| /* 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 "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); |
| } |
| } |