1 using System;

     2 

     3 namespace SevenZip.Compression.RangeCoder

     4 {

     5 	struct BitEncoder

     6 	{

     7 		public const int kNumBitModelTotalBits = 11;

     8 		public const uint kBitModelTotal = (1 << kNumBitModelTotalBits);

     9 		const int kNumMoveBits = 5;

    10 		const int kNumMoveReducingBits = 2;

    11 		public const int kNumBitPriceShiftBits = 6;

    12 

    13 		uint Prob;

    14 

    15 		public void Init() { Prob = kBitModelTotal >> 1; }

    16 

    17 		public void UpdateModel(uint symbol)

    18 		{

    19 			if (symbol == 0)

    20 				Prob += (kBitModelTotal - Prob) >> kNumMoveBits;

    21 			else

    22 				Prob -= (Prob) >> kNumMoveBits;

    23 		}

    24 

    25 		public void Encode(Encoder encoder, uint symbol)

    26 		{

    27 			// encoder.EncodeBit(Prob, kNumBitModelTotalBits, symbol);

    28 			// UpdateModel(symbol);

    29 			uint newBound = (encoder.Range >> kNumBitModelTotalBits) * Prob;

    30 			if (symbol == 0)

    31 			{

    32 				encoder.Range = newBound;

    33 				Prob += (kBitModelTotal - Prob) >> kNumMoveBits;

    34 			}

    35 			else

    36 			{

    37 				encoder.Low += newBound;

    38 				encoder.Range -= newBound;

    39 				Prob -= (Prob) >> kNumMoveBits;

    40 			}

    41 			if (encoder.Range < Encoder.kTopValue)

    42 			{

    43 				encoder.Range <<= 8;

    44 				encoder.ShiftLow();

    45 			}

    46 		}

    47 

    48 		private static UInt32[] ProbPrices = new UInt32[kBitModelTotal >> kNumMoveReducingBits];

    49 

    50 		static BitEncoder()

    51 		{

    52 			const int kNumBits = (kNumBitModelTotalBits - kNumMoveReducingBits);

    53 			for (int i = kNumBits - 1; i >= 0; i--)

    54 			{

    55 				UInt32 start = (UInt32)1 << (kNumBits - i - 1);

    56 				UInt32 end = (UInt32)1 << (kNumBits - i);

    57 				for (UInt32 j = start; j < end; j++)

    58 					ProbPrices[j] = ((UInt32)i << kNumBitPriceShiftBits) +

    59 						(((end - j) << kNumBitPriceShiftBits) >> (kNumBits - i - 1));

    60 			}

    61 		}

    62 

    63 		public uint GetPrice(uint symbol)

    64 		{

    65 			return ProbPrices[(((Prob - symbol) ^ ((-(int)symbol))) & (kBitModelTotal - 1)) >> kNumMoveReducingBits];

    66 		}

    67 	  public uint GetPrice0() { return ProbPrices[Prob >> kNumMoveReducingBits]; }

    68 		public uint GetPrice1() { return ProbPrices[(kBitModelTotal - Prob) >> kNumMoveReducingBits]; }

    69 	}

    70 

    71 	struct BitDecoder

    72 	{

    73 		public const int kNumBitModelTotalBits = 11;

    74 		public const uint kBitModelTotal = (1 << kNumBitModelTotalBits);

    75 		const int kNumMoveBits = 5;

    76 

    77 		uint Prob;

    78 

    79 		public void UpdateModel(int numMoveBits, uint symbol)

    80 		{

    81 			if (symbol == 0)

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

    83 			else

    84 				Prob -= (Prob) >> numMoveBits;

    85 		}

    86 

    87 		public void Init() { Prob = kBitModelTotal >> 1; }

    88 

    89 		public uint Decode(RangeCoder.Decoder rangeDecoder)

    90 		{

    91 			uint newBound = (uint)(rangeDecoder.Range >> kNumBitModelTotalBits) * (uint)Prob;

    92 			if (rangeDecoder.Code < newBound)

    93 			{

    94 				rangeDecoder.Range = newBound;

    95 				Prob += (kBitModelTotal - Prob) >> kNumMoveBits;

    96 				if (rangeDecoder.Range < Decoder.kTopValue)

    97 				{

    98 					rangeDecoder.Code = (rangeDecoder.Code << 8) | (byte)rangeDecoder.Stream.ReadByte();

    99 					rangeDecoder.Range <<= 8;

   100 				}

   101 				return 0;

   102 			}

   103 			else

   104 			{

   105 				rangeDecoder.Range -= newBound;

   106 				rangeDecoder.Code -= newBound;

   107 				Prob -= (Prob) >> kNumMoveBits;

   108 				if (rangeDecoder.Range < Decoder.kTopValue)

   109 				{

   110 					rangeDecoder.Code = (rangeDecoder.Code << 8) | (byte)rangeDecoder.Stream.ReadByte();

   111 					rangeDecoder.Range <<= 8;

   112 				}

   113 				return 1;

   114 			}

   115 		}

   116 	}

   117 }