File indexing completed on 2025-02-02 04:26:00

 /* Ppmd8Dec.c -- PPMdI Decoder
 2010-04-16 : Igor Pavlov : Public domain
 This code is based on:
   PPMd var.I (2002): Dmitry Shkarin : Public domain
   Carryless rangecoder (1999): Dmitry Subbotin : Public domain */
 
 #include "Precomp.h"
 
 #include "Ppmd8.h"
 
 #define kTop (1 << 24)
 #define kBot (1 << 15)
 
 Bool Ppmd8_RangeDec_Init(CPpmd8 *p)
 {
   unsigned i;
   p->Low = 0;
   p->Range = 0xFFFFFFFF;
   p->Code = 0;
   for (i = 0; i < 4; i++)
     p->Code = (p->Code << 8) | p->Stream.In->Read(p->Stream.In);
   return (p->Code < 0xFFFFFFFF);
 }
 
 static UInt32 RangeDec_GetThreshold(CPpmd8 *p, UInt32 total)
 {
   return p->Code / (p->Range /= total);
 }
 
 static void RangeDec_Decode(CPpmd8 *p, UInt32 start, UInt32 size)
 {
   start *= p->Range;
   p->Low += start;
   p->Code -= start;
   p->Range *= size;
 
   while ((p->Low ^ (p->Low + p->Range)) < kTop ||
       (p->Range < kBot && ((p->Range = (0 - p->Low) & (kBot - 1)), 1)))
   {
     p->Code = (p->Code << 8) | p->Stream.In->Read(p->Stream.In);
     p->Range <<= 8;
     p->Low <<= 8;
   }
 }
 
 #define MASK(sym) ((signed char *)charMask)[sym]
 
 int Ppmd8_DecodeSymbol(CPpmd8 *p)
 {
   size_t charMask[256 / sizeof(size_t)];
   if (p->MinContext->NumStats != 0)
   {
     CPpmd_State *s = Ppmd8_GetStats(p, p->MinContext);
     unsigned i;
     UInt32 count, hiCnt;
     if ((count = RangeDec_GetThreshold(p, p->MinContext->SummFreq)) < (hiCnt = s->Freq))
     {
       Byte symbol;
       RangeDec_Decode(p, 0, s->Freq);
       p->FoundState = s;
       symbol = s->Symbol;
       Ppmd8_Update1_0(p);
       return symbol;
     }
     p->PrevSuccess = 0;
     i = p->MinContext->NumStats;
     do
     {
       if ((hiCnt += (++s)->Freq) > count)
       {
         Byte symbol;
         RangeDec_Decode(p, hiCnt - s->Freq, s->Freq);
         p->FoundState = s;
         symbol = s->Symbol;
         Ppmd8_Update1(p);
         return symbol;
       }
     }
     while (--i);
     if (count >= p->MinContext->SummFreq)
       return -2;
     RangeDec_Decode(p, hiCnt, p->MinContext->SummFreq - hiCnt);
     PPMD_SetAllBitsIn256Bytes(charMask);
     MASK(s->Symbol) = 0;
     i = p->MinContext->NumStats;
     do { MASK((--s)->Symbol) = 0; } while (--i);
   }
   else
   {
     UInt16 *prob = Ppmd8_GetBinSumm(p);
     if (((p->Code / (p->Range >>= 14)) < *prob))
     {
       Byte symbol;
       RangeDec_Decode(p, 0, *prob);
       *prob = (UInt16)PPMD_UPDATE_PROB_0(*prob);
       symbol = (p->FoundState = Ppmd8Context_OneState(p->MinContext))->Symbol;
       Ppmd8_UpdateBin(p);
       return symbol;
     }
     RangeDec_Decode(p, *prob, (1 << 14) - *prob);
     *prob = (UInt16)PPMD_UPDATE_PROB_1(*prob);
     p->InitEsc = PPMD8_kExpEscape[*prob >> 10];
     PPMD_SetAllBitsIn256Bytes(charMask);
     MASK(Ppmd8Context_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 = Ppmd8_GetContext(p, p->MinContext->Suffix);
     }
     while (p->MinContext->NumStats == numMasked);
     hiCnt = 0;
     s = Ppmd8_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 = Ppmd8_MakeEscFreq(p, numMasked, &freqSum);
     freqSum += hiCnt;
     count = RangeDec_GetThreshold(p, freqSum);
     
     if (count < hiCnt)
     {
       Byte symbol;
       CPpmd_State **pps = ps;
       for (hiCnt = 0; (hiCnt += (*pps)->Freq) <= count; pps++);
       s = *pps;
       RangeDec_Decode(p, hiCnt - s->Freq, s->Freq);
       Ppmd_See_Update(see);
       p->FoundState = s;
       symbol = s->Symbol;
       Ppmd8_Update2(p);
       return symbol;
     }
     if (count >= freqSum)
       return -2;
     RangeDec_Decode(p, hiCnt, freqSum - hiCnt);
     see->Summ = (UInt16)(see->Summ + freqSum);
     do { MASK(ps[--i]->Symbol) = 0; } while (i != 0);
   }
 }