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 
InitSevenZip.Compression.RangeCoder.BitEncoder15 		public void Init() { Prob = kBitModelTotal >> 1; }
16 
UpdateModelSevenZip.Compression.RangeCoder.BitEncoder17 		public void UpdateModel(uint symbol)
18 		{
19 			if (symbol == 0)
20 				Prob += (kBitModelTotal - Prob) >> kNumMoveBits;
21 			else
22 				Prob -= (Prob) >> kNumMoveBits;
23 		}
24 
EncodeSevenZip.Compression.RangeCoder.BitEncoder25 		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 
BitEncoderSevenZip.Compression.RangeCoder.BitEncoder50 		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 
GetPriceSevenZip.Compression.RangeCoder.BitEncoder63 		public uint GetPrice(uint symbol)
64 		{
65 			return ProbPrices[(((Prob - symbol) ^ ((-(int)symbol))) & (kBitModelTotal - 1)) >> kNumMoveReducingBits];
66 		}
GetPrice0SevenZip.Compression.RangeCoder.BitEncoder67 	  public uint GetPrice0() { return ProbPrices[Prob >> kNumMoveReducingBits]; }
GetPrice1SevenZip.Compression.RangeCoder.BitEncoder68 		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 
UpdateModelSevenZip.Compression.RangeCoder.BitDecoder79 		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 
InitSevenZip.Compression.RangeCoder.BitDecoder87 		public void Init() { Prob = kBitModelTotal >> 1; }
88 
DecodeSevenZip.Compression.RangeCoder.BitDecoder89 		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 }
118