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package com.sun.grizzly.lzma.compression.rangecoder;

/**
 * BitTreeDecoder
 *
 * @author Igor Pavlov
 */
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;
    }
}