private int DecodeNextSymbol()
{
range = (ulong)(high - low) + 1;
var cummulativeSum = (uint)(((code - low + 1) * (ulong)totalSum - 1) / range);
var symbolIndex = GetSymbolIndexByCummulativeSum(cummulativeSum, sums);
high = GetHighForSymbol(symbolIndex);
low = GetLowForSymbol(symbolIndex);
while (true)
{
if (Intervals.ValuesAreInTheSameHalf(low, high))
{
high = BitwiseOperations.ShiftLeft1PositionAndFill(high, 1);
low = BitwiseOperations.ShiftLeft1PositionAndFill(low, 0);
}
else if (Intervals.IsInTheSecondQuarter(low) && Intervals.IsInTheThirdQuarter(high))
{
high = BitwiseOperations.ExtractSecondMostSignificantBitAndFill(high, 1);
low = BitwiseOperations.ExtractSecondMostSignificantBitAndFill(low, 0);
code ^= 0x40000000;
}
else
{
break;
}
code = BitwiseOperations.ShiftLeft1PositionAndFill(code, (byte)ReadNextBit());
}
return(symbolIndex);
}
public void EncodeSymbol(int symbolIndex)
{
range = (ulong)(high - low) + 1;
high = GetHighForSymbol(symbolIndex);
low = GetLowForSymbol(symbolIndex);
while (true)
{
if (Intervals.ValuesAreInTheSameHalf(low, high))
{
var bit = low >> 31;
bitWriter.WriteNBits(1, bit);
WriteUnderflowBits(~bit);
high = BitwiseOperations.ShiftLeft1PositionAndFill(high, 1);
low = BitwiseOperations.ShiftLeft1PositionAndFill(low, 0);
}
else if (Intervals.IsInTheSecondQuarter(low) && Intervals.IsInTheThirdQuarter(high))
{
high = BitwiseOperations.ExtractSecondMostSignificantBitAndFill(high, 1);
low = BitwiseOperations.ExtractSecondMostSignificantBitAndFill(low, 0);
underflowBits++;
}
else
{
return;
}
}
}
public void FinishEncoding()
{
uint valueToWrite;
if (Intervals.IsInTheFirstQuarter(low) && Intervals.IsInTheThirdQuarter(high))
{
valueToWrite = 1;
}
else if (Intervals.IsInTheSecondQuarter(low) && Intervals.IsInTheForthQuarter(high))
{
valueToWrite = 2;
}
else
{
valueToWrite = 1;
}
bitWriter.WriteNBits(1, valueToWrite >> 1);
WriteUnderflowBits(~(valueToWrite >> 1));
bitWriter.WriteNBits(1, valueToWrite & 1);
}