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1 // Compress/RangeCoderBit.h
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2
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3 #ifndef __COMPRESS_RANGE_CODER_BIT_H
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4 #define __COMPRESS_RANGE_CODER_BIT_H
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5
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6 #include "RangeCoder.h"
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7
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8 namespace NCompress {
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9 namespace NRangeCoder {
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10
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11 const int kNumBitModelTotalBits = 11;
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12 const UInt32 kBitModelTotal = (1 << kNumBitModelTotalBits);
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13
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14 const int kNumMoveReducingBits = 4;
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15
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16 const int kNumBitPriceShiftBits = 4;
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17 const UInt32 kBitPrice = 1 << kNumBitPriceShiftBits;
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18
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19 extern UInt32 ProbPrices[kBitModelTotal >> kNumMoveReducingBits];
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20
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21 template <int numMoveBits>
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22 class CBitModel
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23 {
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24 public:
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25 UInt32 Prob;
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26 void UpdateModel(UInt32 symbol)
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27 {
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28 /*
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29 Prob -= (Prob + ((symbol - 1) & ((1 << numMoveBits) - 1))) >> numMoveBits;
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30 Prob += (1 - symbol) << (kNumBitModelTotalBits - numMoveBits);
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31 */
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32 if (symbol == 0)
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33 Prob += (kBitModelTotal - Prob) >> numMoveBits;
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34 else
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35 Prob -= (Prob) >> numMoveBits;
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36 }
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37 public:
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38 void Init() { Prob = kBitModelTotal / 2; }
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39 };
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40
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41 template <int numMoveBits>
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42 class CBitEncoder: public CBitModel<numMoveBits>
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43 {
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44 public:
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45 void Encode(CEncoder *encoder, UInt32 symbol)
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46 {
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47 /*
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48 encoder->EncodeBit(this->Prob, kNumBitModelTotalBits, symbol);
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49 this->UpdateModel(symbol);
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50 */
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51 UInt32 newBound = (encoder->Range >> kNumBitModelTotalBits) * this->Prob;
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52 if (symbol == 0)
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53 {
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54 encoder->Range = newBound;
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55 this->Prob += (kBitModelTotal - this->Prob) >> numMoveBits;
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56 }
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57 else
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58 {
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59 encoder->Low += newBound;
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60 encoder->Range -= newBound;
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61 this->Prob -= (this->Prob) >> numMoveBits;
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62 }
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63 if (encoder->Range < kTopValue)
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64 {
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65 encoder->Range <<= 8;
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66 encoder->ShiftLow();
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67 }
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68 }
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69 UInt32 GetPrice(UInt32 symbol) const
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70 {
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71 return ProbPrices[(this->Prob ^ ((-(int)symbol)) & (kBitModelTotal - 1)) >> kNumMoveReducingBits];
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72 }
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73 UInt32 GetPrice0() const { return ProbPrices[this->Prob >> kNumMoveReducingBits]; }
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74 UInt32 GetPrice1() const { return ProbPrices[(this->Prob ^ (kBitModelTotal - 1)) >> kNumMoveReducingBits]; }
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75 };
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76
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77
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78 template <int numMoveBits>
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79 class CBitDecoder: public CBitModel<numMoveBits>
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80 {
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81 public:
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82 UInt32 Decode(CDecoder *decoder)
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83 {
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84 UInt32 newBound = (decoder->Range >> kNumBitModelTotalBits) * this->Prob;
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85 if (decoder->Code < newBound)
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86 {
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87 decoder->Range = newBound;
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88 this->Prob += (kBitModelTotal - this->Prob) >> numMoveBits;
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89 if (decoder->Range < kTopValue)
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90 {
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91 decoder->Code = (decoder->Code << 8) | decoder->Stream.ReadByte();
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92 decoder->Range <<= 8;
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93 }
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94 return 0;
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95 }
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96 else
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97 {
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98 decoder->Range -= newBound;
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99 decoder->Code -= newBound;
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100 this->Prob -= (this->Prob) >> numMoveBits;
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101 if (decoder->Range < kTopValue)
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102 {
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103 decoder->Code = (decoder->Code << 8) | decoder->Stream.ReadByte();
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104 decoder->Range <<= 8;
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105 }
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106 return 1;
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107 }
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108 }
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109 };
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110
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111 }}
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112
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113 #endif
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