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using System;
namespace SevenZip.Compression.RangeCoder
{
struct BitEncoder
{
public const int kNumBitModelTotalBits = 11;
public const uint kBitModelTotal = (1 << kNumBitModelTotalBits);
const int kNumMoveBits = 5;
const int kNumMoveReducingBits = 2;
public const int kNumBitPriceShiftBits = 6;
uint Prob;
public void Init() { Prob = kBitModelTotal >> 1; }
public void UpdateModel(uint symbol)
{
if (symbol == 0)
Prob += (kBitModelTotal - Prob) >> kNumMoveBits;
else
Prob -= (Prob) >> kNumMoveBits;
}
public void Encode(Encoder encoder, uint symbol)
{
// encoder.EncodeBit(Prob, kNumBitModelTotalBits, symbol);
// UpdateModel(symbol);
uint newBound = (encoder.Range >> kNumBitModelTotalBits) * Prob;
if (symbol == 0)
{
encoder.Range = newBound;
Prob += (kBitModelTotal - Prob) >> kNumMoveBits;
}
else
{
encoder.Low += newBound;
encoder.Range -= newBound;
Prob -= (Prob) >> kNumMoveBits;
}
if (encoder.Range < Encoder.kTopValue)
{
encoder.Range <<= 8;
encoder.ShiftLow();
}
}
private static UInt32[] ProbPrices = new UInt32[kBitModelTotal >> kNumMoveReducingBits];
static BitEncoder()
{
const int kNumBits = (kNumBitModelTotalBits - kNumMoveReducingBits);
for (int i = kNumBits - 1; i >= 0; i--)
{
UInt32 start = (UInt32)1 << (kNumBits - i - 1);
UInt32 end = (UInt32)1 << (kNumBits - i);
for (UInt32 j = start; j < end; j++)
ProbPrices[j] = ((UInt32)i << kNumBitPriceShiftBits) +
(((end - j) << kNumBitPriceShiftBits) >> (kNumBits - i - 1));
}
}
public uint GetPrice(uint symbol)
{
return ProbPrices[(((Prob - symbol) ^ ((-(int)symbol))) & (kBitModelTotal - 1)) >> kNumMoveReducingBits];
}
public uint GetPrice0() { return ProbPrices[Prob >> kNumMoveReducingBits]; }
public uint GetPrice1() { return ProbPrices[(kBitModelTotal - Prob) >> kNumMoveReducingBits]; }
}
struct BitDecoder
{
public const int kNumBitModelTotalBits = 11;
public const uint kBitModelTotal = (1 << kNumBitModelTotalBits);
const int kNumMoveBits = 5;
uint Prob;
public void UpdateModel(int numMoveBits, uint symbol)
{
if (symbol == 0)
Prob += (kBitModelTotal - Prob) >> numMoveBits;
else
Prob -= (Prob) >> numMoveBits;
}
public void Init() { Prob = kBitModelTotal >> 1; }
public uint Decode(RangeCoder.Decoder rangeDecoder)
{
uint newBound = (uint)(rangeDecoder.Range >> kNumBitModelTotalBits) * (uint)Prob;
if (rangeDecoder.Code < newBound)
{
rangeDecoder.Range = newBound;
Prob += (kBitModelTotal - Prob) >> kNumMoveBits;
if (rangeDecoder.Range < Decoder.kTopValue)
{
rangeDecoder.Code = (rangeDecoder.Code << 8) | (byte)rangeDecoder.Stream.ReadByte();
rangeDecoder.Range <<= 8;
}
return 0;
}
else
{
rangeDecoder.Range -= newBound;
rangeDecoder.Code -= newBound;
Prob -= (Prob) >> kNumMoveBits;
if (rangeDecoder.Range < Decoder.kTopValue)
{
rangeDecoder.Code = (rangeDecoder.Code << 8) | (byte)rangeDecoder.Stream.ReadByte();
rangeDecoder.Range <<= 8;
}
return 1;
}
}
}
}
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