source: josm/trunk/src/org/tukaani/xz/DeltaOptions.java@ 13928

/*
 * DeltaOptions
 *
 * Author: Lasse Collin <lasse.collin@tukaani.org>
 *
 * This file has been put into the public domain.
 * You can do whatever you want with this file.
 */

package org.tukaani.xz;

import java.io.InputStream;

/**
 * Delta filter options. The Delta filter can be used only as a non-last
 * filter in the chain, for example Delta + LZMA2.
 * <p>
 * Currently only simple byte-wise delta is supported. The only option
 * is the delta distance, which you should set to match your data.
 * It's not possible to provide a generic default value for it.
 * <p>
 * For example, with distance = 2 and eight-byte input
 * A1 B1 A2 B3 A3 B5 A4 B7, the output will be A1 B1 01 02 01 02 01 02.
 * <p>
 * The Delta filter can be good with uncompressed bitmap images. It can
 * also help with PCM audio, although special-purpose compressors like
 * FLAC will give much smaller result at much better compression speed.
 */
public class DeltaOptions extends FilterOptions {
    /**
     * Smallest supported delta calculation distance.
     */
    public static final int DISTANCE_MIN = 1;

    /**
     * Largest supported delta calculation distance.
     */
    public static final int DISTANCE_MAX = 256;

    private int distance = DISTANCE_MIN;

    /**
     * Creates new Delta options and sets the delta distance to 1 byte.
     */
    public DeltaOptions() {}

    /**
     * Creates new Delta options and sets the distance to the given value.
     */
    public DeltaOptions(int distance) throws UnsupportedOptionsException {
        setDistance(distance);
    }

    /**
     * Sets the delta distance in bytes. The new distance must be in
     * the range [DISTANCE_MIN, DISTANCE_MAX].
     */
    public void setDistance(int distance) throws UnsupportedOptionsException {
        if (distance < DISTANCE_MIN || distance > DISTANCE_MAX)
            throw new UnsupportedOptionsException(
                    "Delta distance must be in the range [" + DISTANCE_MIN
                    + ", " + DISTANCE_MAX + "]: " + distance);

        this.distance = distance;
    }

    /**
     * Gets the delta distance.
     */
    public int getDistance() {
        return distance;
    }

    public int getEncoderMemoryUsage() {
        return DeltaOutputStream.getMemoryUsage();
    }

    public FinishableOutputStream getOutputStream(FinishableOutputStream out,
                                                  ArrayCache arrayCache) {
        return new DeltaOutputStream(out, this);
    }

    public int getDecoderMemoryUsage() {
        return 1;
    }

    public InputStream getInputStream(InputStream in, ArrayCache arrayCache) {
        return new DeltaInputStream(in, distance);
    }

    FilterEncoder getFilterEncoder() {
        return new DeltaEncoder(this);
    }

    public Object clone() {
        try {
            return super.clone();
        } catch (CloneNotSupportedException e) {
            assert false;
            throw new RuntimeException();
        }
    }
}