1 package SevenZip.Compression.RangeCoder;

     2 

     3 public class BitTreeDecoder

     4 {

     5 	short[] Models;

     6 	int NumBitLevels;

     7 	

     8 	public BitTreeDecoder(int numBitLevels)

     9 	{

    10 		NumBitLevels = numBitLevels;

    11 		Models = new short[1 << numBitLevels];

    12 	}

    13 	

    14 	public void Init()

    15 	{

    16 		Decoder.InitBitModels(Models);

    17 	}

    18 	

    19 	public int Decode(Decoder rangeDecoder) throws java.io.IOException

    20 	{

    21 		int m = 1;

    22 		for (int bitIndex = NumBitLevels; bitIndex != 0; bitIndex--)

    23 			m = (m << 1) + rangeDecoder.DecodeBit(Models, m);

    24 		return m - (1 << NumBitLevels);

    25 	}

    26 	

    27 	public int ReverseDecode(Decoder rangeDecoder) throws java.io.IOException

    28 	{

    29 		int m = 1;

    30 		int symbol = 0;

    31 		for (int bitIndex = 0; bitIndex < NumBitLevels; bitIndex++)

    32 		{

    33 			int bit = rangeDecoder.DecodeBit(Models, m);

    34 			m <<= 1;

    35 			m += bit;

    36 			symbol |= (bit << bitIndex);

    37 		}

    38 		return symbol;

    39 	}

    40 	

    41 	public static int ReverseDecode(short[] Models, int startIndex,

    42 			Decoder rangeDecoder, int NumBitLevels) throws java.io.IOException

    43 	{

    44 		int m = 1;

    45 		int symbol = 0;

    46 		for (int bitIndex = 0; bitIndex < NumBitLevels; bitIndex++)

    47 		{

    48 			int bit = rangeDecoder.DecodeBit(Models, startIndex + m);

    49 			m <<= 1;

    50 			m += bit;

    51 			symbol |= (bit << bitIndex);

    52 		}

    53 		return symbol;

    54 	}

    55 }