1 // Compress/RangeCoder/RangeCoderBit.h

     2 

     3 #ifndef __COMPRESS_RANGECODER_BIT_H

     4 #define __COMPRESS_RANGECODER_BIT_H

     5 

     6 #include "RangeCoder.h"

     7 

     8 namespace NCompress {

     9 namespace NRangeCoder {

    10 

    11 const int kNumBitModelTotalBits  = 11;

    12 const UInt32 kBitModelTotal = (1 << kNumBitModelTotalBits);

    13 

    14 const int kNumMoveReducingBits = 2;

    15 

    16 const int kNumBitPriceShiftBits = 6;

    17 const UInt32 kBitPrice = 1 << kNumBitPriceShiftBits;

    18 

    19 class CPriceTables

    20 {

    21 public:

    22   static UInt32 ProbPrices[kBitModelTotal >> kNumMoveReducingBits];

    23   static void Init();

    24   CPriceTables();

    25 };

    26 

    27 template <int numMoveBits>

    28 class CBitModel

    29 {

    30 public:

    31   UInt32 Prob;

    32   void UpdateModel(UInt32 symbol)

    33   {

    34     /*

    35     Prob -= (Prob + ((symbol - 1) & ((1 << numMoveBits) - 1))) >> numMoveBits;

    36     Prob += (1 - symbol) << (kNumBitModelTotalBits - numMoveBits);

    37     */

    38     if (symbol == 0)

    39       Prob += (kBitModelTotal - Prob) >> numMoveBits;

    40     else

    41       Prob -= (Prob) >> numMoveBits;

    42   }

    43 public:

    44   void Init() { Prob = kBitModelTotal / 2; }

    45 };

    46 

    47 template <int numMoveBits>

    48 class CBitEncoder: public CBitModel<numMoveBits>

    49 {

    50 public:

    51   void Encode(CEncoder *encoder, UInt32 symbol)

    52   {

    53     /*

    54     encoder->EncodeBit(this->Prob, kNumBitModelTotalBits, symbol);

    55     this->UpdateModel(symbol);

    56     */

    57     UInt32 newBound = (encoder->Range >> kNumBitModelTotalBits) * this->Prob;

    58     if (symbol == 0)

    59     {

    60       encoder->Range = newBound;

    61       this->Prob += (kBitModelTotal - this->Prob) >> numMoveBits;

    62     }

    63     else

    64     {

    65       encoder->Low += newBound;

    66       encoder->Range -= newBound;

    67       this->Prob -= (this->Prob) >> numMoveBits;

    68     }

    69     if (encoder->Range < kTopValue)

    70     {

    71       encoder->Range <<= 8;

    72       encoder->ShiftLow();

    73     }

    74   }

    75   UInt32 GetPrice(UInt32 symbol) const

    76   {

    77     return CPriceTables::ProbPrices[

    78       (((this->Prob - symbol) ^ ((-(int)symbol))) & (kBitModelTotal - 1)) >> kNumMoveReducingBits];

    79   }

    80   UInt32 GetPrice0() const { return CPriceTables::ProbPrices[this->Prob >> kNumMoveReducingBits]; }

    81   UInt32 GetPrice1() const { return CPriceTables::ProbPrices[(kBitModelTotal - this->Prob) >> kNumMoveReducingBits]; }

    82 };

    83 

    84 

    85 template <int numMoveBits>

    86 class CBitDecoder: public CBitModel<numMoveBits>

    87 {

    88 public:

    89   UInt32 Decode(CDecoder *decoder)

    90   {

    91     UInt32 newBound = (decoder->Range >> kNumBitModelTotalBits) * this->Prob;

    92     if (decoder->Code < newBound)

    93     {

    94       decoder->Range = newBound;

    95       this->Prob += (kBitModelTotal - this->Prob) >> numMoveBits;

    96       if (decoder->Range < kTopValue)

    97       {

    98         decoder->Code = (decoder->Code << 8) | decoder->Stream.ReadByte();

    99         decoder->Range <<= 8;

   100       }

   101       return 0;

   102     }

   103     else

   104     {

   105       decoder->Range -= newBound;

   106       decoder->Code -= newBound;

   107       this->Prob -= (this->Prob) >> numMoveBits;

   108       if (decoder->Range < kTopValue)

   109       {

   110         decoder->Code = (decoder->Code << 8) | decoder->Stream.ReadByte();

   111         decoder->Range <<= 8;

   112       }

   113       return 1;

   114     }

   115   }

   116 };

   117 

   118 }}

   119 

   120 #endif