize',
65 into already allocated destination buffer 'dst', of size 'dstCapacity'.
66 @return : size of regenerated data (<= maxDstSize),
67 or an error code, which can be tested using FSE_isError() .
69 ** Important ** : FSE_decompress() does not decompress non-compressible nor RLE data !!!
70 Why ? : making this distinction requires a header.
71 Header management is intentionally delegated to the user layer, which can better manage special cases.
73 FSE_PUBLIC_API size_t FSE_decompress(void* dst, size_t dstCapacity,
74 const void* cSrc, size_t cSrcSize);
76 /*-*****************************************
78 ******************************************/
79 FSE_PUBLIC_API size_t FSE_compressBound(size_t size); /* maximum compressed size */
81 /* Error Management */
82 FSE_PUBLIC_API unsigned FSE_isError(size_t code); /* tells if a return value is an error code */
83 FSE_PUBLIC_API const char* FSE_getErrorName(size_t code); /* provides error code string (useful for debugging) */
85 /*-*****************************************
86 * FSE advanced functions
87 ******************************************/
89 Same as FSE_compress(), but allows the selection of 'maxSymbolValue' and 'tableLog'
90 Both parameters can be defined as '0' to mean : use default value
91 @return : size of compressed data
92 Special values : if return == 0, srcData is not compressible => Nothing is stored within cSrc !!!
93 if return == 1, srcData is a single byte symbol * srcSize times. Use RLE compression.
94 if FSE_isError(return), it's an error code.
96 FSE_PUBLIC_API size_t FSE_compress2 (void* dst, size_t dstSize, const void* src, size_t srcSize, unsigned maxSymbolValue, unsigned tableLog);
98 /*-*****************************************
100 ******************************************/
102 FSE_compress() does the following:
103 1. count symbol occurrence from source[] into table count[] (see hist.h)
104 2. normalize counters so that sum(count[]) == Power_of_2 (2^tableLog)
105 3. save normalized counters to memory buffer using writeNCount()
106 4. build encoding table 'CTable' from normalized counters
107 5. encode the data stream using encoding table 'CTable'
109 FSE_decompress() does the following:
110 1. read normalized counters with readNCount()
111 2. build decoding table 'DTable' from normalized counters
112 3. decode the data stream using decoding table 'DTable'
114 The following API allows targeting specific sub-functions for advanced tasks.
115 For example, it's possible to compress several blocks using the same 'CTable',
116 or to save and provide normalized distribution using external method.
119 /* *** COMPRESSION *** */
121 /*! FSE_optimalTableLog():
122 dynamically downsize 'tableLog' when conditions are met.
123 It saves CPU time, by using smaller tables, while preserving or even improving compression ratio.
124 @return : recommended tableLog (necessarily <= 'maxTableLog') */
125 FSE_PUBLIC_API unsigned FSE_optimalTableLog(unsigned maxTableLog, size_t srcSize, unsigned maxSymbolValue);
127 /*! FSE_normalizeCount():
128 normalize counts so that sum(count[]) == Power_of_2 (2^tableLog)
129 'normalizedCounter' is a table of short, of minimum size (maxSymbolValue+1).
130 useLowProbCount is a boolean parameter which trades off compressed size for
131 faster header decoding. When it is set to 1, the compressed data will be slightly
132 smaller. And when it is set to 0, FSE_readNCount() and FSE_buildDTable() will be
133 faster. If you are compressing a small amount of data (< 2 KB) then useLowProbCount=0
134 is a good default, since header deserialization makes a big speed difference.
135 Otherwise, useLowProbCount=1 is a good default, since the speed difference is small.
137 or an errorCode, which can be tested using FSE_isError() */
138 FSE_PUBLIC_API size_t FSE_normalizeCount(short* normalizedCounter, unsigned tableLog,
139 const unsigned* count, size_t srcSize, unsigned maxSymbolValue, unsigned useLowProbCount);
141 /*! FSE_NCountWriteBound():
142 Provides the maximum possible size of an FSE normalized table, given 'maxSymbolValue' and 'tableLog'.
143 Typically useful for allocation purpose. */
144 FSE_PUBLIC_API size_t FSE_NCountWriteBound(unsigned maxSymbolValue, unsigned tableLog);
146 /*! FSE_writeNCount():
147 Compactly save 'normalizedCounter' into 'buffer'.
148 @return : size of the compressed table,
149 or an errorCode, which can be tested using FSE_isError(). */
150 FSE_PUBLIC_API size_t FSE_writeNCount (void* buffer, size_t bufferSize,
151 const short* normalizedCounter,
152 unsigned maxSymbolValue, unsigned tableLog);
154 /*! Constructor and Destructor of FSE_CTable.
155 Note that FSE_CTable size depends on 'tableLog' and 'maxSymbolValue' */
156 typedef unsigned FSE_CTable; /* don't allocate that. It's only meant to be more restrictive than void* */
157 FSE_PUBLIC_API FSE_CTable* FSE_createCTable (unsigned maxSymbolValue, unsigned tableLog);
158 FSE_PUBLIC_API void FSE_freeCTable (FSE_CTable* ct);
160 /*! FSE_buildCTable():
161 Builds `ct`, which must be already allocated, using FSE_createCTable().
162 @return : 0, or an errorCode, which can be tested using FSE_isError() */
163 FSE_PUBLIC_API size_t FSE_buildCTable(FSE_CTable* ct, const short* normalizedCounter, unsigned maxSymbolValue, unsigned tableLog);
165 /*! FSE_compress_usingCTable():
166 Compress `src` using `ct` into `dst` which must be already allocated.
167 @return : size of compressed data (<= `dstCapacity`),
168 or 0 if compressed data could not fit into `dst`,
169 or an errorCode, which can be tested using FSE_isError() */
170 FSE_PUBLIC_API size_t FSE_compress_usingCTable (void* dst, size_t dstCapacity, const void* src, size_t srcSize, const FSE_CTable* ct);
175 The first step is to count all symbols. FSE_count() does this job very fast.
176 Result will be saved into 'count', a table of unsigned int, which must be already allocated, and have 'maxSymbolValuePtr[0]+1' cells.
177 'src' is a table of bytes of size 'srcSize'. All values within 'src' MUST be <= maxSymbolValuePtr[0]
178 maxSymbolValuePtr[0] will be updated, with its real value (necessarily <= original value)
179 FSE_count() will return the number of occurrence of the most frequent symbol.
180 This can be used to know if there is a single symbol within 'src', and to quickly evaluate its compressibility.
181 If there is an error, the function will return an ErrorCode (which can be tested using FSE_isError()).
183 The next step is to normalize the frequencies.
184 FSE_normalizeCount() will ensure that sum of frequencies is == 2 ^'tableLog'.
185 It also guarantees a minimum of 1 to any Symbol with frequency >= 1.
186 You can use 'tableLog'==0 to mean "use default tableLog value".
187 If you are unsure of which tableLog value to use, you can ask FSE_optimalTableLog(),
188 which will provide the optimal valid tableLog given sourceSize, maxSymbolValue, and a user-defined maximum (0 means "default").
190 The result of FSE_normalizeCount() will be saved into a table,
191 called 'normalizedCounter', which is a table of signed short.
192 'normalizedCounter' must be already allocated, and have at least 'maxSymbolValue+1' cells.
193 The return value is tableLog if everything proceeded as expected.
194 It is 0 if there is a single symbol within distribution.
195 If there is an error (ex: invalid tableLog value), the function will return an ErrorCode (which can be tested using FSE_isError()).
197 'normalizedCounter' can be saved in a compact manner to a memory area using FSE_writeNCount().
198 'buffer' must be already allocated.
199 For guaranteed success, buffer size must be at least FSE_headerBound().
200 The result of the function is the number of bytes written into 'buffer'.
201 If there is an error, the function will return an ErrorCode (which can be tested using FSE_isError(); ex : buffer size too small).
203 'normalizedCounter' can then be used to create the compression table 'CTable'.
204 The space required by 'CTable' must be already allocated, using FSE_createCTable().
205 You can then use FSE_buildCTable() to fill 'CTable'.
206 If there is an error, both functions will return an ErrorCode (which can be tested using FSE_isError()).
208 'CTable' can then be used to compress 'src', with FSE_compress_usingCTable().
209 Similar to FSE_count(), the convention is that 'src' is assumed to be a table of char of size 'srcSize'
210 The function returns the size of compressed data (without header), necessarily <= `dstCapacity`.
211 If it returns '0', compressed data could not fit into 'dst'.
212 If there is an error, the function will return an ErrorCode (which can be tested using FSE_isError()).
215 /* *** DECOMPRESSION *** */
217 /*! FSE_readNCount():
218 Read compactly saved 'normalizedCounter' from 'rBuffer'.
219 @return : size read from 'rBuffer',
220 or an errorCode, which can be tested using FSE_isError().
221 maxSymbolValuePtr[0] and tableLogPtr[0] will also be updated with their respective values */
222 FSE_PUBLIC_API size_t FSE_readNCount (short* normalizedCounter,
223 unsigned* maxSymbolValuePtr, unsigned* tableLogPtr,
224 const void* rBuffer, size_t rBuffSize);
226 /*! FSE_readNCount_bmi2():
227 * Same as FSE_readNCount() but pass bmi2=1 when your CPU supports BMI2 and 0 otherwise.
229 FSE_PUBLIC_API size_t FSE_readNCount_bmi2(short* normalizedCounter,
230 unsigned* maxSymbolValuePtr, unsigned* tableLogPtr,
231 const void* rBuffer, size_t rBuffSize, int bmi2);
233 /*! Constructor and Destructor of FSE_DTable.
234 Note that its size depends on 'tableLog' */
235 typedef unsigned FSE_DTable; /* don't allocate that. It's just a way to be more restrictive than void* */
236 FSE_PUBLIC_API FSE_DTable* FSE_createDTable(unsigned tableLog);
237 FSE_PUBLIC_API void FSE_freeDTable(FSE_DTable* dt);
239 /*! FSE_buildDTable():
240 Builds 'dt', which must be already allocated, using FSE_createDTable().
241 return : 0, or an errorCode, which can be tested using FSE_isError() */
242 FSE_PUBLIC_API size_t FSE_buildDTable (FSE_DTable* dt, const short* normalizedCounter, unsigned maxSymbolValue, unsigned tableLog);
244 /*! FSE_decompress_usingDTable():
245 Decompress compressed source `cSrc` of size `cSrcSize` using `dt`
246 into `dst` which must be already allocated.
247 @return : size of regenerated data (necessarily <= `dstCapacity`),
248 or an errorCode, which can be tested using FSE_isError() */
249 FSE_PUBLIC_API size_t FSE_decompress_usingDTable(void* dst, size_t dstCapacity, const void* cSrc, size_t cSrcSize, const FSE_DTable* dt);
254 (Note : these functions only decompress FSE-compressed blocks.
255 If block is uncompressed, use memcpy() instead
256 If block is a single repeated byte, use memset() instead )
258 The first step is to obtain the normalized frequencies of symbols.
259 This can be performed by FSE_readNCount() if it was saved using FSE_writeNCount().
260 'normalizedCounter' must be already allocated, and have at least 'maxSymbolValuePtr[0]+1' cells of signed short.
261 In practice, that means it's necessary to know 'maxSymbolValue' beforehand,
262 or size the table to handle worst case situations (typically 256).
263 FSE_readNCount() will provide 'tableLog' and 'maxSymbolValue'.
264 The result of FSE_readNCount() is the number of bytes read from 'rBuffer'.
265 Note that 'rBufferSize' must be at least 4 bytes, even if useful information is less than that.
266 If there is an error, the function will return an error code, which can be tested using FSE_isError().
268 The next step is to build the decompression tables 'FSE_DTable' from 'normalizedCounter'.
269 This is performed by the function FSE_buildDTable().
270 The space required by 'FSE_DTable' must be already allocated using FSE_createDTable().
271 If there is an error, the function will return an error code, which can be tested using FSE_isError().
273 `FSE_DTable` can then be used to decompress `cSrc`, with FSE_decompress_usingDTable().
274 `cSrcSize` must be strictly correct, otherwise decompression will fail.
275 FSE_decompress_usingDTable() result will tell how many bytes were regenerated (<=`dstCapacity`).
276 If there is an error, the function will return an error code, which can be tested using FSE_isError(). (ex: dst buffer too small)
281 #if !defined(FSE_H_FSE_STATIC_LINKING_ONLY)
282 #define FSE_H_FSE_STATIC_LINKING_ONLY
284 /* *** Dependency *** */
285 #include "bitstream.h"
287 /* *****************************************
289 *******************************************/
290 /* FSE buffer bounds */
291 #define FSE_NCOUNTBOUND 512
292 #define FSE_BLOCKBOUND(size) ((size) + ((size)>>7) + 4 /* fse states */ + sizeof(size_t) /* bitContainer */)
293 #define FSE_COMPRESSBOUND(size) (FSE_NCOUNTBOUND + FSE_BLOCKBOUND(size)) /* Macro version, useful for static allocation */
295 /* It is possible to statically allocate FSE CTable/DTable as a table of FSE_CTable/FSE_DTable using below macros */
296 #define FSE_CTABLE_SIZE_U32(maxTableLog, maxSymbolValue) (1 + (1<<((maxTableLog)-1)) + (((maxSymbolValue)+1)*2))
297 #define FSE_DTABLE_SIZE_U32(maxTableLog) (1 + (1<<(maxTableLog)))
299 /* or use the size to malloc() space directly. Pay attention to alignment restrictions though */
300 #define FSE_CTABLE_SIZE(maxTableLog, maxSymbolValue) (FSE_CTABLE_SIZE_U32(maxTableLog, maxSymbolValue) * sizeof(FSE_CTable))
301 #define FSE_DTABLE_SIZE(maxTableLog) (FSE_DTABLE_SIZE_U32(maxTableLog) * sizeof(FSE_DTable))
303 /* *****************************************
305 ***************************************** */
307 unsigned FSE_optimalTableLog_internal(unsigned maxTableLog, size_t srcSize, unsigned maxSymbolValue, unsigned minus);
308 /*< same as FSE_optimalTableLog(), which used `minus==2` */
310 /* FSE_compress_wksp() :
311 * Same as FSE_compress2(), but using an externally allocated scratch buffer (`workSpace`).
312 * FSE_COMPRESS_WKSP_SIZE_U32() provides the minimum size required for `workSpace` as a table of FSE_CTable.
314 #define FSE_COMPRESS_WKSP_SIZE_U32(maxTableLog, maxSymbolValue) ( FSE_CTABLE_SIZE_U32(maxTableLog, maxSymbolValue) + ((maxTableLog > 12) ? (1 << (maxTableLog - 2)) : 1024) )
315 size_t FSE_compress_wksp (void* dst, size_t dstSize, const void* src, size_t srcSize, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize);
317 size_t FSE_buildCTable_raw (FSE_CTable* ct, unsigned nbBits);
318 /*< build a fake FSE_CTable, designed for a flat distribution, where each symbol uses nbBits */
320 size_t FSE_buildCTable_rle (FSE_CTable* ct, unsigned char symbolValue);
321 /*< build a fake FSE_CTable, designed to compress always the same symbolValue */
323 /* FSE_buildCTable_wksp() :
324 * Same as FSE_buildCTable(), but using an externally allocated scratch buffer (`workSpace`).
325 * `wkspSize` must be >= `FSE_BUILD_CTABLE_WORKSPACE_SIZE_U32(maxSymbolValue, tableLog)` of `unsigned`.
326 * See FSE_buildCTable_wksp() for breakdown of workspace usage.
328 #define FSE_BUILD_CTABLE_WORKSPACE_SIZE_U32(maxSymbolValue, tableLog) (((maxSymbolValue + 2) + (1ull << (tableLog)))/2 + sizeof(U64)/sizeof(U32) /* additional 8 bytes for potential table overwrite */)
329 #define FSE_BUILD_CTABLE_WORKSPACE_SIZE(maxSymbolValue, tableLog) (sizeof(unsigned) * FSE_BUILD_CTABLE_WORKSPACE_SIZE_U32(maxSymbolValue, tableLog))
330 size_t FSE_buildCTable_wksp(FSE_CTable* ct, const short* normalizedCounter, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize);
332 #define FSE_BUILD_DTABLE_WKSP_SIZE(maxTableLog, maxSymbolValue) (sizeof(short) * (maxSymbolValue + 1) + (1ULL << maxTableLog) + 8)
333 #define FSE_BUILD_DTABLE_WKSP_SIZE_U32(maxTableLog, maxSymbolValue) ((FSE_BUILD_DTABLE_WKSP_SIZE(maxTableLog, maxSymbolValue) + sizeof(unsigned) - 1) / sizeof(unsigned))
334 FSE_PUBLIC_API size_t FSE_buildDTable_wksp(FSE_DTable* dt, const short* normalizedCounter, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize);
335 /*< Same as FSE_buildDTable(), using an externally allocated `workspace` produced with `FSE_BUILD_DTABLE_WKSP_SIZE_U32(maxSymbolValue)` */
337 size_t FSE_buildDTable_raw (FSE_DTable* dt, unsigned nbBits);
338 /*< build a fake FSE_DTable, designed to read a flat distribution where each symbol uses nbBits */
340 size_t FSE_buildDTable_rle (FSE_DTable* dt, unsigned char symbolValue);
341 /*< build a fake FSE_DTable, designed to always generate the same symbolValue */
343 #define FSE_DECOMPRESS_WKSP_SIZE_U32(maxTableLog, maxSymbolValue) (FSE_DTABLE_SIZE_U32(maxTableLog) + FSE_BUILD_DTABLE_WKSP_SIZE_U32(maxTableLog, maxSymbolValue) + (FSE_MAX_SYMBOL_VALUE + 1) / 2 + 1)
344 #define FSE_DECOMPRESS_WKSP_SIZE(maxTableLog, maxSymbolValue) (FSE_DECOMPRESS_WKSP_SIZE_U32(maxTableLog, maxSymbolValue) * sizeof(unsigned))
345 size_t FSE_decompress_wksp(void* dst, size_t dstCapacity, const void* cSrc, size_t cSrcSize, unsigned maxLog, void* workSpace, size_t wkspSize);
346 /*< same as FSE_decompress(), using an externally allocated `workSpace` produced with `FSE_DECOMPRESS_WKSP_SIZE_U32(maxLog, maxSymbolValue)` */
348 size_t FSE_decompress_wksp_bmi2(void* dst, size_t dstCapacity, const void* cSrc, size_t cSrcSize, unsigned maxLog, void* workSpace, size_t wkspSize, int bmi2);
349 /*< Same as FSE_decompress_wksp() but with dynamic BMI2 support. Pass 1 if your CPU supports BMI2 or 0 if it doesn't. */
352 FSE_repeat_none, /*< Cannot use the previous table */
353 FSE_repeat_check, /*< Can use the previous table but it must be checked */
354 FSE_repeat_valid /*< Can use the previous table and it is assumed to be valid */
357 /* *****************************************
358 * FSE symbol compression API
359 *******************************************/
361 This API consists of small unitary functions, which highly benefit from being inlined.
362 Hence their body are included in next section.
366 const void* stateTable;
367 const void* symbolTT;
371 static void FSE_initCState(FSE_CState_t* CStatePtr, const FSE_CTable* ct);
373 static void FSE_encodeSymbol(BIT_CStream_t* bitC, FSE_CState_t* CStatePtr, unsigned symbol);
375 static void FSE_flushCState(BIT_CStream_t* bitC, const FSE_CState_t* CStatePtr);
378 These functions are inner components of FSE_compress_usingCTable().
379 They allow the creation of custom streams, mixing multiple tables and bit sources.
381 A key property to keep in mind is that encoding and decoding are done **in reverse direction**.
382 So the first symbol you will encode is the last you will decode, like a LIFO stack.
384 You will need a few variables to track your CStream. They are :
386 FSE_CTable ct; // Provided by FSE_buildCTable()
387 BIT_CStream_t bitStream; // bitStream tracking structure
388 FSE_CState_t state; // State tracking structure (can have several)
390 The first thing to do is to init bitStream and state.
391 size_t errorCode = BIT_initCStream(&bitStream, dstBuffer, maxDstSize);
392 FSE_initCState(&state, ct);
394 Note that BIT_initCStream() can produce an error code, so its result should be tested, using FSE_isError();
395 You can then encode your input data, byte after byte.
396 FSE_encodeSymbol() outputs a maximum of 'tableLog' bits at a time.
397 Remember decoding will be done in reverse direction.
398 FSE_encodeByte(&bitStream, &state, symbol);
400 At any time, you can also add any bit sequence.
401 Note : maximum allowed nbBits is 25, for compatibility with 32-bits decoders
402 BIT_addBits(&bitStream, bitField, nbBits);
404 The above methods don't commit data to memory, they just store it into local register, for speed.
405 Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t).
406 Writing data to memory is a manual operation, performed by the flushBits function.
407 BIT_flushBits(&bitStream);
409 Your last FSE encoding operation shall be to flush your last state value(s).
410 FSE_flushState(&bitStream, &state);
412 Finally, you must close the bitStream.
413 The function returns the size of CStream in bytes.
414 If data couldn't fit into dstBuffer, it will return a 0 ( == not compressible)
415 If there is an error, it returns an errorCode (which can be tested using FSE_isError()).
416 size_t size = BIT_closeCStream(&bitStream);
419 /* *****************************************
420 * FSE symbol decompression API
421 *******************************************/
424 const void* table; /* precise table may vary, depending on U16 */
427 static void FSE_initDState(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD, const FSE_DTable* dt);
429 static unsigned char FSE_decodeSymbol(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD);
431 static unsigned FSE_endOfDState(const FSE_DState_t* DStatePtr);
434 Let's now decompose FSE_decompress_usingDTable() into its unitary components.
435 You will decode FSE-encoded symbols from the bitStream,
436 and also any other bitFields you put in, **in reverse order**.
438 You will need a few variables to track your bitStream. They are :
440 BIT_DStream_t DStream; // Stream context
441 FSE_DState_t DState; // State context. Multiple ones are possible
442 FSE_DTable* DTablePtr; // Decoding table, provided by FSE_buildDTable()
444 The first thing to do is to init the bitStream.
445 errorCode = BIT_initDStream(&DStream, srcBuffer, srcSize);
447 You should then retrieve your initial state(s)
448 (in reverse flushing order if you have several ones) :
449 errorCode = FSE_initDState(&DState, &DStream, DTablePtr);
451 You can then decode your data, symbol after symbol.
452 For information the maximum number of bits read by FSE_decodeSymbol() is 'tableLog'.
453 Keep in mind that symbols are decoded in reverse order, like a LIFO stack (last in, first out).
454 unsigned char symbol = FSE_decodeSymbol(&DState, &DStream);
456 You can retrieve any bitfield you eventually stored into the bitStream (in reverse order)
457 Note : maximum allowed nbBits is 25, for 32-bits compatibility
458 size_t bitField = BIT_readBits(&DStream, nbBits);
460 All above operations only read from local register (which size depends on size_t).
461 Refueling the register from memory is manually performed by the reload method.
462 endSignal = FSE_reloadDStream(&DStream);
464 BIT_reloadDStream() result tells if there is still some more data to read from DStream.
465 BIT_DStream_unfinished : there is still some data left into the DStream.
466 BIT_DStream_endOfBuffer : Dstream reached end of buffer. Its container may no longer be completely filled.
467 BIT_DStream_completed : Dstream reached its exact end, corresponding in general to decompression completed.
468 BIT_DStream_tooFar : Dstream went too far. Decompression result is corrupted.
470 When reaching end of buffer (BIT_DStream_endOfBuffer), progress slowly, notably if you decode multiple symbols per loop,
471 to properly detect the exact end of stream.
472 After each decoded symbol, check if DStream is fully consumed using this simple test :
473 BIT_reloadDStream(&DStream) >= BIT_DStream_completed
475 When it's done, verify decompression is fully completed, by checking both DStream and the relevant states.
476 Checking if DStream has reached its end is performed by :
477 BIT_endOfDStream(&DStream);
478 Check also the states. There might be some symbols left there, if some high probability ones (>50%) are possible.
479 FSE_endOfDState(&DState);
482 /* *****************************************
484 *******************************************/
485 static unsigned char FSE_decodeSymbolFast(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD);
486 /* faster, but works only if nbBits is always >= 1 (otherwise, result will be corrupted) */
488 /* *****************************************
489 * Implementation of inlined functions
490 *******************************************/
494 } FSE_symbolCompressionTransform; /* total 8 bytes */
496 MEM_STATIC void FSE_initCState(FSE_CState_t* statePtr, const FSE_CTable* ct)
498 const void* ptr = ct;
499 const U16* u16ptr = (const U16*) ptr;
500 const U32 tableLog = MEM_read16(ptr);
501 statePtr->value = (ptrdiff_t)1<<tableLog;
502 statePtr->stateTable = u16ptr+2;
503 statePtr->symbolTT = ct + 1 + (tableLog ? (1<<(tableLog-1)) : 1);
504 statePtr->stateLog = tableLog;
507 /*! FSE_initCState2() :
508 * Same as FSE_initCState(), but the first symbol to include (which will be the last to be read)
509 * uses the smallest state value possible, saving the cost of this symbol */
510 MEM_STATIC void FSE_initCState2(FSE_CState_t* statePtr, const FSE_CTable* ct, U32 symbol)
512 FSE_initCState(statePtr, ct);
513 { const FSE_symbolCompressionTransform symbolTT = ((const FSE_symbolCompressionTransform*)(statePtr->symbolTT))[symbol];
514 const U16* stateTable = (const U16*)(statePtr->stateTable);
515 U32 nbBitsOut = (U32)((symbolTT.deltaNbBits + (1<<15)) >> 16);
516 statePtr->value = (nbBitsOut << 16) - symbolTT.deltaNbBits;
517 statePtr->value = stateTable[(statePtr->value >> nbBitsOut) + symbolTT.deltaFindState];
521 MEM_STATIC void FSE_encodeSymbol(BIT_CStream_t* bitC, FSE_CState_t* statePtr, unsigned symbol)
523 FSE_symbolCompressionTransform const symbolTT = ((const FSE_symbolCompressionTransform*)(statePtr->symbolTT))[symbol];
524 const U16* const stateTable = (const U16*)(statePtr->stateTable);
525 U32 const nbBitsOut = (U32)((statePtr->value + symbolTT.deltaNbBits) >> 16);
526 BIT_addBits(bitC, statePtr->value, nbBitsOut);
527 statePtr->value = stateTable[ (statePtr->value >> nbBitsOut) + symbolTT.deltaFindState];
530 MEM_STATIC void FSE_flushCState(BIT_CStream_t* bitC, const FSE_CState_t* statePtr)
532 BIT_addBits(bitC, statePtr->value, statePtr->stateLog);
536 /* FSE_getMaxNbBits() :
537 * Approximate maximum cost of a symbol, in bits.
538 * Fractional get rounded up (i.e : a symbol with a normalized frequency of 3 gives the same result as a frequency of 2)
539 * note 1 : assume symbolValue is valid (<= maxSymbolValue)
540 * note 2 : if freq[symbolValue]==0, @return a fake cost of tableLog+1 bits */
541 MEM_STATIC U32 FSE_getMaxNbBits(const void* symbolTTPtr, U32 symbolValue)
543 const FSE_symbolCompressionTransform* symbolTT = (const FSE_symbolCompressionTransform*) symbolTTPtr;
544 return (symbolTT[symbolValue].deltaNbBits + ((1<<16)-1)) >> 16;
548 * Approximate symbol cost, as fractional value, using fixed-point format (accuracyLog fractional bits)
549 * note 1 : assume symbolValue is valid (<= maxSymbolValue)
550 * note 2 : if freq[symbolValue]==0, @return a fake cost of tableLog+1 bits */
551 MEM_STATIC U32 FSE_bitCost(const void* symbolTTPtr, U32 tableLog, U32 symbolValue, U32 accuracyLog)
553 const FSE_symbolCompressionTransform* symbolTT = (const FSE_symbolCompressionTransform*) symbolTTPtr;
554 U32 const minNbBits = symbolTT[symbolValue].deltaNbBits >> 16;
555 U32 const threshold = (minNbBits+1) << 16;
556 assert(tableLog < 16);
557 assert(accuracyLog < 31-tableLog); /* ensure enough room for renormalization double shift */
558 { U32 const tableSize = 1 << tableLog;
559 U32 const deltaFromThreshold = threshold - (symbolTT[symbolValue].deltaNbBits + tableSize);
560 U32 const normalizedDeltaFromThreshold = (deltaFromThreshold << accuracyLog) >> tableLog; /* linear interpolation (very approximate) */
561 U32 const bitMultiplier = 1 << accuracyLog;
562 assert(symbolTT[symbolValue].deltaNbBits + tableSize <= threshold);
563 assert(normalizedDeltaFromThreshold <= bitMultiplier);
564 return (minNbBits+1)*bitMultiplier - normalizedDeltaFromThreshold;
568 /* ====== Decompression ====== */
573 } FSE_DTableHeader; /* sizeof U32 */
577 unsigned short newState;
578 unsigned char symbol;
579 unsigned char nbBits;
580 } FSE_decode_t; /* size == U32 */
582 MEM_STATIC void FSE_initDState(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD, const FSE_DTable* dt)
584 const void* ptr = dt;
585 const FSE_DTableHeader* const DTableH = (const FSE_DTableHeader*)ptr;
586 DStatePtr->state = BIT_readBits(bitD, DTableH->tableLog);
587 BIT_reloadDStream(bitD);
588 DStatePtr->table = dt + 1;
591 MEM_STATIC BYTE FSE_peekSymbol(const FSE_DState_t* DStatePtr)
593 FSE_decode_t const DInfo = ((const FSE_decode_t*)(DStatePtr->table))[DStatePtr->state];
597 MEM_STATIC void FSE_updateState(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD)
599 FSE_decode_t const DInfo = ((const FSE_decode_t*)(DStatePtr->table))[DStatePtr->state];
600 U32 const nbBits = DInfo.nbBits;
601 size_t const lowBits = BIT_readBits(bitD, nbBits);
602 DStatePtr->state = DInfo.newState + lowBits;
605 MEM_STATIC BYTE FSE_decodeSymbol(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD)
607 FSE_decode_t const DInfo = ((const FSE_decode_t*)(DStatePtr->table))[DStatePtr->state];
608 U32 const nbBits = DInfo.nbBits;
609 BYTE const symbol = DInfo.symbol;
610 size_t const lowBits = BIT_readBits(bitD, nbBits);
612 DStatePtr->state = DInfo.newState + lowBits;
616 /*! FSE_decodeSymbolFast() :
617 unsafe, only works if no symbol has a probability > 50% */
618 MEM_STATIC BYTE FSE_decodeSymbolFast(FSE_DState_t* DStatePtr, BIT_DStream_t* bitD)
620 FSE_decode_t const DInfo = ((const FSE_decode_t*)(DStatePtr->table))[DStatePtr->state];
621 U32 const nbBits = DInfo.nbBits;
622 BYTE const symbol = DInfo.symbol;
623 size_t const lowBits = BIT_readBitsFast(bitD, nbBits);
625 DStatePtr->state = DInfo.newState + lowBits;
629 MEM_STATIC unsigned FSE_endOfDState(const FSE_DState_t* DStatePtr)
631 return DStatePtr->state == 0;
634 #ifndef FSE_COMMONDEFS_ONLY
636 /* **************************************************************
638 ****************************************************************/
640 * Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.)
641 * Increasing memory usage improves compression ratio
642 * Reduced memory usage can improve speed, due to cache effect
643 * Recommended max value is 14, for 16KB, which nicely fits into Intel x86 L1 cache */
644 #ifndef FSE_MAX_MEMORY_USAGE
645 # define FSE_MAX_MEMORY_USAGE 14
647 #ifndef FSE_DEFAULT_MEMORY_USAGE
648 # define FSE_DEFAULT_MEMORY_USAGE 13
650 #if (FSE_DEFAULT_MEMORY_USAGE > FSE_MAX_MEMORY_USAGE)
651 # error "FSE_DEFAULT_MEMORY_USAGE must be <= FSE_MAX_MEMORY_USAGE"
654 /*!FSE_MAX_SYMBOL_VALUE :
655 * Maximum symbol value authorized.
656 * Required for proper stack allocation */
657 #ifndef FSE_MAX_SYMBOL_VALUE
658 # define FSE_MAX_SYMBOL_VALUE 255
661 /* **************************************************************
662 * template functions type & suffix
663 ****************************************************************/
664 #define FSE_FUNCTION_TYPE BYTE
665 #define FSE_FUNCTION_EXTENSION
666 #define FSE_DECODE_TYPE FSE_decode_t
668 #endif /* !FSE_COMMONDEFS_ONLY */
670 /* ***************************************************************
672 *****************************************************************/
673 #define FSE_MAX_TABLELOG (FSE_MAX_MEMORY_USAGE-2)
674 #define FSE_MAX_TABLESIZE (1U<<FSE_MAX_TABLELOG)
675 #define FSE_MAXTABLESIZE_MASK (FSE_MAX_TABLESIZE-1)
676 #define FSE_DEFAULT_TABLELOG (FSE_DEFAULT_MEMORY_USAGE-2)
677 #define FSE_MIN_TABLELOG 5
679 #define FSE_TABLELOG_ABSOLUTE_MAX 15
680 #if FSE_MAX_TABLELOG > FSE_TABLELOG_ABSOLUTE_MAX
681 # error "FSE_MAX_TABLELOG > FSE_TABLELOG_ABSOLUTE_MAX is not supported"
684 #define FSE_TABLESTEP(tableSize) (((tableSize)>>1) + ((tableSize)>>3) + 3)
686 #endif /* FSE_STATIC_LINKING_ONLY */