1 /* Ppmd7Dec.c -- PPMdH Decoder
2 2010-03-12 : Igor Pavlov : Public domain
3 This code is based on PPMd var.H (2001): Dmitry Shkarin : Public domain */
4 
5 #include "Ppmd7.h"
6 
7 #define kTopValue (1 << 24)
8 
Ppmd7z_RangeDec_Init(CPpmd7z_RangeDec * p)9 Bool Ppmd7z_RangeDec_Init(CPpmd7z_RangeDec *p)
10 {
11   unsigned i;
12   p->Code = 0;
13   p->Range = 0xFFFFFFFF;
14   if (p->Stream->Read((void *)p->Stream) != 0)
15     return False;
16   for (i = 0; i < 4; i++)
17     p->Code = (p->Code << 8) | p->Stream->Read((void *)p->Stream);
18   return (p->Code < 0xFFFFFFFF);
19 }
20 
Range_GetThreshold(void * pp,UInt32 total)21 static UInt32 Range_GetThreshold(void *pp, UInt32 total)
22 {
23   CPpmd7z_RangeDec *p = (CPpmd7z_RangeDec *)pp;
24   return (p->Code) / (p->Range /= total);
25 }
26 
Range_Normalize(CPpmd7z_RangeDec * p)27 static void Range_Normalize(CPpmd7z_RangeDec *p)
28 {
29   if (p->Range < kTopValue)
30   {
31     p->Code = (p->Code << 8) | p->Stream->Read((void *)p->Stream);
32     p->Range <<= 8;
33     if (p->Range < kTopValue)
34     {
35       p->Code = (p->Code << 8) | p->Stream->Read((void *)p->Stream);
36       p->Range <<= 8;
37     }
38   }
39 }
40 
Range_Decode(void * pp,UInt32 start,UInt32 size)41 static void Range_Decode(void *pp, UInt32 start, UInt32 size)
42 {
43   CPpmd7z_RangeDec *p = (CPpmd7z_RangeDec *)pp;
44   p->Code -= start * p->Range;
45   p->Range *= size;
46   Range_Normalize(p);
47 }
48 
Range_DecodeBit(void * pp,UInt32 size0)49 static UInt32 Range_DecodeBit(void *pp, UInt32 size0)
50 {
51   CPpmd7z_RangeDec *p = (CPpmd7z_RangeDec *)pp;
52   UInt32 newBound = (p->Range >> 14) * size0;
53   UInt32 symbol;
54   if (p->Code < newBound)
55   {
56     symbol = 0;
57     p->Range = newBound;
58   }
59   else
60   {
61     symbol = 1;
62     p->Code -= newBound;
63     p->Range -= newBound;
64   }
65   Range_Normalize(p);
66   return symbol;
67 }
68 
Ppmd7z_RangeDec_CreateVTable(CPpmd7z_RangeDec * p)69 void Ppmd7z_RangeDec_CreateVTable(CPpmd7z_RangeDec *p)
70 {
71   p->p.GetThreshold = Range_GetThreshold;
72   p->p.Decode = Range_Decode;
73   p->p.DecodeBit = Range_DecodeBit;
74 }
75 
76 
77 #define MASK(sym) ((signed char *)charMask)[sym]
78 
Ppmd7_DecodeSymbol(CPpmd7 * p,IPpmd7_RangeDec * rc)79 int Ppmd7_DecodeSymbol(CPpmd7 *p, IPpmd7_RangeDec *rc)
80 {
81   size_t charMask[256 / sizeof(size_t)];
82   if (p->MinContext->NumStats != 1)
83   {
84     CPpmd_State *s = Ppmd7_GetStats(p, p->MinContext);
85     unsigned i;
86     UInt32 count, hiCnt;
87     if ((count = rc->GetThreshold(rc, p->MinContext->SummFreq)) < (hiCnt = s->Freq))
88     {
89       Byte symbol;
90       rc->Decode(rc, 0, s->Freq);
91       p->FoundState = s;
92       symbol = s->Symbol;
93       Ppmd7_Update1_0(p);
94       return symbol;
95     }
96     p->PrevSuccess = 0;
97     i = p->MinContext->NumStats - 1;
98     do
99     {
100       if ((hiCnt += (++s)->Freq) > count)
101       {
102         Byte symbol;
103         rc->Decode(rc, hiCnt - s->Freq, s->Freq);
104         p->FoundState = s;
105         symbol = s->Symbol;
106         Ppmd7_Update1(p);
107         return symbol;
108       }
109     }
110     while (--i);
111     if (count >= p->MinContext->SummFreq)
112       return -2;
113     p->HiBitsFlag = p->HB2Flag[p->FoundState->Symbol];
114     rc->Decode(rc, hiCnt, p->MinContext->SummFreq - hiCnt);
115     PPMD_SetAllBitsIn256Bytes(charMask);
116     MASK(s->Symbol) = 0;
117     i = p->MinContext->NumStats - 1;
118     do { MASK((--s)->Symbol) = 0; } while (--i);
119   }
120   else
121   {
122     UInt16 *prob = Ppmd7_GetBinSumm(p);
123     if (rc->DecodeBit(rc, *prob) == 0)
124     {
125       Byte symbol;
126       *prob = (UInt16)PPMD_UPDATE_PROB_0(*prob);
127       symbol = (p->FoundState = Ppmd7Context_OneState(p->MinContext))->Symbol;
128       Ppmd7_UpdateBin(p);
129       return symbol;
130     }
131     *prob = (UInt16)PPMD_UPDATE_PROB_1(*prob);
132     p->InitEsc = PPMD7_kExpEscape[*prob >> 10];
133     PPMD_SetAllBitsIn256Bytes(charMask);
134     MASK(Ppmd7Context_OneState(p->MinContext)->Symbol) = 0;
135     p->PrevSuccess = 0;
136   }
137   for (;;)
138   {
139     CPpmd_State *ps[256], *s;
140     UInt32 freqSum, count, hiCnt;
141     CPpmd_See *see;
142     unsigned i, num, numMasked = p->MinContext->NumStats;
143     do
144     {
145       p->OrderFall++;
146       if (!p->MinContext->Suffix)
147         return -1;
148       p->MinContext = Ppmd7_GetContext(p, p->MinContext->Suffix);
149     }
150     while (p->MinContext->NumStats == numMasked);
151     hiCnt = 0;
152     s = Ppmd7_GetStats(p, p->MinContext);
153     i = 0;
154     num = p->MinContext->NumStats - numMasked;
155     do
156     {
157       int k = (int)(MASK(s->Symbol));
158       hiCnt += (s->Freq & k);
159       ps[i] = s++;
160       i -= k;
161     }
162     while (i != num);
163 
164     see = Ppmd7_MakeEscFreq(p, numMasked, &freqSum);
165     freqSum += hiCnt;
166     count = rc->GetThreshold(rc, freqSum);
167 
168     if (count < hiCnt)
169     {
170       Byte symbol;
171       CPpmd_State **pps = ps;
172       for (hiCnt = 0; (hiCnt += (*pps)->Freq) <= count; pps++);
173       s = *pps;
174       rc->Decode(rc, hiCnt - s->Freq, s->Freq);
175       Ppmd_See_Update(see);
176       p->FoundState = s;
177       symbol = s->Symbol;
178       Ppmd7_Update2(p);
179       return symbol;
180     }
181     if (count >= freqSum)
182       return -2;
183     rc->Decode(rc, hiCnt, freqSum - hiCnt);
184     see->Summ = (UInt16)(see->Summ + freqSum);
185     do { MASK(ps[--i]->Symbol) = 0; } while (i != 0);
186   }
187 }
188