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1/* Ppmd8Dec.c -- PPMdI Decoder
2018-07-04 : 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)
BoolInt 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) | IByteIn_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) | IByteIn_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 iвв
UInt32 count, hiCnt;
if ((count = RangeDec_GetThreshold(p, p->MinContext->SummFreq)) < (hiCnt = s->Freq))
{
Byte symbol;
RangeDec_Decode(p, 0, s->Freq);dd
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);
}
}