nel/3rdparty/seven_zip/Ppmd7Dec.c

   1 /* Ppmd7Dec.c -- PPMdH Decoder
   2 2018-07-04 : 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 BoolInt Ppmd7z_RangeDec_Init(CPpmd7z_RangeDec *p)
  12 {
  13   unsigned i;
  14   p->Code = 0;
  15   p->Range = 0xFFFFFFFF;
  16   if (IByteIn_Read(p->Stream) != 0)
  17     return False;
  18   for (i = 0; i < 4; i++)
  19     p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);
  20   return (p->Code < 0xFFFFFFFF);
  21 }
  22
  23 #define GET_Ppmd7z_RangeDec CPpmd7z_RangeDec *p = CONTAINER_FROM_VTBL(pp, CPpmd7z_RangeDec, vt);
  24
  25 static UInt32 Range_GetThreshold(const IPpmd7_RangeDec *pp, UInt32 total)
  26 {
  27   GET_Ppmd7z_RangeDec
  28   return p->Code / (p->Range /= total);
  29 }
  30
  31 static void Range_Normalize(CPpmd7z_RangeDec *p)
  32 {
  33   if (p->Range < kTopValue)
  34   {
  35     p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);
  36     p->Range <<= 8;
  37     if (p->Range < kTopValue)
  38     {
  39       p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);
  40       p->Range <<= 8;
  41     }
  42   }
  43 }
  44
  45 static void Range_Decode(const IPpmd7_RangeDec *pp, UInt32 start, UInt32 size)
  46 {
  47   GET_Ppmd7z_RangeDec
  48   p->Code -= start * p->Range;
  49   p->Range *= size;
  50   Range_Normalize(p);
  51 }
  52
  53 static UInt32 Range_DecodeBit(const IPpmd7_RangeDec *pp, UInt32 size0)
  54 {
  55   GET_Ppmd7z_RangeDec
  56   UInt32 newBound = (p->Range >> 14) * size0;
  57   UInt32 symbol;
  58   if (p->Code < newBound)
  59   {
  60     symbol = 0;
  61     p->Range = newBound;
  62   }
  63   else
  64   {
  65     symbol = 1;
  66     p->Code -= newBound;
  67     p->Range -= newBound;
  68   }
  69   Range_Normalize(p);
  70   return symbol;
  71 }
  72
  73 void Ppmd7z_RangeDec_CreateVTable(CPpmd7z_RangeDec *p)
  74 {
  75   p->vt.GetThreshold = Range_GetThreshold;
  76   p->vt.Decode = Range_Decode;
  77   p->vt.DecodeBit = Range_DecodeBit;
  78 }
  79
  80
  81 #define MASK(sym) ((signed char *)charMask)[sym]
  82
  83 int Ppmd7_DecodeSymbol(CPpmd7 *p, const IPpmd7_RangeDec *rc)
  84 {
  85   size_t charMask[256 / sizeof(size_t)];
  86   if (p->MinContext->NumStats != 1)
  87   {
  88     CPpmd_State *s = Ppmd7_GetStats(p, p->MinContext);
  89     unsigned i;
  90     UInt32 count, hiCnt;
  91     if ((count = rc->GetThreshold(rc, p->MinContext->SummFreq)) < (hiCnt = s->Freq))
  92     {
  93       Byte symbol;
  94       rc->Decode(rc, 0, s->Freq);
  95       p->FoundState = s;
  96       symbol = s->Symbol;
  97       Ppmd7_Update1_0(p);
  98       return symbol;
  99     }
 100     p->PrevSuccess = 0;
 101     i = p->MinContext->NumStats - 1;
 102     do
 103     {
 104       if ((hiCnt += (++s)->Freq) > count)
 105       {
 106         Byte symbol;
 107         rc->Decode(rc, hiCnt - s->Freq, s->Freq);
 108         p->FoundState = s;
 109         symbol = s->Symbol;
 110         Ppmd7_Update1(p);
 111         return symbol;
 112       }
 113     }
 114     while (--i);
 115     if (count >= p->MinContext->SummFreq)
 116       return -2;
 117     p->HiBitsFlag = p->HB2Flag[p->FoundState->Symbol];
 118     rc->Decode(rc, hiCnt, p->MinContext->SummFreq - hiCnt);
 119     PPMD_SetAllBitsIn256Bytes(charMask);
 120     MASK(s->Symbol) = 0;
 121     i = p->MinContext->NumStats - 1;
 122     do { MASK((--s)->Symbol) = 0; } while (--i);
 123   }
 124   else
 125   {
 126     UInt16 *prob = Ppmd7_GetBinSumm(p);
 127     if (rc->DecodeBit(rc, *prob) == 0)
 128     {
 129       Byte symbol;
 130       *prob = (UInt16)PPMD_UPDATE_PROB_0(*prob);
 131       symbol = (p->FoundState = Ppmd7Context_OneState(p->MinContext))->Symbol;
 132       Ppmd7_UpdateBin(p);
 133       return symbol;
 134     }
 135     *prob = (UInt16)PPMD_UPDATE_PROB_1(*prob);
 136     p->InitEsc = PPMD7_kExpEscape[*prob >> 10];
 137     PPMD_SetAllBitsIn256Bytes(charMask);
 138     MASK(Ppmd7Context_OneState(p->MinContext)->Symbol) = 0;
 139     p->PrevSuccess = 0;
 140   }
 141   for (;;)
 142   {
 143     CPpmd_State *ps[256], *s;
 144     UInt32 freqSum, count, hiCnt;
 145     CPpmd_See *see;
 146     unsigned i, num, numMasked = p->MinContext->NumStats;
 147     do
 148     {
 149       p->OrderFall++;
 150       if (!p->MinContext->Suffix)
 151         return -1;
 152       p->MinContext = Ppmd7_GetContext(p, p->MinContext->Suffix);
 153     }
 154     while (p->MinContext->NumStats == numMasked);
 155     hiCnt = 0;
 156     s = Ppmd7_GetStats(p, p->MinContext);
 157     i = 0;
 158     num = p->MinContext->NumStats - numMasked;
 159     do
 160     {
 161       int k = (int)(MASK(s->Symbol));
 162       hiCnt += (s->Freq & k);
 163       ps[i] = s++;
 164       i -= k;
 165     }
 166     while (i != num);
 167
 168     see = Ppmd7_MakeEscFreq(p, numMasked, &freqSum);
 169     freqSum += hiCnt;
 170     count = rc->GetThreshold(rc, freqSum);
 171
 172     if (count < hiCnt)
 173     {
 174       Byte symbol;
 175       CPpmd_State **pps = ps;
 176       for (hiCnt = 0; (hiCnt += (*pps)->Freq) <= count; pps++);
 177       s = *pps;
 178       rc->Decode(rc, hiCnt - s->Freq, s->Freq);
 179       Ppmd_See_Update(see);
 180       p->FoundState = s;
 181       symbol = s->Symbol;
 182       Ppmd7_Update2(p);
 183       return symbol;
 184     }
 185     if (count >= freqSum)
 186       return -2;
 187     rc->Decode(rc, hiCnt, freqSum - hiCnt);
 188     see->Summ = (UInt16)(see->Summ + freqSum);
 189     do { MASK(ps[--i]->Symbol) = 0; } while (i != 0);
 190   }
 191 }