lib/zstd/fse.h

   1 /*
   2  * FSE : Finite State Entropy codec
   3  * Public Prototypes declaration
   4  * Copyright (C) 2013-2016, Yann Collet.
   5  *
   6  * BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions are
  10  * met:
  11  *
  12  *   * Redistributions of source code must retain the above copyright
  13  * notice, this list of conditions and the following disclaimer.
  14  *   * Redistributions in binary form must reproduce the above
  15  * copyright notice, this list of conditions and the following disclaimer
  16  * in the documentation and/or other materials provided with the
  17  * distribution.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  20  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  21  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  22  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  23  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  26  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  27  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  28  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  29  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  30  *
  31  * This program is free software; you can redistribute it and/or modify it under
  32  * the terms of the GNU General Public License version 2 as published by the
  33  * Free Software Foundation. This program is dual-licensed; you may select
  34  * either version 2 of the GNU General Public License ("GPL") or BSD license
  35  * ("BSD").
  36  *
  37  * You can contact the author at :
  38  * - Source repository : https://github.com/Cyan4973/FiniteStateEntropy
  39  */
  40 #ifndef FSE_H
  41 #define FSE_H
  42
  43 /*-*****************************************
  44 *  Dependencies
  45 ******************************************/
  46 #include <linux/types.h> /* size_t, ptrdiff_t */
  47
  48 /*-*****************************************
  49 *  FSE_PUBLIC_API : control library symbols visibility
  50 ******************************************/
  51 #define FSE_PUBLIC_API
  52
  53 /*------   Version   ------*/
  54 #define FSE_VERSION_MAJOR 0
  55 #define FSE_VERSION_MINOR 9
  56 #define FSE_VERSION_RELEASE 0
  57
  58 #define FSE_LIB_VERSION FSE_VERSION_MAJOR.FSE_VERSION_MINOR.FSE_VERSION_RELEASE
  59 #define FSE_QUOTE(str) #str
  60 #define FSE_EXPAND_AND_QUOTE(str) FSE_QUOTE(str)
  61 #define FSE_VERSION_STRING FSE_EXPAND_AND_QUOTE(FSE_LIB_VERSION)
  62
  63 #define FSE_VERSION_NUMBER (FSE_VERSION_MAJOR * 100 * 100 + FSE_VERSION_MINOR * 100 + FSE_VERSION_RELEASE)
  64 FSE_PUBLIC_API unsigned FSE_versionNumber(void); /**< library version number; to be used when checking dll version */
  65
  66 /*-*****************************************
  67 *  Tool functions
  68 ******************************************/
  69 FSE_PUBLIC_API size_t FSE_compressBound(size_t size); /* maximum compressed size */
  70
  71 /* Error Management */
  72 FSE_PUBLIC_API unsigned FSE_isError(size_t code); /* tells if a return value is an error code */
  73
  74 /*-*****************************************
  75 *  FSE detailed API
  76 ******************************************/
  77 /*!
  78 FSE_compress() does the following:
  79 1. count symbol occurrence from source[] into table count[]
  80 2. normalize counters so that sum(count[]) == Power_of_2 (2^tableLog)
  81 3. save normalized counters to memory buffer using writeNCount()
  82 4. build encoding table 'CTable' from normalized counters
  83 5. encode the data stream using encoding table 'CTable'
  84
  85 FSE_decompress() does the following:
  86 1. read normalized counters with readNCount()
  87 2. build decoding table 'DTable' from normalized counters
  88 3. decode the data stream using decoding table 'DTable'
  89
  90 The following API allows targeting specific sub-functions for advanced tasks.
  91 For example, it's possible to compress several blocks using the same 'CTable',
  92 or to save and provide normalized distribution using external method.
  93 */
  94
  95 /* *** COMPRESSION *** */
  96 /*! FSE_optimalTableLog():
  97         dynamically downsize 'tableLog' when conditions are met.
  98         It saves CPU time, by using smaller tables, while preserving or even improving compression ratio.
  99         @return : recommended tableLog (necessarily <= 'maxTableLog') */
 100 FSE_PUBLIC_API unsigned FSE_optimalTableLog(unsigned maxTableLog, size_t srcSize, unsigned maxSymbolValue);
 101
 102 /*! FSE_normalizeCount():
 103         normalize counts so that sum(count[]) == Power_of_2 (2^tableLog)
 104         'normalizedCounter' is a table of short, of minimum size (maxSymbolValue+1).
 105         @return : tableLog,
 106                           or an errorCode, which can be tested using FSE_isError() */
 107 FSE_PUBLIC_API size_t FSE_normalizeCount(short *normalizedCounter, unsigned tableLog, const unsigned *count, size_t srcSize, unsigned maxSymbolValue);
 108
 109 /*! FSE_NCountWriteBound():
 110         Provides the maximum possible size of an FSE normalized table, given 'maxSymbolValue' and 'tableLog'.
 111         Typically useful for allocation purpose. */
 112 FSE_PUBLIC_API size_t FSE_NCountWriteBound(unsigned maxSymbolValue, unsigned tableLog);
 113
 114 /*! FSE_writeNCount():
 115         Compactly save 'normalizedCounter' into 'buffer'.
 116         @return : size of the compressed table,
 117                           or an errorCode, which can be tested using FSE_isError(). */
 118 FSE_PUBLIC_API size_t FSE_writeNCount(void *buffer, size_t bufferSize, const short *normalizedCounter, unsigned maxSymbolValue, unsigned tableLog);
 119
 120 /*! Constructor and Destructor of FSE_CTable.
 121         Note that FSE_CTable size depends on 'tableLog' and 'maxSymbolValue' */
 122 typedef unsigned FSE_CTable; /* don't allocate that. It's only meant to be more restrictive than void* */
 123
 124 /*! FSE_compress_usingCTable():
 125         Compress `src` using `ct` into `dst` which must be already allocated.
 126         @return : size of compressed data (<= `dstCapacity`),
 127                           or 0 if compressed data could not fit into `dst`,
 128                           or an errorCode, which can be tested using FSE_isError() */
 129 FSE_PUBLIC_API size_t FSE_compress_usingCTable(void *dst, size_t dstCapacity, const void *src, size_t srcSize, const FSE_CTable *ct);
 130
 131 /*!
 132 Tutorial :
 133 ----------
 134 The first step is to count all symbols. FSE_count() does this job very fast.
 135 Result will be saved into 'count', a table of unsigned int, which must be already allocated, and have 'maxSymbolValuePtr[0]+1' cells.
 136 'src' is a table of bytes of size 'srcSize'. All values within 'src' MUST be <= maxSymbolValuePtr[0]
 137 maxSymbolValuePtr[0] will be updated, with its real value (necessarily <= original value)
 138 FSE_count() will return the number of occurrence of the most frequent symbol.
 139 This can be used to know if there is a single symbol within 'src', and to quickly evaluate its compressibility.
 140 If there is an error, the function will return an ErrorCode (which can be tested using FSE_isError()).
 141
 142 The next step is to normalize the frequencies.
 143 FSE_normalizeCount() will ensure that sum of frequencies is == 2 ^'tableLog'.
 144 It also guarantees a minimum of 1 to any Symbol with frequency >= 1.
 145 You can use 'tableLog'==0 to mean "use default tableLog value".
 146 If you are unsure of which tableLog value to use, you can ask FSE_optimalTableLog(),
 147 which will provide the optimal valid tableLog given sourceSize, maxSymbolValue, and a user-defined maximum (0 means "default").
 148
 149 The result of FSE_normalizeCount() will be saved into a table,
 150 called 'normalizedCounter', which is a table of signed short.
 151 'normalizedCounter' must be already allocated, and have at least 'maxSymbolValue+1' cells.
 152 The return value is tableLog if everything proceeded as expected.
 153 It is 0 if there is a single symbol within distribution.
 154 If there is an error (ex: invalid tableLog value), the function will return an ErrorCode (which can be tested using FSE_isError()).
 155
 156 'normalizedCounter' can be saved in a compact manner to a memory area using FSE_writeNCount().
 157 'buffer' must be already allocated.
 158 For guaranteed success, buffer size must be at least FSE_headerBound().
 159 The result of the function is the number of bytes written into 'buffer'.
 160 If there is an error, the function will return an ErrorCode (which can be tested using FSE_isError(); ex : buffer size too small).
 161
 162 'normalizedCounter' can then be used to create the compression table 'CTable'.
 163 The space required by 'CTable' must be already allocated, using FSE_createCTable().
 164 You can then use FSE_buildCTable() to fill 'CTable'.
 165 If there is an error, both functions will return an ErrorCode (which can be tested using FSE_isError()).
 166
 167 'CTable' can then be used to compress 'src', with FSE_compress_usingCTable().
 168 Similar to FSE_count(), the convention is that 'src' is assumed to be a table of char of size 'srcSize'
 169 The function returns the size of compressed data (without header), necessarily <= `dstCapacity`.
 170 If it returns '0', compressed data could not fit into 'dst'.
 171 If there is an error, the function will return an ErrorCode (which can be tested using FSE_isError()).
 172 */
 173
 174 /* *** DECOMPRESSION *** */
 175
 176 /*! FSE_readNCount():
 177         Read compactly saved 'normalizedCounter' from 'rBuffer'.
 178         @return : size read from 'rBuffer',
 179                           or an errorCode, which can be tested using FSE_isError().
 180                           maxSymbolValuePtr[0] and tableLogPtr[0] will also be updated with their respective values */
 181 FSE_PUBLIC_API size_t FSE_readNCount(short *normalizedCounter, unsigned *maxSymbolValuePtr, unsigned *tableLogPtr, const void *rBuffer, size_t rBuffSize);
 182
 183 /*! Constructor and Destructor of FSE_DTable.
 184         Note that its size depends on 'tableLog' */
 185 typedef unsigned FSE_DTable; /* don't allocate that. It's just a way to be more restrictive than void* */
 186
 187 /*! FSE_buildDTable():
 188         Builds 'dt', which must be already allocated, using FSE_createDTable().
 189         return : 0, or an errorCode, which can be tested using FSE_isError() */
 190 FSE_PUBLIC_API size_t FSE_buildDTable_wksp(FSE_DTable *dt, const short *normalizedCounter, unsigned maxSymbolValue, unsigned tableLog, void *workspace, size_t workspaceSize);
 191
 192 /*! FSE_decompress_usingDTable():
 193         Decompress compressed source `cSrc` of size `cSrcSize` using `dt`
 194         into `dst` which must be already allocated.
 195         @return : size of regenerated data (necessarily <= `dstCapacity`),
 196                           or an errorCode, which can be tested using FSE_isError() */
 197 FSE_PUBLIC_API size_t FSE_decompress_usingDTable(void *dst, size_t dstCapacity, const void *cSrc, size_t cSrcSize, const FSE_DTable *dt);
 198
 199 /*!
 200 Tutorial :
 201 ----------
 202 (Note : these functions only decompress FSE-compressed blocks.
 203  If block is uncompressed, use memcpy() instead
 204  If block is a single repeated byte, use memset() instead )
 205
 206 The first step is to obtain the normalized frequencies of symbols.
 207 This can be performed by FSE_readNCount() if it was saved using FSE_writeNCount().
 208 'normalizedCounter' must be already allocated, and have at least 'maxSymbolValuePtr[0]+1' cells of signed short.
 209 In practice, that means it's necessary to know 'maxSymbolValue' beforehand,
 210 or size the table to handle worst case situations (typically 256).
 211 FSE_readNCount() will provide 'tableLog' and 'maxSymbolValue'.
 212 The result of FSE_readNCount() is the number of bytes read from 'rBuffer'.
 213 Note that 'rBufferSize' must be at least 4 bytes, even if useful information is less than that.
 214 If there is an error, the function will return an error code, which can be tested using FSE_isError().
 215
 216 The next step is to build the decompression tables 'FSE_DTable' from 'normalizedCounter'.
 217 This is performed by the function FSE_buildDTable().
 218 The space required by 'FSE_DTable' must be already allocated using FSE_createDTable().
 219 If there is an error, the function will return an error code, which can be tested using FSE_isError().
 220
 221 `FSE_DTable` can then be used to decompress `cSrc`, with FSE_decompress_usingDTable().
 222 `cSrcSize` must be strictly correct, otherwise decompression will fail.
 223 FSE_decompress_usingDTable() result will tell how many bytes were regenerated (<=`dstCapacity`).
 224 If there is an error, the function will return an error code, which can be tested using FSE_isError(). (ex: dst buffer too small)
 225 */
 226
 227 /* *** Dependency *** */
 228 #include "bitstream.h"
 229
 230 /* *****************************************
 231 *  Static allocation
 232 *******************************************/
 233 /* FSE buffer bounds */
 234 #define FSE_NCOUNTBOUND 512
 235 #define FSE_BLOCKBOUND(size) (size + (size >> 7))
 236 #define FSE_COMPRESSBOUND(size) (FSE_NCOUNTBOUND + FSE_BLOCKBOUND(size)) /* Macro version, useful for static allocation */
 237
 238 /* It is possible to statically allocate FSE CTable/DTable as a table of FSE_CTable/FSE_DTable using below macros */
 239 #define FSE_CTABLE_SIZE_U32(maxTableLog, maxSymbolValue) (1 + (1 << (maxTableLog - 1)) + ((maxSymbolValue + 1) * 2))
 240 #define FSE_DTABLE_SIZE_U32(maxTableLog) (1 + (1 << maxTableLog))
 241
 242 /* *****************************************
 243 *  FSE advanced API
 244 *******************************************/
 245 /* FSE_count_wksp() :
 246  * Same as FSE_count(), but using an externally provided scratch buffer.
 247  * `workSpace` size must be table of >= `1024` unsigned
 248  */
 249 size_t FSE_count_wksp(unsigned *count, unsigned *maxSymbolValuePtr, const void *source, size_t sourceSize, unsigned *workSpace);
 250
 251 /* FSE_countFast_wksp() :
 252  * Same as FSE_countFast(), but using an externally provided scratch buffer.
 253  * `workSpace` must be a table of minimum `1024` unsigned
 254  */
 255 size_t FSE_countFast_wksp(unsigned *count, unsigned *maxSymbolValuePtr, const void *src, size_t srcSize, unsigned *workSpace);
 256
 257 /*! FSE_count_simple
 258  * Same as FSE_countFast(), but does not use any additional memory (not even on stack).
 259  * This function is unsafe, and will segfault if any value within `src` is `> *maxSymbolValuePtr` (presuming it's also the size of `count`).
 260 */
 261 size_t FSE_count_simple(unsigned *count, unsigned *maxSymbolValuePtr, const void *src, size_t srcSize);
 262
 263 unsigned FSE_optimalTableLog_internal(unsigned maxTableLog, size_t srcSize, unsigned maxSymbolValue, unsigned minus);
 264 /**< same as FSE_optimalTableLog(), which used `minus==2` */
 265
 266 size_t FSE_buildCTable_raw(FSE_CTable *ct, unsigned nbBits);
 267 /**< build a fake FSE_CTable, designed for a flat distribution, where each symbol uses nbBits */
 268
 269 size_t FSE_buildCTable_rle(FSE_CTable *ct, unsigned char symbolValue);
 270 /**< build a fake FSE_CTable, designed to compress always the same symbolValue */
 271
 272 /* FSE_buildCTable_wksp() :
 273  * Same as FSE_buildCTable(), but using an externally allocated scratch buffer (`workSpace`).
 274  * `wkspSize` must be >= `(1<<tableLog)`.
 275  */
 276 size_t FSE_buildCTable_wksp(FSE_CTable *ct, const short *normalizedCounter, unsigned maxSymbolValue, unsigned tableLog, void *workSpace, size_t wkspSize);
 277
 278 size_t FSE_buildDTable_raw(FSE_DTable *dt, unsigned nbBits);
 279 /**< build a fake FSE_DTable, designed to read a flat distribution where each symbol uses nbBits */
 280
 281 size_t FSE_buildDTable_rle(FSE_DTable *dt, unsigned char symbolValue);
 282 /**< build a fake FSE_DTable, designed to always generate the same symbolValue */
 283
 284 size_t FSE_decompress_wksp(void *dst, size_t dstCapacity, const void *cSrc, size_t cSrcSize, unsigned maxLog, void *workspace, size_t workspaceSize);
 285 /**< same as FSE_decompress(), using an externally allocated `workSpace` produced with `FSE_DTABLE_SIZE_U32(maxLog)` */
 286
 287 /* *****************************************
 288 *  FSE symbol compression API
 289 *******************************************/
 290 /*!
 291    This API consists of small unitary functions, which highly benefit from being inlined.
 292    Hence their body are included in next section.
 293 */
 294 typedef struct {
 295         ptrdiff_t value;
 296         const void *stateTable;
 297         const void *symbolTT;
 298         unsigned stateLog;
 299 } FSE_CState_t;
 300
 301 static void FSE_initCState(FSE_CState_t *CStatePtr, const FSE_CTable *ct);
 302
 303 static void FSE_encodeSymbol(BIT_CStream_t *bitC, FSE_CState_t *CStatePtr, unsigned symbol);
 304
 305 static void FSE_flushCState(BIT_CStream_t *bitC, const FSE_CState_t *CStatePtr);
 306
 307 /**<
 308 These functions are inner components of FSE_compress_usingCTable().
 309 They allow the creation of custom streams, mixing multiple tables and bit sources.
 310
 311 A key property to keep in mind is that encoding and decoding are done **in reverse direction**.
 312 So the first symbol you will encode is the last you will decode, like a LIFO stack.
 313
 314 You will need a few variables to track your CStream. They are :
 315
 316 FSE_CTable    ct;         // Provided by FSE_buildCTable()
 317 BIT_CStream_t bitStream;  // bitStream tracking structure
 318 FSE_CState_t  state;      // State tracking structure (can have several)
 319
 320
 321 The first thing to do is to init bitStream and state.
 322         size_t errorCode = BIT_initCStream(&bitStream, dstBuffer, maxDstSize);
 323         FSE_initCState(&state, ct);
 324
 325 Note that BIT_initCStream() can produce an error code, so its result should be tested, using FSE_isError();
 326 You can then encode your input data, byte after byte.
 327 FSE_encodeSymbol() outputs a maximum of 'tableLog' bits at a time.
 328 Remember decoding will be done in reverse direction.
 329         FSE_encodeByte(&bitStream, &state, symbol);
 330
 331 At any time, you can also add any bit sequence.
 332 Note : maximum allowed nbBits is 25, for compatibility with 32-bits decoders
 333         BIT_addBits(&bitStream, bitField, nbBits);
 334
 335 The above methods don't commit data to memory, they just store it into local register, for speed.
 336 Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t).
 337 Writing data to memory is a manual operation, performed by the flushBits function.
 338         BIT_flushBits(&bitStream);
 339
 340 Your last FSE encoding operation shall be to flush your last state value(s).
 341         FSE_flushState(&bitStream, &state);
 342
 343 Finally, you must close the bitStream.
 344 The function returns the size of CStream in bytes.
 345 If data couldn't fit into dstBuffer, it will return a 0 ( == not compressible)
 346 If there is an error, it returns an errorCode (which can be tested using FSE_isError()).
 347         size_t size = BIT_closeCStream(&bitStream);
 348 */
 349
 350 /* *****************************************
 351 *  FSE symbol decompression API
 352 *******************************************/
 353 typedef struct {
 354         size_t state;
 355         const void *table; /* precise table may vary, depending on U16 */
 356 } FSE_DState_t;
 357
 358 static void FSE_initDState(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD, const FSE_DTable *dt);
 359
 360 static unsigned char FSE_decodeSymbol(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD);
 361
 362 static unsigned FSE_endOfDState(const FSE_DState_t *DStatePtr);
 363
 364 /**<
 365 Let's now decompose FSE_decompress_usingDTable() into its unitary components.
 366 You will decode FSE-encoded symbols from the bitStream,
 367 and also any other bitFields you put in, **in reverse order**.
 368
 369 You will need a few variables to track your bitStream. They are :
 370
 371 BIT_DStream_t DStream;    // Stream context
 372 FSE_DState_t  DState;     // State context. Multiple ones are possible
 373 FSE_DTable*   DTablePtr;  // Decoding table, provided by FSE_buildDTable()
 374
 375 The first thing to do is to init the bitStream.
 376         errorCode = BIT_initDStream(&DStream, srcBuffer, srcSize);
 377
 378 You should then retrieve your initial state(s)
 379 (in reverse flushing order if you have several ones) :
 380         errorCode = FSE_initDState(&DState, &DStream, DTablePtr);
 381
 382 You can then decode your data, symbol after symbol.
 383 For information the maximum number of bits read by FSE_decodeSymbol() is 'tableLog'.
 384 Keep in mind that symbols are decoded in reverse order, like a LIFO stack (last in, first out).
 385         unsigned char symbol = FSE_decodeSymbol(&DState, &DStream);
 386
 387 You can retrieve any bitfield you eventually stored into the bitStream (in reverse order)
 388 Note : maximum allowed nbBits is 25, for 32-bits compatibility
 389         size_t bitField = BIT_readBits(&DStream, nbBits);
 390
 391 All above operations only read from local register (which size depends on size_t).
 392 Refueling the register from memory is manually performed by the reload method.
 393         endSignal = FSE_reloadDStream(&DStream);
 394
 395 BIT_reloadDStream() result tells if there is still some more data to read from DStream.
 396 BIT_DStream_unfinished : there is still some data left into the DStream.
 397 BIT_DStream_endOfBuffer : Dstream reached end of buffer. Its container may no longer be completely filled.
 398 BIT_DStream_completed : Dstream reached its exact end, corresponding in general to decompression completed.
 399 BIT_DStream_tooFar : Dstream went too far. Decompression result is corrupted.
 400
 401 When reaching end of buffer (BIT_DStream_endOfBuffer), progress slowly, notably if you decode multiple symbols per loop,
 402 to properly detect the exact end of stream.
 403 After each decoded symbol, check if DStream is fully consumed using this simple test :
 404         BIT_reloadDStream(&DStream) >= BIT_DStream_completed
 405
 406 When it's done, verify decompression is fully completed, by checking both DStream and the relevant states.
 407 Checking if DStream has reached its end is performed by :
 408         BIT_endOfDStream(&DStream);
 409 Check also the states. There might be some symbols left there, if some high probability ones (>50%) are possible.
 410         FSE_endOfDState(&DState);
 411 */
 412
 413 /* *****************************************
 414 *  FSE unsafe API
 415 *******************************************/
 416 static unsigned char FSE_decodeSymbolFast(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD);
 417 /* faster, but works only if nbBits is always >= 1 (otherwise, result will be corrupted) */
 418
 419 /* *****************************************
 420 *  Implementation of inlined functions
 421 *******************************************/
 422 typedef struct {
 423         int deltaFindState;
 424         U32 deltaNbBits;
 425 } FSE_symbolCompressionTransform; /* total 8 bytes */
 426
 427 ZSTD_STATIC void FSE_initCState(FSE_CState_t *statePtr, const FSE_CTable *ct)
 428 {
 429         const void *ptr = ct;
 430         const U16 *u16ptr = (const U16 *)ptr;
 431         const U32 tableLog = ZSTD_read16(ptr);
 432         statePtr->value = (ptrdiff_t)1 << tableLog;
 433         statePtr->stateTable = u16ptr + 2;
 434         statePtr->symbolTT = ((const U32 *)ct + 1 + (tableLog ? (1 << (tableLog - 1)) : 1));
 435         statePtr->stateLog = tableLog;
 436 }
 437
 438 /*! FSE_initCState2() :
 439 *   Same as FSE_initCState(), but the first symbol to include (which will be the last to be read)
 440 *   uses the smallest state value possible, saving the cost of this symbol */
 441 ZSTD_STATIC void FSE_initCState2(FSE_CState_t *statePtr, const FSE_CTable *ct, U32 symbol)
 442 {
 443         FSE_initCState(statePtr, ct);
 444         {
 445                 const FSE_symbolCompressionTransform symbolTT = ((const FSE_symbolCompressionTransform *)(statePtr->symbolTT))[symbol];
 446                 const U16 *stateTable = (const U16 *)(statePtr->stateTable);
 447                 U32 nbBitsOut = (U32)((symbolTT.deltaNbBits + (1 << 15)) >> 16);
 448                 statePtr->value = (nbBitsOut << 16) - symbolTT.deltaNbBits;
 449                 statePtr->value = stateTable[(statePtr->value >> nbBitsOut) + symbolTT.deltaFindState];
 450         }
 451 }
 452
 453 ZSTD_STATIC void FSE_encodeSymbol(BIT_CStream_t *bitC, FSE_CState_t *statePtr, U32 symbol)
 454 {
 455         const FSE_symbolCompressionTransform symbolTT = ((const FSE_symbolCompressionTransform *)(statePtr->symbolTT))[symbol];
 456         const U16 *const stateTable = (const U16 *)(statePtr->stateTable);
 457         U32 nbBitsOut = (U32)((statePtr->value + symbolTT.deltaNbBits) >> 16);
 458         BIT_addBits(bitC, statePtr->value, nbBitsOut);
 459         statePtr->value = stateTable[(statePtr->value >> nbBitsOut) + symbolTT.deltaFindState];
 460 }
 461
 462 ZSTD_STATIC void FSE_flushCState(BIT_CStream_t *bitC, const FSE_CState_t *statePtr)
 463 {
 464         BIT_addBits(bitC, statePtr->value, statePtr->stateLog);
 465         BIT_flushBits(bitC);
 466 }
 467
 468 /* ======    Decompression    ====== */
 469
 470 typedef struct {
 471         U16 tableLog;
 472         U16 fastMode;
 473 } FSE_DTableHeader; /* sizeof U32 */
 474
 475 typedef struct {
 476         unsigned short newState;
 477         unsigned char symbol;
 478         unsigned char nbBits;
 479 } FSE_decode_t; /* size == U32 */
 480
 481 ZSTD_STATIC void FSE_initDState(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD, const FSE_DTable *dt)
 482 {
 483         const void *ptr = dt;
 484         const FSE_DTableHeader *const DTableH = (const FSE_DTableHeader *)ptr;
 485         DStatePtr->state = BIT_readBits(bitD, DTableH->tableLog);
 486         BIT_reloadDStream(bitD);
 487         DStatePtr->table = dt + 1;
 488 }
 489
 490 ZSTD_STATIC BYTE FSE_peekSymbol(const FSE_DState_t *DStatePtr)
 491 {
 492         FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state];
 493         return DInfo.symbol;
 494 }
 495
 496 ZSTD_STATIC void FSE_updateState(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD)
 497 {
 498         FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state];
 499         U32 const nbBits = DInfo.nbBits;
 500         size_t const lowBits = BIT_readBits(bitD, nbBits);
 501         DStatePtr->state = DInfo.newState + lowBits;
 502 }
 503
 504 ZSTD_STATIC BYTE FSE_decodeSymbol(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD)
 505 {
 506         FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state];
 507         U32 const nbBits = DInfo.nbBits;
 508         BYTE const symbol = DInfo.symbol;
 509         size_t const lowBits = BIT_readBits(bitD, nbBits);
 510
 511         DStatePtr->state = DInfo.newState + lowBits;
 512         return symbol;
 513 }
 514
 515 /*! FSE_decodeSymbolFast() :
 516         unsafe, only works if no symbol has a probability > 50% */
 517 ZSTD_STATIC BYTE FSE_decodeSymbolFast(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD)
 518 {
 519         FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state];
 520         U32 const nbBits = DInfo.nbBits;
 521         BYTE const symbol = DInfo.symbol;
 522         size_t const lowBits = BIT_readBitsFast(bitD, nbBits);
 523
 524         DStatePtr->state = DInfo.newState + lowBits;
 525         return symbol;
 526 }
 527
 528 ZSTD_STATIC unsigned FSE_endOfDState(const FSE_DState_t *DStatePtr) { return DStatePtr->state == 0; }
 529
 530 /* **************************************************************
 531 *  Tuning parameters
 532 ****************************************************************/
 533 /*!MEMORY_USAGE :
 534 *  Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.)
 535 *  Increasing memory usage improves compression ratio
 536 *  Reduced memory usage can improve speed, due to cache effect
 537 *  Recommended max value is 14, for 16KB, which nicely fits into Intel x86 L1 cache */
 538 #ifndef FSE_MAX_MEMORY_USAGE
 539 #define FSE_MAX_MEMORY_USAGE 14
 540 #endif
 541 #ifndef FSE_DEFAULT_MEMORY_USAGE
 542 #define FSE_DEFAULT_MEMORY_USAGE 13
 543 #endif
 544
 545 /*!FSE_MAX_SYMBOL_VALUE :
 546 *  Maximum symbol value authorized.
 547 *  Required for proper stack allocation */
 548 #ifndef FSE_MAX_SYMBOL_VALUE
 549 #define FSE_MAX_SYMBOL_VALUE 255
 550 #endif
 551
 552 /* **************************************************************
 553 *  template functions type & suffix
 554 ****************************************************************/
 555 #define FSE_FUNCTION_TYPE BYTE
 556 #define FSE_FUNCTION_EXTENSION
 557 #define FSE_DECODE_TYPE FSE_decode_t
 558
 559 /* ***************************************************************
 560 *  Constants
 561 *****************************************************************/
 562 #define FSE_MAX_TABLELOG (FSE_MAX_MEMORY_USAGE - 2)
 563 #define FSE_MAX_TABLESIZE (1U << FSE_MAX_TABLELOG)
 564 #define FSE_MAXTABLESIZE_MASK (FSE_MAX_TABLESIZE - 1)
 565 #define FSE_DEFAULT_TABLELOG (FSE_DEFAULT_MEMORY_USAGE - 2)
 566 #define FSE_MIN_TABLELOG 5
 567
 568 #define FSE_TABLELOG_ABSOLUTE_MAX 15
 569 #if FSE_MAX_TABLELOG > FSE_TABLELOG_ABSOLUTE_MAX
 570 #error "FSE_MAX_TABLELOG > FSE_TABLELOG_ABSOLUTE_MAX is not supported"
 571 #endif
 572
 573 #define FSE_TABLESTEP(tableSize) ((tableSize >> 1) + (tableSize >> 3) + 3)
 574
 575 #endif /* FSE_H */