/* Ppmd7Dec.c -- PPMdH Decoder

2018-07-04 : Igor Pavlov : Public domain

This code is based on PPMd var.H (2001): Dmitry Shkarin : Public domain */

#include "Precomp.h"

#include "Ppmd7.h"

#define kTopValue (1 << 24)

BoolInt Ppmd7z_RangeDec_Init(CPpmd7z_RangeDec *p)

{

  unsigned i;

  p->Code = 0;

  p->Range = 0xFFFFFFFF;

  if (IByteIn_Read(p->Stream) != 0)

    return False;

  for (i = 0; i < 4; i++)

    p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);

  return (p->Code < 0xFFFFFFFF);

}

#define GET_Ppmd7z_RangeDec CPpmd7z_RangeDec *p = CONTAINER_FROM_VTBL(pp, CPpmd7z_RangeDec, vt);

static UInt32 Range_GetThreshold(const IPpmd7_RangeDec *pp, UInt32 total)

{

  GET_Ppmd7z_RangeDec

  return p->Code / (p->Range /= total);

}

static void Range_Normalize(CPpmd7z_RangeDec *p)

{

  if (p->Range < kTopValue)

  {

    p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);

    p->Range <<= 8;

    if (p->Range < kTopValue)

    {

      p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);

      p->Range <<= 8;

    }

  }

}

static void Range_Decode(const IPpmd7_RangeDec *pp, UInt32 start, UInt32 size)

{

  GET_Ppmd7z_RangeDec

  p->Code -= start * p->Range;

  p->Range *= size;

  Range_Normalize(p);

}

static UInt32 Range_DecodeBit(const IPpmd7_RangeDec *pp, UInt32 size0)

{

  GET_Ppmd7z_RangeDec

  UInt32 newBound = (p->Range >> 14) * size0;

  UInt32 symbol;

  if (p->Code < newBound)

  {

    symbol = 0;

    p->Range = newBound;

  }

  else

  {

    symbol = 1;

    p->Code -= newBound;

    p->Range -= newBound;

  }

  Range_Normalize(p);

  return symbol;

}

void Ppmd7z_RangeDec_CreateVTable(CPpmd7z_RangeDec *p)

{

  p->vt.GetThreshold = Range_GetThreshold;

  p->vt.Decode = Range_Decode;

  p->vt.DecodeBit = Range_DecodeBit;

}

#define MASK(sym) ((signed char *)charMask)[sym]

int Ppmd7_DecodeSymbol(CPpmd7 *p, const IPpmd7_RangeDec *rc)

{

  size_t charMask[256 / sizeof(size_t)];

  if (p->MinContext->NumStats != 1)

  {

    CPpmd_State *s = Ppmd7_GetStats(p, p->MinContext);

    unsigned i;

    UInt32 count, hiCnt;

    if ((count = rc->GetThreshold(rc, p->MinContext->SummFreq)) < (hiCnt = s->Freq))

    {

      Byte symbol;

      rc->Decode(rc, 0, s->Freq);

      p->FoundState = s;

      symbol = s->Symbol;

      Ppmd7_Update1_0(p);

      return symbol;

    }

    p->PrevSuccess = 0;

    i = p->MinContext->NumStats - 1;

    do

    {

      if ((hiCnt += (++s)->Freq) > count)

      {

        Byte symbol;

        rc->Decode(rc, hiCnt - s->Freq, s->Freq);

        p->FoundState = s;

        symbol = s->Symbol;

        Ppmd7_Update1(p);

        return symbol;

      }

    }

    while (--i);

    if (count >= p->MinContext->SummFreq)

      return -2;

    p->HiBitsFlag = p->HB2Flag[p->FoundState->Symbol];

    rc->Decode(rc, hiCnt, p->MinContext->SummFreq - hiCnt);

    PPMD_SetAllBitsIn256Bytes(charMask);

    MASK(s->Symbol) = 0;

    i = p->MinContext->NumStats - 1;

    do { MASK((--s)->Symbol) = 0; } while (--i);

  }

  else

  {

    UInt16 *prob = Ppmd7_GetBinSumm(p);

    if (rc->DecodeBit(rc, *prob) == 0)

    {

      Byte symbol;

      *prob = (UInt16)PPMD_UPDATE_PROB_0(*prob);

      symbol = (p->FoundState = Ppmd7Context_OneState(p->MinContext))->Symbol;

      Ppmd7_UpdateBin(p);

      return symbol;

    }

    *prob = (UInt16)PPMD_UPDATE_PROB_1(*prob);

    p->InitEsc = PPMD7_kExpEscape[*prob >> 10];

    PPMD_SetAllBitsIn256Bytes(charMask);

    MASK(Ppmd7Context_OneState(p->MinContext)->Symbol) = 0;

    p->PrevSuccess = 0;

  }

  for (;;)

  {

    CPpmd_State *ps[256], *s;

    UInt32 freqSum, count, hiCnt;

    CPpmd_See *see;

    unsigned i, num, numMasked = p->MinContext->NumStats;

    do

    {

      p->OrderFall++;

      if (!p->MinContext->Suffix)

        return -1;

      p->MinContext = Ppmd7_GetContext(p, p->MinContext->Suffix);

    }

    while (p->MinContext->NumStats == numMasked);

    hiCnt = 0;

    s = Ppmd7_GetStats(p, p->MinContext);

    i = 0;

    num = p->MinContext->NumStats - numMasked;

    do

    {

      int k = (int)(MASK(s->Symbol));

      hiCnt += (s->Freq & k);

      ps[i] = s++;

      i -= k;

    }

    while (i != num);

    see = Ppmd7_MakeEscFreq(p, numMasked, &freqSum);

    freqSum += hiCnt;

    count = rc->GetThreshold(rc, freqSum);

    if (count < hiCnt)

    {

      Byte symbol;

      CPpmd_State **pps = ps;

      for (hiCnt = 0; (hiCnt += (*pps)->Freq) <= count; pps++);

      s = *pps;

      rc->Decode(rc, hiCnt - s->Freq, s->Freq);

      Ppmd_See_Update(see);

      p->FoundState = s;

      symbol = s->Symbol;

      Ppmd7_Update2(p);

      return symbol;

    }

    if (count >= freqSum)

      return -2;

    rc->Decode(rc, hiCnt, freqSum - hiCnt);

    see->Summ = (UInt16)(see->Summ + freqSum);

    do { MASK(ps[--i]->Symbol) = 0; } while (i != 0);

  }

}