BitTreeDecoder.java

package sevenzip.compression.rangecoder;


public class BitTreeDecoder {

    short[] Models;

    int NumBitLevels;


    public BitTreeDecoder(int numBitLevels) {
        NumBitLevels = numBitLevels;
        Models = new short[1<<numBitLevels];
    }


    public void Init() {
        Decoder.InitBitModels(Models);
    }


    public int Decode(Decoder rangeDecoder) throws java.io.IOException {
        int m = 1;
        for (int bitIndex = NumBitLevels; bitIndex!=0; bitIndex--) {
            m = (m<<1)+rangeDecoder.DecodeBit(Models, m);
        }
        return m-(1<<NumBitLevels);
    }


    public int ReverseDecode(Decoder rangeDecoder) throws java.io.IOException {
        int m = 1;
        int symbol = 0;
        for (int bitIndex = 0; bitIndex<NumBitLevels; bitIndex++) {
            int bit = rangeDecoder.DecodeBit(Models, m);
            m <<= 1;
            m += bit;
            symbol |= (bit<<bitIndex);
        }
        return symbol;
    }


    public static int ReverseDecode(short[] Models, int startIndex,
            Decoder rangeDecoder, int NumBitLevels) throws java.io.IOException {
        int m = 1;
        int symbol = 0;
        for (int bitIndex = 0; bitIndex<NumBitLevels; bitIndex++) {
            int bit = rangeDecoder.DecodeBit(Models, startIndex+m);
            m <<= 1;
            m += bit;
            symbol |= (bit<<bitIndex);
        }
        return symbol;
    }

}