Decoder.java

package lzma.sdk.rangecoder;

import java.io.IOException;

public class Decoder
{
    private static final int kTopMask = ~((1 << 24) - 1);

    private static final int kNumBitModelTotalBits = 11;
    private static final int kBitModelTotal = (1 << kNumBitModelTotalBits);
    private static final int kNumMoveBits = 5;

    private int Range;
    private int Code;

    private java.io.InputStream Stream;

    public final void setStream(java.io.InputStream stream)
    {
        Stream = stream;
    }

    public final void releaseStream()
    {
        Stream = null;
    }

    public final void init() throws IOException
    {
        Code = 0;
        Range = -1;
        for (int i = 0; i < 5; i++)
        {
            Code = (Code << 8) | Stream.read();
        }
    }

    public final int decodeDirectBits(int numTotalBits) throws IOException
    {
        int result = 0;
        for (int i = numTotalBits; i != 0; i--)
        {
            Range >>>= 1;
            int t = ((Code - Range) >>> 31);
            Code -= Range & (t - 1);
            result = (result << 1) | (1 - t);

            if ((Range & kTopMask) == 0)
            {
                Code = (Code << 8) | Stream.read();
                Range <<= 8;
            }
        }
        return result;
    }

    public int decodeBit(short[] probs, int index) throws IOException
    {
        int prob = probs[index];
        int newBound = (Range >>> kNumBitModelTotalBits) * prob;
        if ((Code ^ 0x80000000) < (newBound ^ 0x80000000))
        {
            Range = newBound;
            probs[index] = (short) (prob + ((kBitModelTotal - prob) >>> kNumMoveBits));
            if ((Range & kTopMask) == 0)
            {
                Code = (Code << 8) | Stream.read();
                Range <<= 8;
            }
            return 0;
        }
        else
        {
            Range -= newBound;
            Code -= newBound;
            probs[index] = (short) (prob - ((prob) >>> kNumMoveBits));
            if ((Range & kTopMask) == 0)
            {
                Code = (Code << 8) | Stream.read();
                Range <<= 8;
            }
            return 1;
        }
    }

    public static void initBitModels(short[] probs)
    {
        for (int i = 0; i < probs.length; i++)
        {
            probs[i] = (kBitModelTotal >>> 1);
        }
    }
}