src/org/tukaani/xz/rangecoder/RangeDecoderFromBuffer.java


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/*
 * RangeDecoderFromBuffer
 *
 * Authors: Lasse Collin <lasse.collin@tukaani.org>
 *          Igor Pavlov <http://7-zip.org/>
 *
 * This file has been put into the public domain.
 * You can do whatever you want with this file.
 */

package org.tukaani.xz.rangecoder;

import java.io.DataInputStream;
import java.io.IOException;
import org.tukaani.xz.CorruptedInputException;

public final class RangeDecoderFromBuffer extends RangeDecoder {
    private static final int INIT_SIZE = 5;

    private final byte[] buf;
    private int pos;

    public RangeDecoderFromBuffer(int inputSizeMax) {
        buf = new byte[inputSizeMax - INIT_SIZE];
        pos = buf.length;
    }

    public void prepareInputBuffer(DataInputStream in, int len)
            throws IOException {
        if (len < INIT_SIZE)
            throw new CorruptedInputException();

        if (in.readUnsignedByte() != 0x00)
            throw new CorruptedInputException();

        code = in.readInt();
        range = 0xFFFFFFFF;

        // Read the data to the end of the buffer. If the data is corrupt
        // and the decoder, reading from buf, tries to read past the end of
        // the data, ArrayIndexOutOfBoundsException will be thrown and
        // the problem is detected immediately.
        len -= INIT_SIZE;
        pos = buf.length - len;
        in.readFully(buf, pos, len);
    }

    public boolean isFinished() {
        return pos == buf.length && code == 0;
    }

    public void normalize() throws IOException {
        if ((range & TOP_MASK) == 0) {
            try {
                // If the input is corrupt, this might throw
                // ArrayIndexOutOfBoundsException.
                code = (code << SHIFT_BITS) | (buf[pos++] & 0xFF);
                range <<= SHIFT_BITS;
            } catch (ArrayIndexOutOfBoundsException e) {
                throw new CorruptedInputException();
            }
        }
    }
}