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      1 /* Ppmd7Dec.c -- PPMdH Decoder
      2 2010-03-12 : Igor Pavlov : Public domain
      3 This 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 
     11 Bool 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 
     23 static UInt32 Range_GetThreshold(void *pp, UInt32 total)
     24 {
     25   CPpmd7z_RangeDec *p = (CPpmd7z_RangeDec *)pp;
     26   return (p->Code) / (p->Range /= total);
     27 }
     28 
     29 static 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 
     43 static 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 
     51 static 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 
     71 void 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 
     81 int 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 }
    190