Method decodeSymbol2

Libraries/unrar/model.cpp:490–547

inline bool RARPPM_CONTEXT::decodeSymbol2(ModelPPM *Model)
{
  int count, HiCnt, i=NumStats-Model->NumMasked;
  RARPPM_SEE2_CONTEXT* psee2c=makeEscFreq2(Model,i);
  RARPPM_STATE* ps[256], ** pps=ps, * p=U.Stats-1;
  HiCnt=0;
  do 
  {
    do 
    { 
      p++; 
    } while (Model->CharMask[p->Symbol] == Model->EscCount);
    HiCnt += p->Freq;

    // We do not reuse PPMd coder in unstable state, so we do not really need
    // this check and added it for extra safety. See CVE-2017-17969 for details.
    if (pps>=ps+ASIZE(ps))
      return false;

    *pps++ = p;
  } while ( --i );
  Model->Coder.SubRange.scale += HiCnt;
  count=Model->Coder.GetCurrentCount();
  if (count>=(int)Model->Coder.SubRange.scale)
    return(false);
  p=*(pps=ps);
  if (count < HiCnt) 
  {
    HiCnt=0;
    while ((HiCnt += p->Freq) <= count) 
    {
      pps++;
      if (pps>=ps+ASIZE(ps)) // Extra safety check.
        return false;
      p=*pps;
    }
    Model->Coder.SubRange.LowCount = (Model->Coder.SubRange.HighCount=HiCnt)-p->Freq;
    psee2c->update();
    update2(Model,p);
  }
  else
  {
    Model->Coder.SubRange.LowCount=HiCnt;
    Model->Coder.SubRange.HighCount=Model->Coder.SubRange.scale;
    i=NumStats-Model->NumMasked;
    pps--;
    do 
    { 
      pps++;
      if (pps>=ps+ASIZE(ps)) // Extra safety check.
        return false;
      Model->CharMask[(*pps)->Symbol]=Model->EscCount; 
    } while ( --i );
    psee2c->Summ += Model->Coder.SubRange.scale;
    Model->NumMasked = NumStats;
  }
  return true;
}