diff options
Diffstat (limited to 'lib/zstd/fse.h')
| -rw-r--r-- | lib/zstd/fse.h | 545 |
1 files changed, 545 insertions, 0 deletions
diff --git a/lib/zstd/fse.h b/lib/zstd/fse.h new file mode 100644 index 0000000000..42f80ff73e --- /dev/null +++ b/lib/zstd/fse.h @@ -0,0 +1,545 @@ +/* SPDX-License-Identifier: (GPL-2.0 or BSD-2-Clause) */ +/* + * FSE : Finite State Entropy codec + * Public Prototypes declaration + * Copyright (C) 2013-2016, Yann Collet. + * + * You can contact the author at : + * - Source repository : https://github.com/Cyan4973/FiniteStateEntropy + */ +#ifndef FSE_H +#define FSE_H + +/*-***************************************** +* Dependencies +******************************************/ +#include <linux/types.h> /* size_t, ptrdiff_t */ + +/*-***************************************** +* FSE_PUBLIC_API : control library symbols visibility +******************************************/ +#define FSE_PUBLIC_API + +/*------ Version ------*/ +#define FSE_VERSION_MAJOR 0 +#define FSE_VERSION_MINOR 9 +#define FSE_VERSION_RELEASE 0 + +#define FSE_LIB_VERSION FSE_VERSION_MAJOR.FSE_VERSION_MINOR.FSE_VERSION_RELEASE +#define FSE_QUOTE(str) #str +#define FSE_EXPAND_AND_QUOTE(str) FSE_QUOTE(str) +#define FSE_VERSION_STRING FSE_EXPAND_AND_QUOTE(FSE_LIB_VERSION) + +#define FSE_VERSION_NUMBER (FSE_VERSION_MAJOR * 100 * 100 + FSE_VERSION_MINOR * 100 + FSE_VERSION_RELEASE) +FSE_PUBLIC_API unsigned FSE_versionNumber(void); /**< library version number; to be used when checking dll version */ + +/*-***************************************** +* Tool functions +******************************************/ +FSE_PUBLIC_API size_t FSE_compressBound(size_t size); /* maximum compressed size */ + +/* Error Management */ +FSE_PUBLIC_API unsigned FSE_isError(size_t code); /* tells if a return value is an error code */ + +/*-***************************************** +* FSE detailed API +******************************************/ +/*! +FSE_compress() does the following: +1. count symbol occurrence from source[] into table count[] +2. normalize counters so that sum(count[]) == Power_of_2 (2^tableLog) +3. save normalized counters to memory buffer using writeNCount() +4. build encoding table 'CTable' from normalized counters +5. encode the data stream using encoding table 'CTable' + +FSE_decompress() does the following: +1. read normalized counters with readNCount() +2. build decoding table 'DTable' from normalized counters +3. decode the data stream using decoding table 'DTable' + +The following API allows targeting specific sub-functions for advanced tasks. +For example, it's possible to compress several blocks using the same 'CTable', +or to save and provide normalized distribution using external method. +*/ + +/* *** COMPRESSION *** */ +/*! FSE_optimalTableLog(): + dynamically downsize 'tableLog' when conditions are met. + It saves CPU time, by using smaller tables, while preserving or even improving compression ratio. + @return : recommended tableLog (necessarily <= 'maxTableLog') */ +FSE_PUBLIC_API unsigned FSE_optimalTableLog(unsigned maxTableLog, size_t srcSize, unsigned maxSymbolValue); + +/*! FSE_normalizeCount(): + normalize counts so that sum(count[]) == Power_of_2 (2^tableLog) + 'normalizedCounter' is a table of short, of minimum size (maxSymbolValue+1). + @return : tableLog, + or an errorCode, which can be tested using FSE_isError() */ +FSE_PUBLIC_API size_t FSE_normalizeCount(short *normalizedCounter, unsigned tableLog, const unsigned *count, size_t srcSize, unsigned maxSymbolValue); + +/*! FSE_NCountWriteBound(): + Provides the maximum possible size of an FSE normalized table, given 'maxSymbolValue' and 'tableLog'. + Typically useful for allocation purpose. */ +FSE_PUBLIC_API size_t FSE_NCountWriteBound(unsigned maxSymbolValue, unsigned tableLog); + +/*! FSE_writeNCount(): + Compactly save 'normalizedCounter' into 'buffer'. + @return : size of the compressed table, + or an errorCode, which can be tested using FSE_isError(). */ +FSE_PUBLIC_API size_t FSE_writeNCount(void *buffer, size_t bufferSize, const short *normalizedCounter, unsigned maxSymbolValue, unsigned tableLog); + +/*! Constructor and Destructor of FSE_CTable. + Note that FSE_CTable size depends on 'tableLog' and 'maxSymbolValue' */ +typedef unsigned FSE_CTable; /* don't allocate that. It's only meant to be more restrictive than void* */ + +/*! FSE_compress_usingCTable(): + Compress `src` using `ct` into `dst` which must be already allocated. + @return : size of compressed data (<= `dstCapacity`), + or 0 if compressed data could not fit into `dst`, + or an errorCode, which can be tested using FSE_isError() */ +FSE_PUBLIC_API size_t FSE_compress_usingCTable(void *dst, size_t dstCapacity, const void *src, size_t srcSize, const FSE_CTable *ct); + +/*! +Tutorial : +---------- +The first step is to count all symbols. FSE_count() does this job very fast. +Result will be saved into 'count', a table of unsigned int, which must be already allocated, and have 'maxSymbolValuePtr[0]+1' cells. +'src' is a table of bytes of size 'srcSize'. All values within 'src' MUST be <= maxSymbolValuePtr[0] +maxSymbolValuePtr[0] will be updated, with its real value (necessarily <= original value) +FSE_count() will return the number of occurrence of the most frequent symbol. +This can be used to know if there is a single symbol within 'src', and to quickly evaluate its compressibility. +If there is an error, the function will return an ErrorCode (which can be tested using FSE_isError()). + +The next step is to normalize the frequencies. +FSE_normalizeCount() will ensure that sum of frequencies is == 2 ^'tableLog'. +It also guarantees a minimum of 1 to any Symbol with frequency >= 1. +You can use 'tableLog'==0 to mean "use default tableLog value". +If you are unsure of which tableLog value to use, you can ask FSE_optimalTableLog(), +which will provide the optimal valid tableLog given sourceSize, maxSymbolValue, and a user-defined maximum (0 means "default"). + +The result of FSE_normalizeCount() will be saved into a table, +called 'normalizedCounter', which is a table of signed short. +'normalizedCounter' must be already allocated, and have at least 'maxSymbolValue+1' cells. +The return value is tableLog if everything proceeded as expected. +It is 0 if there is a single symbol within distribution. +If there is an error (ex: invalid tableLog value), the function will return an ErrorCode (which can be tested using FSE_isError()). + +'normalizedCounter' can be saved in a compact manner to a memory area using FSE_writeNCount(). +'buffer' must be already allocated. +For guaranteed success, buffer size must be at least FSE_headerBound(). +The result of the function is the number of bytes written into 'buffer'. +If there is an error, the function will return an ErrorCode (which can be tested using FSE_isError(); ex : buffer size too small). + +'normalizedCounter' can then be used to create the compression table 'CTable'. +The space required by 'CTable' must be already allocated, using FSE_createCTable(). +You can then use FSE_buildCTable() to fill 'CTable'. +If there is an error, both functions will return an ErrorCode (which can be tested using FSE_isError()). + +'CTable' can then be used to compress 'src', with FSE_compress_usingCTable(). +Similar to FSE_count(), the convention is that 'src' is assumed to be a table of char of size 'srcSize' +The function returns the size of compressed data (without header), necessarily <= `dstCapacity`. +If it returns '0', compressed data could not fit into 'dst'. +If there is an error, the function will return an ErrorCode (which can be tested using FSE_isError()). +*/ + +/* *** DECOMPRESSION *** */ + +/*! FSE_readNCount(): + Read compactly saved 'normalizedCounter' from 'rBuffer'. + @return : size read from 'rBuffer', + or an errorCode, which can be tested using FSE_isError(). + maxSymbolValuePtr[0] and tableLogPtr[0] will also be updated with their respective values */ +FSE_PUBLIC_API size_t FSE_readNCount(short *normalizedCounter, unsigned *maxSymbolValuePtr, unsigned *tableLogPtr, const void *rBuffer, size_t rBuffSize); + +/*! Constructor and Destructor of FSE_DTable. + Note that its size depends on 'tableLog' */ +typedef unsigned FSE_DTable; /* don't allocate that. It's just a way to be more restrictive than void* */ + +/*! FSE_buildDTable(): + Builds 'dt', which must be already allocated, using FSE_createDTable(). + return : 0, or an errorCode, which can be tested using FSE_isError() */ +FSE_PUBLIC_API size_t FSE_buildDTable_wksp(FSE_DTable *dt, const short *normalizedCounter, unsigned maxSymbolValue, unsigned tableLog, void *workspace, size_t workspaceSize); + +/*! FSE_decompress_usingDTable(): + Decompress compressed source `cSrc` of size `cSrcSize` using `dt` + into `dst` which must be already allocated. + @return : size of regenerated data (necessarily <= `dstCapacity`), + or an errorCode, which can be tested using FSE_isError() */ +FSE_PUBLIC_API size_t FSE_decompress_usingDTable(void *dst, size_t dstCapacity, const void *cSrc, size_t cSrcSize, const FSE_DTable *dt); + +/*! +Tutorial : +---------- +(Note : these functions only decompress FSE-compressed blocks. + If block is uncompressed, use memcpy() instead + If block is a single repeated byte, use memset() instead ) + +The first step is to obtain the normalized frequencies of symbols. +This can be performed by FSE_readNCount() if it was saved using FSE_writeNCount(). +'normalizedCounter' must be already allocated, and have at least 'maxSymbolValuePtr[0]+1' cells of signed short. +In practice, that means it's necessary to know 'maxSymbolValue' beforehand, +or size the table to handle worst case situations (typically 256). +FSE_readNCount() will provide 'tableLog' and 'maxSymbolValue'. +The result of FSE_readNCount() is the number of bytes read from 'rBuffer'. +Note that 'rBufferSize' must be at least 4 bytes, even if useful information is less than that. +If there is an error, the function will return an error code, which can be tested using FSE_isError(). + +The next step is to build the decompression tables 'FSE_DTable' from 'normalizedCounter'. +This is performed by the function FSE_buildDTable(). +The space required by 'FSE_DTable' must be already allocated using FSE_createDTable(). +If there is an error, the function will return an error code, which can be tested using FSE_isError(). + +`FSE_DTable` can then be used to decompress `cSrc`, with FSE_decompress_usingDTable(). +`cSrcSize` must be strictly correct, otherwise decompression will fail. +FSE_decompress_usingDTable() result will tell how many bytes were regenerated (<=`dstCapacity`). +If there is an error, the function will return an error code, which can be tested using FSE_isError(). (ex: dst buffer too small) +*/ + +/* *** Dependency *** */ +#include "bitstream.h" + +/* ***************************************** +* Static allocation +*******************************************/ +/* FSE buffer bounds */ +#define FSE_NCOUNTBOUND 512 +#define FSE_BLOCKBOUND(size) (size + (size >> 7)) +#define FSE_COMPRESSBOUND(size) (FSE_NCOUNTBOUND + FSE_BLOCKBOUND(size)) /* Macro version, useful for static allocation */ + +/* It is possible to statically allocate FSE CTable/DTable as a table of FSE_CTable/FSE_DTable using below macros */ +#define FSE_CTABLE_SIZE_U32(maxTableLog, maxSymbolValue) (1 + (1 << (maxTableLog - 1)) + ((maxSymbolValue + 1) * 2)) +#define FSE_DTABLE_SIZE_U32(maxTableLog) (1 + (1 << maxTableLog)) + +/* ***************************************** +* FSE advanced API +*******************************************/ +/* FSE_count_wksp() : + * Same as FSE_count(), but using an externally provided scratch buffer. + * `workSpace` size must be table of >= `1024` unsigned + */ +size_t FSE_count_wksp(unsigned *count, unsigned *maxSymbolValuePtr, const void *source, size_t sourceSize, unsigned *workSpace); + +/* FSE_countFast_wksp() : + * Same as FSE_countFast(), but using an externally provided scratch buffer. + * `workSpace` must be a table of minimum `1024` unsigned + */ +size_t FSE_countFast_wksp(unsigned *count, unsigned *maxSymbolValuePtr, const void *src, size_t srcSize, unsigned *workSpace); + +/*! FSE_count_simple + * Same as FSE_countFast(), but does not use any additional memory (not even on stack). + * This function is unsafe, and will segfault if any value within `src` is `> *maxSymbolValuePtr` (presuming it's also the size of `count`). +*/ +size_t FSE_count_simple(unsigned *count, unsigned *maxSymbolValuePtr, const void *src, size_t srcSize); + +unsigned FSE_optimalTableLog_internal(unsigned maxTableLog, size_t srcSize, unsigned maxSymbolValue, unsigned minus); +/**< same as FSE_optimalTableLog(), which used `minus==2` */ + +size_t FSE_buildCTable_raw(FSE_CTable *ct, unsigned nbBits); +/**< build a fake FSE_CTable, designed for a flat distribution, where each symbol uses nbBits */ + +size_t FSE_buildCTable_rle(FSE_CTable *ct, unsigned char symbolValue); +/**< build a fake FSE_CTable, designed to compress always the same symbolValue */ + +/* FSE_buildCTable_wksp() : + * Same as FSE_buildCTable(), but using an externally allocated scratch buffer (`workSpace`). + * `wkspSize` must be >= `(1<<tableLog)`. + */ +size_t FSE_buildCTable_wksp(FSE_CTable *ct, const short *normalizedCounter, unsigned maxSymbolValue, unsigned tableLog, void *workSpace, size_t wkspSize); + +size_t FSE_buildDTable_raw(FSE_DTable *dt, unsigned nbBits); +/**< build a fake FSE_DTable, designed to read a flat distribution where each symbol uses nbBits */ + +size_t FSE_buildDTable_rle(FSE_DTable *dt, unsigned char symbolValue); +/**< build a fake FSE_DTable, designed to always generate the same symbolValue */ + +size_t FSE_decompress_wksp(void *dst, size_t dstCapacity, const void *cSrc, size_t cSrcSize, unsigned maxLog, void *workspace, size_t workspaceSize); +/**< same as FSE_decompress(), using an externally allocated `workSpace` produced with `FSE_DTABLE_SIZE_U32(maxLog)` */ + +/* ***************************************** +* FSE symbol compression API +*******************************************/ +/*! + This API consists of small unitary functions, which highly benefit from being inlined. + Hence their body are included in next section. +*/ +typedef struct { + ptrdiff_t value; + const void *stateTable; + const void *symbolTT; + unsigned stateLog; +} FSE_CState_t; + +static void FSE_initCState(FSE_CState_t *CStatePtr, const FSE_CTable *ct); + +static void FSE_encodeSymbol(BIT_CStream_t *bitC, FSE_CState_t *CStatePtr, unsigned symbol); + +static void FSE_flushCState(BIT_CStream_t *bitC, const FSE_CState_t *CStatePtr); + +/**< +These functions are inner components of FSE_compress_usingCTable(). +They allow the creation of custom streams, mixing multiple tables and bit sources. + +A key property to keep in mind is that encoding and decoding are done **in reverse direction**. +So the first symbol you will encode is the last you will decode, like a LIFO stack. + +You will need a few variables to track your CStream. They are : + +FSE_CTable ct; // Provided by FSE_buildCTable() +BIT_CStream_t bitStream; // bitStream tracking structure +FSE_CState_t state; // State tracking structure (can have several) + + +The first thing to do is to init bitStream and state. + size_t errorCode = BIT_initCStream(&bitStream, dstBuffer, maxDstSize); + FSE_initCState(&state, ct); + +Note that BIT_initCStream() can produce an error code, so its result should be tested, using FSE_isError(); +You can then encode your input data, byte after byte. +FSE_encodeSymbol() outputs a maximum of 'tableLog' bits at a time. +Remember decoding will be done in reverse direction. + FSE_encodeByte(&bitStream, &state, symbol); + +At any time, you can also add any bit sequence. +Note : maximum allowed nbBits is 25, for compatibility with 32-bits decoders + BIT_addBits(&bitStream, bitField, nbBits); + +The above methods don't commit data to memory, they just store it into local register, for speed. +Local register size is 64-bits on 64-bits systems, 32-bits on 32-bits systems (size_t). +Writing data to memory is a manual operation, performed by the flushBits function. + BIT_flushBits(&bitStream); + +Your last FSE encoding operation shall be to flush your last state value(s). + FSE_flushState(&bitStream, &state); + +Finally, you must close the bitStream. +The function returns the size of CStream in bytes. +If data couldn't fit into dstBuffer, it will return a 0 ( == not compressible) +If there is an error, it returns an errorCode (which can be tested using FSE_isError()). + size_t size = BIT_closeCStream(&bitStream); +*/ + +/* ***************************************** +* FSE symbol decompression API +*******************************************/ +typedef struct { + size_t state; + const void *table; /* precise table may vary, depending on U16 */ +} FSE_DState_t; + +static void FSE_initDState(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD, const FSE_DTable *dt); + +static unsigned char FSE_decodeSymbol(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD); + +static unsigned FSE_endOfDState(const FSE_DState_t *DStatePtr); + +/**< +Let's now decompose FSE_decompress_usingDTable() into its unitary components. +You will decode FSE-encoded symbols from the bitStream, +and also any other bitFields you put in, **in reverse order**. + +You will need a few variables to track your bitStream. They are : + +BIT_DStream_t DStream; // Stream context +FSE_DState_t DState; // State context. Multiple ones are possible +FSE_DTable* DTablePtr; // Decoding table, provided by FSE_buildDTable() + +The first thing to do is to init the bitStream. + errorCode = BIT_initDStream(&DStream, srcBuffer, srcSize); + +You should then retrieve your initial state(s) +(in reverse flushing order if you have several ones) : + errorCode = FSE_initDState(&DState, &DStream, DTablePtr); + +You can then decode your data, symbol after symbol. +For information the maximum number of bits read by FSE_decodeSymbol() is 'tableLog'. +Keep in mind that symbols are decoded in reverse order, like a LIFO stack (last in, first out). + unsigned char symbol = FSE_decodeSymbol(&DState, &DStream); + +You can retrieve any bitfield you eventually stored into the bitStream (in reverse order) +Note : maximum allowed nbBits is 25, for 32-bits compatibility + size_t bitField = BIT_readBits(&DStream, nbBits); + +All above operations only read from local register (which size depends on size_t). +Refueling the register from memory is manually performed by the reload method. + endSignal = FSE_reloadDStream(&DStream); + +BIT_reloadDStream() result tells if there is still some more data to read from DStream. +BIT_DStream_unfinished : there is still some data left into the DStream. +BIT_DStream_endOfBuffer : Dstream reached end of buffer. Its container may no longer be completely filled. +BIT_DStream_completed : Dstream reached its exact end, corresponding in general to decompression completed. +BIT_DStream_tooFar : Dstream went too far. Decompression result is corrupted. + +When reaching end of buffer (BIT_DStream_endOfBuffer), progress slowly, notably if you decode multiple symbols per loop, +to properly detect the exact end of stream. +After each decoded symbol, check if DStream is fully consumed using this simple test : + BIT_reloadDStream(&DStream) >= BIT_DStream_completed + +When it's done, verify decompression is fully completed, by checking both DStream and the relevant states. +Checking if DStream has reached its end is performed by : + BIT_endOfDStream(&DStream); +Check also the states. There might be some symbols left there, if some high probability ones (>50%) are possible. + FSE_endOfDState(&DState); +*/ + +/* ***************************************** +* FSE unsafe API +*******************************************/ +static unsigned char FSE_decodeSymbolFast(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD); +/* faster, but works only if nbBits is always >= 1 (otherwise, result will be corrupted) */ + +/* ***************************************** +* Implementation of inlined functions +*******************************************/ +typedef struct { + int deltaFindState; + U32 deltaNbBits; +} FSE_symbolCompressionTransform; /* total 8 bytes */ + +ZSTD_STATIC void FSE_initCState(FSE_CState_t *statePtr, const FSE_CTable *ct) +{ + const void *ptr = ct; + const U16 *u16ptr = (const U16 *)ptr; + const U32 tableLog = ZSTD_read16(ptr); + statePtr->value = (ptrdiff_t)1 << tableLog; + statePtr->stateTable = u16ptr + 2; + statePtr->symbolTT = ((const U32 *)ct + 1 + (tableLog ? (1 << (tableLog - 1)) : 1)); + statePtr->stateLog = tableLog; +} + +/*! FSE_initCState2() : +* Same as FSE_initCState(), but the first symbol to include (which will be the last to be read) +* uses the smallest state value possible, saving the cost of this symbol */ +ZSTD_STATIC void FSE_initCState2(FSE_CState_t *statePtr, const FSE_CTable *ct, U32 symbol) +{ + FSE_initCState(statePtr, ct); + { + const FSE_symbolCompressionTransform symbolTT = ((const FSE_symbolCompressionTransform *)(statePtr->symbolTT))[symbol]; + const U16 *stateTable = (const U16 *)(statePtr->stateTable); + U32 nbBitsOut = (U32)((symbolTT.deltaNbBits + (1 << 15)) >> 16); + statePtr->value = (nbBitsOut << 16) - symbolTT.deltaNbBits; + statePtr->value = stateTable[(statePtr->value >> nbBitsOut) + symbolTT.deltaFindState]; + } +} + +ZSTD_STATIC void FSE_encodeSymbol(BIT_CStream_t *bitC, FSE_CState_t *statePtr, U32 symbol) +{ + const FSE_symbolCompressionTransform symbolTT = ((const FSE_symbolCompressionTransform *)(statePtr->symbolTT))[symbol]; + const U16 *const stateTable = (const U16 *)(statePtr->stateTable); + U32 nbBitsOut = (U32)((statePtr->value + symbolTT.deltaNbBits) >> 16); + BIT_addBits(bitC, statePtr->value, nbBitsOut); + statePtr->value = stateTable[(statePtr->value >> nbBitsOut) + symbolTT.deltaFindState]; +} + +ZSTD_STATIC void FSE_flushCState(BIT_CStream_t *bitC, const FSE_CState_t *statePtr) +{ + BIT_addBits(bitC, statePtr->value, statePtr->stateLog); + BIT_flushBits(bitC); +} + +/* ====== Decompression ====== */ + +typedef struct { + U16 tableLog; + U16 fastMode; +} FSE_DTableHeader; /* sizeof U32 */ + +typedef struct { + unsigned short newState; + unsigned char symbol; + unsigned char nbBits; +} FSE_decode_t; /* size == U32 */ + +ZSTD_STATIC void FSE_initDState(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD, const FSE_DTable *dt) +{ + const void *ptr = dt; + const FSE_DTableHeader *const DTableH = (const FSE_DTableHeader *)ptr; + DStatePtr->state = BIT_readBits(bitD, DTableH->tableLog); + BIT_reloadDStream(bitD); + DStatePtr->table = dt + 1; +} + +ZSTD_STATIC BYTE FSE_peekSymbol(const FSE_DState_t *DStatePtr) +{ + FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state]; + return DInfo.symbol; +} + +ZSTD_STATIC void FSE_updateState(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD) +{ + FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state]; + U32 const nbBits = DInfo.nbBits; + size_t const lowBits = BIT_readBits(bitD, nbBits); + DStatePtr->state = DInfo.newState + lowBits; +} + +ZSTD_STATIC BYTE FSE_decodeSymbol(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD) +{ + FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state]; + U32 const nbBits = DInfo.nbBits; + BYTE const symbol = DInfo.symbol; + size_t const lowBits = BIT_readBits(bitD, nbBits); + + DStatePtr->state = DInfo.newState + lowBits; + return symbol; +} + +/*! FSE_decodeSymbolFast() : + unsafe, only works if no symbol has a probability > 50% */ +ZSTD_STATIC BYTE FSE_decodeSymbolFast(FSE_DState_t *DStatePtr, BIT_DStream_t *bitD) +{ + FSE_decode_t const DInfo = ((const FSE_decode_t *)(DStatePtr->table))[DStatePtr->state]; + U32 const nbBits = DInfo.nbBits; + BYTE const symbol = DInfo.symbol; + size_t const lowBits = BIT_readBitsFast(bitD, nbBits); + + DStatePtr->state = DInfo.newState + lowBits; + return symbol; +} + +ZSTD_STATIC unsigned FSE_endOfDState(const FSE_DState_t *DStatePtr) { return DStatePtr->state == 0; } + +/* ************************************************************** +* Tuning parameters +****************************************************************/ +/*!MEMORY_USAGE : +* Memory usage formula : N->2^N Bytes (examples : 10 -> 1KB; 12 -> 4KB ; 16 -> 64KB; 20 -> 1MB; etc.) +* Increasing memory usage improves compression ratio +* Reduced memory usage can improve speed, due to cache effect +* Recommended max value is 14, for 16KB, which nicely fits into Intel x86 L1 cache */ +#ifndef FSE_MAX_MEMORY_USAGE +#define FSE_MAX_MEMORY_USAGE 14 +#endif +#ifndef FSE_DEFAULT_MEMORY_USAGE +#define FSE_DEFAULT_MEMORY_USAGE 13 +#endif + +/*!FSE_MAX_SYMBOL_VALUE : +* Maximum symbol value authorized. +* Required for proper stack allocation */ +#ifndef FSE_MAX_SYMBOL_VALUE +#define FSE_MAX_SYMBOL_VALUE 255 +#endif + +/* ************************************************************** +* template functions type & suffix +****************************************************************/ +#define FSE_FUNCTION_TYPE BYTE +#define FSE_FUNCTION_EXTENSION +#define FSE_DECODE_TYPE FSE_decode_t + +/* *************************************************************** +* Constants +*****************************************************************/ +#define FSE_MAX_TABLELOG (FSE_MAX_MEMORY_USAGE - 2) +#define FSE_MAX_TABLESIZE (1U << FSE_MAX_TABLELOG) +#define FSE_MAXTABLESIZE_MASK (FSE_MAX_TABLESIZE - 1) +#define FSE_DEFAULT_TABLELOG (FSE_DEFAULT_MEMORY_USAGE - 2) +#define FSE_MIN_TABLELOG 5 + +#define FSE_TABLELOG_ABSOLUTE_MAX 15 +#if FSE_MAX_TABLELOG > FSE_TABLELOG_ABSOLUTE_MAX +#error "FSE_MAX_TABLELOG > FSE_TABLELOG_ABSOLUTE_MAX is not supported" +#endif + +#define FSE_TABLESTEP(tableSize) ((tableSize >> 1) + (tableSize >> 3) + 3) + +#endif /* FSE_H */ |