1/* Ppmd7Dec.c -- PPMdH Decoder
  22010-03-12 : Igor Pavlov : Public domain
  3This code is based on PPMd var.H (2001): Dmitry Shkarin : Public domain */
  4
  5#include "Precomp.h"
  6
  7#include "Ppmd7.h"
  8
  9#define kTopValue (1 << 24)
 10
 11Bool Ppmd7z_RangeDec_Init(CPpmd7z_RangeDec *p)
 12{
 13  unsigned i;
 14  p->Code = 0;
 15  p->Range = 0xFFFFFFFF;
 16  if (p->Stream->Read((void *)p->Stream) != 0)
 17    return False;
 18  for (i = 0; i < 4; i++)
 19    p->Code = (p->Code << 8) | p->Stream->Read((void *)p->Stream);
 20  return (p->Code < 0xFFFFFFFF);
 21}
 22
 23static UInt32 Range_GetThreshold(void *pp, UInt32 total)
 24{
 25  CPpmd7z_RangeDec *p = (CPpmd7z_RangeDec *)pp;
 26  return (p->Code) / (p->Range /= total);
 27}
 28
 29static void Range_Normalize(CPpmd7z_RangeDec *p)
 30{
 31  if (p->Range < kTopValue)
 32  {
 33    p->Code = (p->Code << 8) | p->Stream->Read((void *)p->Stream);
 34    p->Range <<= 8;
 35    if (p->Range < kTopValue)
 36    {
 37      p->Code = (p->Code << 8) | p->Stream->Read((void *)p->Stream);
 38      p->Range <<= 8;
 39    }
 40  }
 41}
 42
 43static void Range_Decode(void *pp, UInt32 start, UInt32 size)
 44{
 45  CPpmd7z_RangeDec *p = (CPpmd7z_RangeDec *)pp;
 46  p->Code -= start * p->Range;
 47  p->Range *= size;
 48  Range_Normalize(p);
 49}
 50
 51static UInt32 Range_DecodeBit(void *pp, UInt32 size0)
 52{
 53  CPpmd7z_RangeDec *p = (CPpmd7z_RangeDec *)pp;
 54  UInt32 newBound = (p->Range >> 14) * size0;
 55  UInt32 symbol;
 56  if (p->Code < newBound)
 57  {
 58    symbol = 0;
 59    p->Range = newBound;
 60  }
 61  else
 62  {
 63    symbol = 1;
 64    p->Code -= newBound;
 65    p->Range -= newBound;
 66  }
 67  Range_Normalize(p);
 68  return symbol;
 69}
 70
 71void Ppmd7z_RangeDec_CreateVTable(CPpmd7z_RangeDec *p)
 72{
 73  p->p.GetThreshold = Range_GetThreshold;
 74  p->p.Decode = Range_Decode;
 75  p->p.DecodeBit = Range_DecodeBit;
 76}
 77
 78
 79#define MASK(sym) ((signed char *)charMask)[sym]
 80
 81int Ppmd7_DecodeSymbol(CPpmd7 *p, IPpmd7_RangeDec *rc)
 82{
 83  size_t charMask[256 / sizeof(size_t)];
 84  if (p->MinContext->NumStats != 1)
 85  {
 86    CPpmd_State *s = Ppmd7_GetStats(p, p->MinContext);
 87    unsigned i;
 88    UInt32 count, hiCnt;
 89    if ((count = rc->GetThreshold(rc, p->MinContext->SummFreq)) < (hiCnt = s->Freq))
 90    {
 91      Byte symbol;
 92      rc->Decode(rc, 0, s->Freq);
 93      p->FoundState = s;
 94      symbol = s->Symbol;
 95      Ppmd7_Update1_0(p);
 96      return symbol;
 97    }
 98    p->PrevSuccess = 0;
 99    i = p->MinContext->NumStats - 1;
100    do
101    {
102      if ((hiCnt += (++s)->Freq) > count)
103      {
104        Byte symbol;
105        rc->Decode(rc, hiCnt - s->Freq, s->Freq);
106        p->FoundState = s;
107        symbol = s->Symbol;
108        Ppmd7_Update1(p);
109        return symbol;
110      }
111    }
112    while (--i);
113    if (count >= p->MinContext->SummFreq)
114      return -2;
115    p->HiBitsFlag = p->HB2Flag[p->FoundState->Symbol];
116    rc->Decode(rc, hiCnt, p->MinContext->SummFreq - hiCnt);
117    PPMD_SetAllBitsIn256Bytes(charMask);
118    MASK(s->Symbol) = 0;
119    i = p->MinContext->NumStats - 1;
120    do { MASK((--s)->Symbol) = 0; } while (--i);
121  }
122  else
123  {
124    UInt16 *prob = Ppmd7_GetBinSumm(p);
125    if (rc->DecodeBit(rc, *prob) == 0)
126    {
127      Byte symbol;
128      *prob = (UInt16)PPMD_UPDATE_PROB_0(*prob);
129      symbol = (p->FoundState = Ppmd7Context_OneState(p->MinContext))->Symbol;
130      Ppmd7_UpdateBin(p);
131      return symbol;
132    }
133    *prob = (UInt16)PPMD_UPDATE_PROB_1(*prob);
134    p->InitEsc = PPMD7_kExpEscape[*prob >> 10];
135    PPMD_SetAllBitsIn256Bytes(charMask);
136    MASK(Ppmd7Context_OneState(p->MinContext)->Symbol) = 0;
137    p->PrevSuccess = 0;
138  }
139  for (;;)
140  {
141    CPpmd_State *ps[256], *s;
142    UInt32 freqSum, count, hiCnt;
143    CPpmd_See *see;
144    unsigned i, num, numMasked = p->MinContext->NumStats;
145    do
146    {
147      p->OrderFall++;
148      if (!p->MinContext->Suffix)
149        return -1;
150      p->MinContext = Ppmd7_GetContext(p, p->MinContext->Suffix);
151    }
152    while (p->MinContext->NumStats == numMasked);
153    hiCnt = 0;
154    s = Ppmd7_GetStats(p, p->MinContext);
155    i = 0;
156    num = p->MinContext->NumStats - numMasked;
157    do
158    {
159      int k = (int)(MASK(s->Symbol));
160      hiCnt += (s->Freq & k);
161      ps[i] = s++;
162      i -= k;
163    }
164    while (i != num);
165    
166    see = Ppmd7_MakeEscFreq(p, numMasked, &freqSum);
167    freqSum += hiCnt;
168    count = rc->GetThreshold(rc, freqSum);
169    
170    if (count < hiCnt)
171    {
172      Byte symbol;
173      CPpmd_State **pps = ps;
174      for (hiCnt = 0; (hiCnt += (*pps)->Freq) <= count; pps++);
175      s = *pps;
176      rc->Decode(rc, hiCnt - s->Freq, s->Freq);
177      Ppmd_See_Update(see);
178      p->FoundState = s;
179      symbol = s->Symbol;
180      Ppmd7_Update2(p);
181      return symbol;
182    }
183    if (count >= freqSum)
184      return -2;
185    rc->Decode(rc, hiCnt, freqSum - hiCnt);
186    see->Summ = (UInt16)(see->Summ + freqSum);
187    do { MASK(ps[--i]->Symbol) = 0; } while (i != 0);
188  }
189}