tor-browser

Ppmd7Dec.c (4921B)

---

/* Ppmd7Dec.c -- PPMdH Decoder
2017-04-03 : Igor Pavlov : Public domain
This code is based on PPMd var.H (2001): Dmitry Shkarin : Public domain */

#include "Precomp.h"

#include "Ppmd7.h"

#define kTopValue (1 << 24)

Bool Ppmd7z_RangeDec_Init(CPpmd7z_RangeDec *p)
{
 unsigned i;
 p->Code = 0;
 p->Range = 0xFFFFFFFF;
 if (IByteIn_Read(p->Stream) != 0)
   return False;
 for (i = 0; i < 4; i++)
   p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);
 return (p->Code < 0xFFFFFFFF);
}

#define GET_Ppmd7z_RangeDec CPpmd7z_RangeDec *p = CONTAINER_FROM_VTBL(pp, CPpmd7z_RangeDec, vt);

static UInt32 Range_GetThreshold(const IPpmd7_RangeDec *pp, UInt32 total)
{
 GET_Ppmd7z_RangeDec
 return p->Code / (p->Range /= total);
}

static void Range_Normalize(CPpmd7z_RangeDec *p)
{
 if (p->Range < kTopValue)
 {
   p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);
   p->Range <<= 8;
   if (p->Range < kTopValue)
   {
     p->Code = (p->Code << 8) | IByteIn_Read(p->Stream);
     p->Range <<= 8;
   }
 }
}

static void Range_Decode(const IPpmd7_RangeDec *pp, UInt32 start, UInt32 size)
{
 GET_Ppmd7z_RangeDec
 p->Code -= start * p->Range;
 p->Range *= size;
 Range_Normalize(p);
}

static UInt32 Range_DecodeBit(const IPpmd7_RangeDec *pp, UInt32 size0)
{
 GET_Ppmd7z_RangeDec
 UInt32 newBound = (p->Range >> 14) * size0;
 UInt32 symbol;
 if (p->Code < newBound)
 {
   symbol = 0;
   p->Range = newBound;
 }
 else
 {
   symbol = 1;
   p->Code -= newBound;
   p->Range -= newBound;
 }
 Range_Normalize(p);
 return symbol;
}

void Ppmd7z_RangeDec_CreateVTable(CPpmd7z_RangeDec *p)
{
 p->vt.GetThreshold = Range_GetThreshold;
 p->vt.Decode = Range_Decode;
 p->vt.DecodeBit = Range_DecodeBit;
}


#define MASK(sym) ((signed char *)charMask)[sym]

int Ppmd7_DecodeSymbol(CPpmd7 *p, const IPpmd7_RangeDec *rc)
{
 size_t charMask[256 / sizeof(size_t)];
 if (p->MinContext->NumStats != 1)
 {
   CPpmd_State *s = Ppmd7_GetStats(p, p->MinContext);
   unsigned i;
   UInt32 count, hiCnt;
   if ((count = rc->GetThreshold(rc, p->MinContext->SummFreq)) < (hiCnt = s->Freq))
   {
     Byte symbol;
     rc->Decode(rc, 0, s->Freq);
     p->FoundState = s;
     symbol = s->Symbol;
     Ppmd7_Update1_0(p);
     return symbol;
   }
   p->PrevSuccess = 0;
   i = p->MinContext->NumStats - 1;
   do
   {
     if ((hiCnt += (++s)->Freq) > count)
     {
       Byte symbol;
       rc->Decode(rc, hiCnt - s->Freq, s->Freq);
       p->FoundState = s;
       symbol = s->Symbol;
       Ppmd7_Update1(p);
       return symbol;
     }
   }
   while (--i);
   if (count >= p->MinContext->SummFreq)
     return -2;
   p->HiBitsFlag = p->HB2Flag[p->FoundState->Symbol];
   rc->Decode(rc, hiCnt, p->MinContext->SummFreq - hiCnt);
   PPMD_SetAllBitsIn256Bytes(charMask);
   MASK(s->Symbol) = 0;
   i = p->MinContext->NumStats - 1;
   do { MASK((--s)->Symbol) = 0; } while (--i);
 }
 else
 {
   UInt16 *prob = Ppmd7_GetBinSumm(p);
   if (rc->DecodeBit(rc, *prob) == 0)
   {
     Byte symbol;
     *prob = (UInt16)PPMD_UPDATE_PROB_0(*prob);
     symbol = (p->FoundState = Ppmd7Context_OneState(p->MinContext))->Symbol;
     Ppmd7_UpdateBin(p);
     return symbol;
   }
   *prob = (UInt16)PPMD_UPDATE_PROB_1(*prob);
   p->InitEsc = PPMD7_kExpEscape[*prob >> 10];
   PPMD_SetAllBitsIn256Bytes(charMask);
   MASK(Ppmd7Context_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 = Ppmd7_GetContext(p, p->MinContext->Suffix);
   }
   while (p->MinContext->NumStats == numMasked);
   hiCnt = 0;
   s = Ppmd7_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 = Ppmd7_MakeEscFreq(p, numMasked, &freqSum);
   freqSum += hiCnt;
   count = rc->GetThreshold(rc, freqSum);
   
   if (count < hiCnt)
   {
     Byte symbol;
     CPpmd_State **pps = ps;
     for (hiCnt = 0; (hiCnt += (*pps)->Freq) <= count; pps++);
     s = *pps;
     rc->Decode(rc, hiCnt - s->Freq, s->Freq);
     Ppmd_See_Update(see);
     p->FoundState = s;
     symbol = s->Symbol;
     Ppmd7_Update2(p);
     return symbol;
   }
   if (count >= freqSum)
     return -2;
   rc->Decode(rc, hiCnt, freqSum - hiCnt);
   see->Summ = (UInt16)(see->Summ + freqSum);
   do { MASK(ps[--i]->Symbol) = 0; } while (i != 0);
 }
}