/* ******************************************************************

 * FSE : Finite State Entropy decoder

 * Copyright (c) Meta Platforms, Inc. and affiliates.

 *

 *  You can contact the author at :

 *  - FSE source repository : https://github.com/Cyan4973/FiniteStateEntropy

 *  - Public forum : https://groups.google.com/forum/#!forum/lz4c

 *

 * This source code is licensed under both the BSD-style license (found in the

 * LICENSE file in the root directory of this source tree) and the GPLv2 (found

 * in the COPYING file in the root directory of this source tree).

 * You may select, at your option, one of the above-listed licenses.

****************************************************************** */

/* **************************************************************

*  Includes

****************************************************************/

#include "debug.h"      /* assert */

#include "bitstream.h"

#include "compiler.h"

#define FSE_STATIC_LINKING_ONLY

#include "fse.h"

#include "error_private.h"

#include "zstd_deps.h"  /* ZSTD_memcpy */

#include "bits.h"       /* ZSTD_highbit32 */

/* **************************************************************

*  Error Management

****************************************************************/

#define FSE_isError ERR_isError

#define FSE_STATIC_ASSERT(c) DEBUG_STATIC_ASSERT(c)   /* use only *after* variable declarations */

/* **************************************************************

*  Templates

****************************************************************/

/*

  designed to be included

  for type-specific functions (template emulation in C)

  Objective is to write these functions only once, for improved maintenance

*/

/* safety checks */

#ifndef FSE_FUNCTION_EXTENSION

#  error "FSE_FUNCTION_EXTENSION must be defined"

#endif

#ifndef FSE_FUNCTION_TYPE

#  error "FSE_FUNCTION_TYPE must be defined"

#endif

/* Function names */

#define FSE_CAT(X,Y) X##Y

#define FSE_FUNCTION_NAME(X,Y) FSE_CAT(X,Y)

#define FSE_TYPE_NAME(X,Y) FSE_CAT(X,Y)

static size_t FSE_buildDTable_internal(FSE_DTable* dt, const short* normalizedCounter, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize)

{

    void* const tdPtr = dt+1;   /* because *dt is unsigned, 32-bits aligned on 32-bits */

    FSE_DECODE_TYPE* const tableDecode = (FSE_DECODE_TYPE*) (tdPtr);

    U16* symbolNext = (U16*)workSpace;

    BYTE* spread = (BYTE*)(symbolNext + maxSymbolValue + 1);

    U32 const maxSV1 = maxSymbolValue + 1;

    U32 const tableSize = 1 << tableLog;

    U32 highThreshold = tableSize-1;

    /* Sanity Checks */

    if (FSE_BUILD_DTABLE_WKSP_SIZE(tableLog, maxSymbolValue) > wkspSize) return ERROR(maxSymbolValue_tooLarge);

    if (maxSymbolValue > FSE_MAX_SYMBOL_VALUE) return ERROR(maxSymbolValue_tooLarge);

    if (tableLog > FSE_MAX_TABLELOG) return ERROR(tableLog_tooLarge);

    /* Init, lay down lowprob symbols */

    {   FSE_DTableHeader DTableH;

        DTableH.tableLog = (U16)tableLog;

        DTableH.fastMode = 1;

        {   S16 const largeLimit= (S16)(1 << (tableLog-1));

            U32 s;

            for (s=0; s<maxSV1; s++) {

                if (normalizedCounter[s]==-1) {

                    tableDecode[highThreshold--].symbol = (FSE_FUNCTION_TYPE)s;

                    symbolNext[s] = 1;

                } else {

                    if (normalizedCounter[s] >= largeLimit) DTableH.fastMode=0;

                    symbolNext[s] = (U16)normalizedCounter[s];

        }   }   }

        ZSTD_memcpy(dt, &DTableH, sizeof(DTableH));

    }

    /* Spread symbols */

    if (highThreshold == tableSize - 1) {

        size_t const tableMask = tableSize-1;

        size_t const step = FSE_TABLESTEP(tableSize);

        /* First lay down the symbols in order.

         * We use a uint64_t to lay down 8 bytes at a time. This reduces branch

         * misses since small blocks generally have small table logs, so nearly

         * all symbols have counts <= 8. We ensure we have 8 bytes at the end of

         * our buffer to handle the over-write.

         */

        {   U64 const add = 0x0101010101010101ull;

            size_t pos = 0;

            U64 sv = 0;

            U32 s;

            for (s=0; s<maxSV1; ++s, sv += add) {

                int i;

                int const n = normalizedCounter[s];

                MEM_write64(spread + pos, sv);

                for (i = 8; i < n; i += 8) {

                    MEM_write64(spread + pos + i, sv);

                }

                pos += (size_t)n;

        }   }

        /* Now we spread those positions across the table.

         * The benefit of doing it in two stages is that we avoid the

         * variable size inner loop, which caused lots of branch misses.

         * Now we can run through all the positions without any branch misses.

         * We unroll the loop twice, since that is what empirically worked best.

         */

        {

            size_t position = 0;

            size_t s;

            size_t const unroll = 2;

            assert(tableSize % unroll == 0); /* FSE_MIN_TABLELOG is 5 */

            for (s = 0; s < (size_t)tableSize; s += unroll) {

                size_t u;

                for (u = 0; u < unroll; ++u) {

                    size_t const uPosition = (position + (u * step)) & tableMask;

                    tableDecode[uPosition].symbol = spread[s + u];

                }

                position = (position + (unroll * step)) & tableMask;

            }

            assert(position == 0);

        }

    } else {

        U32 const tableMask = tableSize-1;

        U32 const step = FSE_TABLESTEP(tableSize);

        U32 s, position = 0;

        for (s=0; s<maxSV1; s++) {

            int i;

            for (i=0; i<normalizedCounter[s]; i++) {

                tableDecode[position].symbol = (FSE_FUNCTION_TYPE)s;

                position = (position + step) & tableMask;

                while (position > highThreshold) position = (position + step) & tableMask;   /* lowprob area */

        }   }

        if (position!=0) return ERROR(GENERIC);   /* position must reach all cells once, otherwise normalizedCounter is incorrect */

    }

    /* Build Decoding table */

    {   U32 u;

        for (u=0; u<tableSize; u++) {

            FSE_FUNCTION_TYPE const symbol = (FSE_FUNCTION_TYPE)(tableDecode[u].symbol);

            U32 const nextState = symbolNext[symbol]++;

            tableDecode[u].nbBits = (BYTE) (tableLog - ZSTD_highbit32(nextState) );

            tableDecode[u].newState = (U16) ( (nextState << tableDecode[u].nbBits) - tableSize);

    }   }

    return 0;

}

size_t FSE_buildDTable_wksp(FSE_DTable* dt, const short* normalizedCounter, unsigned maxSymbolValue, unsigned tableLog, void* workSpace, size_t wkspSize)

{

    return FSE_buildDTable_internal(dt, normalizedCounter, maxSymbolValue, tableLog, workSpace, wkspSize);

}

#ifndef FSE_COMMONDEFS_ONLY

/*-*******************************************************

*  Decompression (Byte symbols)

*********************************************************/

FORCE_INLINE_TEMPLATE size_t FSE_decompress_usingDTable_generic(

          void* dst, size_t maxDstSize,

    const void* cSrc, size_t cSrcSize,

    const FSE_DTable* dt, const unsigned fast)

{

    BYTE* const ostart = (BYTE*) dst;

    BYTE* op = ostart;

    BYTE* const omax = op + maxDstSize;

    BYTE* const olimit = omax-3;

    BIT_DStream_t bitD;

    FSE_DState_t state1;

    FSE_DState_t state2;

    /* Init */

    CHECK_F(BIT_initDStream(&bitD, cSrc, cSrcSize));

    FSE_initDState(&state1, &bitD, dt);

    FSE_initDState(&state2, &bitD, dt);

    RETURN_ERROR_IF(BIT_reloadDStream(&bitD)==BIT_DStream_overflow, corruption_detected, "");

#define FSE_GETSYMBOL(statePtr) fast ? FSE_decodeSymbolFast(statePtr, &bitD) : FSE_decodeSymbol(statePtr, &bitD)

    /* 4 symbols per loop */

    for ( ; (BIT_reloadDStream(&bitD)==BIT_DStream_unfinished) & (op<olimit) ; op+=4) {

        op[0] = FSE_GETSYMBOL(&state1);

        if (FSE_MAX_TABLELOG*2+7 > sizeof(bitD.bitContainer)*8)    /* This test must be static */

            BIT_reloadDStream(&bitD);

        op[1] = FSE_GETSYMBOL(&state2);

        if (FSE_MAX_TABLELOG*4+7 > sizeof(bitD.bitContainer)*8)    /* This test must be static */

            { if (BIT_reloadDStream(&bitD) > BIT_DStream_unfinished) { op+=2; break; } }

        op[2] = FSE_GETSYMBOL(&state1);

        if (FSE_MAX_TABLELOG*2+7 > sizeof(bitD.bitContainer)*8)    /* This test must be static */

            BIT_reloadDStream(&bitD);

        op[3] = FSE_GETSYMBOL(&state2);

    }

    /* tail */

    /* note : BIT_reloadDStream(&bitD) >= FSE_DStream_partiallyFilled; Ends at exactly BIT_DStream_completed */

    while (1) {

        if (op>(omax-2)) return ERROR(dstSize_tooSmall);

        *op++ = FSE_GETSYMBOL(&state1);

        if (BIT_reloadDStream(&bitD)==BIT_DStream_overflow) {

            *op++ = FSE_GETSYMBOL(&state2);

            break;

        }

        if (op>(omax-2)) return ERROR(dstSize_tooSmall);

        *op++ = FSE_GETSYMBOL(&state2);

        if (BIT_reloadDStream(&bitD)==BIT_DStream_overflow) {

            *op++ = FSE_GETSYMBOL(&state1);

            break;

    }   }

    assert(op >= ostart);

    return (size_t)(op-ostart);

}

typedef struct {

    short ncount[FSE_MAX_SYMBOL_VALUE + 1];

} FSE_DecompressWksp;

FORCE_INLINE_TEMPLATE size_t FSE_decompress_wksp_body(

        void* dst, size_t dstCapacity,

        const void* cSrc, size_t cSrcSize,

        unsigned maxLog, void* workSpace, size_t wkspSize,

        int bmi2)

{

    const BYTE* const istart = (const BYTE*)cSrc;

    const BYTE* ip = istart;

    unsigned tableLog;

    unsigned maxSymbolValue = FSE_MAX_SYMBOL_VALUE;

    FSE_DecompressWksp* const wksp = (FSE_DecompressWksp*)workSpace;

    size_t const dtablePos = sizeof(FSE_DecompressWksp) / sizeof(FSE_DTable);

    FSE_DTable* const dtable = (FSE_DTable*)workSpace + dtablePos;

    FSE_STATIC_ASSERT((FSE_MAX_SYMBOL_VALUE + 1) % 2 == 0);

    if (wkspSize < sizeof(*wksp)) return ERROR(GENERIC);

    /* correct offset to dtable depends on this property */

    FSE_STATIC_ASSERT(sizeof(FSE_DecompressWksp) % sizeof(FSE_DTable) == 0);

    /* normal FSE decoding mode */

    {   size_t const NCountLength =

            FSE_readNCount_bmi2(wksp->ncount, &maxSymbolValue, &tableLog, istart, cSrcSize, bmi2);

        if (FSE_isError(NCountLength)) return NCountLength;

        if (tableLog > maxLog) return ERROR(tableLog_tooLarge);

        assert(NCountLength <= cSrcSize);

        ip += NCountLength;

        cSrcSize -= NCountLength;

    }

    if (FSE_DECOMPRESS_WKSP_SIZE(tableLog, maxSymbolValue) > wkspSize) return ERROR(tableLog_tooLarge);

    assert(sizeof(*wksp) + FSE_DTABLE_SIZE(tableLog) <= wkspSize);

    workSpace = (BYTE*)workSpace + sizeof(*wksp) + FSE_DTABLE_SIZE(tableLog);

    wkspSize -= sizeof(*wksp) + FSE_DTABLE_SIZE(tableLog);

    CHECK_F( FSE_buildDTable_internal(dtable, wksp->ncount, maxSymbolValue, tableLog, workSpace, wkspSize) );

    {

        const void* ptr = dtable;

        const FSE_DTableHeader* DTableH = (const FSE_DTableHeader*)ptr;

        const U32 fastMode = DTableH->fastMode;

        /* select fast mode (static) */

        if (fastMode) return FSE_decompress_usingDTable_generic(dst, dstCapacity, ip, cSrcSize, dtable, 1);

        return FSE_decompress_usingDTable_generic(dst, dstCapacity, ip, cSrcSize, dtable, 0);

    }

}

/* Avoids the FORCE_INLINE of the _body() function. */

static size_t FSE_decompress_wksp_body_default(void* dst, size_t dstCapacity, const void* cSrc, size_t cSrcSize, unsigned maxLog, void* workSpace, size_t wkspSize)

{

    return FSE_decompress_wksp_body(dst, dstCapacity, cSrc, cSrcSize, maxLog, workSpace, wkspSize, 0);

}

#if DYNAMIC_BMI2

BMI2_TARGET_ATTRIBUTE static size_t FSE_decompress_wksp_body_bmi2(void* dst, size_t dstCapacity, const void* cSrc, size_t cSrcSize, unsigned maxLog, void* workSpace, size_t wkspSize)

{

    return FSE_decompress_wksp_body(dst, dstCapacity, cSrc, cSrcSize, maxLog, workSpace, wkspSize, 1);

}

#endif

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)

{

#if DYNAMIC_BMI2

    if (bmi2) {

        return FSE_decompress_wksp_body_bmi2(dst, dstCapacity, cSrc, cSrcSize, maxLog, workSpace, wkspSize);

    }

#endif

    (void)bmi2;

    return FSE_decompress_wksp_body_default(dst, dstCapacity, cSrc, cSrcSize, maxLog, workSpace, wkspSize);

}

#endif   /* FSE_COMMONDEFS_ONLY */