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      1 /*
      2  * DeltaOptions
      3  *
      4  * Author: Lasse Collin <lasse.collin (at) tukaani.org>
      5  *
      6  * This file has been put into the public domain.
      7  * You can do whatever you want with this file.
      8  */
      9 
     10 package org.tukaani.xz;
     11 
     12 import java.io.InputStream;
     13 
     14 /**
     15  * Delta filter options. The Delta filter can be used only as a non-last
     16  * filter in the chain, for example Delta + LZMA2.
     17  * <p>
     18  * Currently only simple byte-wise delta is supported. The only option
     19  * is the delta distance, which you should set to match your data.
     20  * It's not possible to provide a generic default value for it.
     21  * <p>
     22  * For example, with distance = 2 and eight-byte input
     23  * A1 B1 A2 B3 A3 B5 A4 B7, the output will be A1 B1 01 02 01 02 01 02.
     24  * <p>
     25  * The Delta filter can be good with uncompressed bitmap images. It can
     26  * also help with PCM audio, although special-purpose compressors like
     27  * FLAC will give much smaller result at much better compression speed.
     28  */
     29 public class DeltaOptions extends FilterOptions {
     30     /**
     31      * Smallest supported delta calculation distance.
     32      */
     33     public static final int DISTANCE_MIN = 1;
     34 
     35     /**
     36      * Largest supported delta calculation distance.
     37      */
     38     public static final int DISTANCE_MAX = 256;
     39 
     40     private int distance = DISTANCE_MIN;
     41 
     42     /**
     43      * Creates new Delta options and sets the delta distance to 1 byte.
     44      */
     45     public DeltaOptions() {}
     46 
     47     /**
     48      * Creates new Delta options and sets the distance to the given value.
     49      */
     50     public DeltaOptions(int distance) throws UnsupportedOptionsException {
     51         setDistance(distance);
     52     }
     53 
     54     /**
     55      * Sets the delta distance in bytes. The new distance must be in
     56      * the range [DISTANCE_MIN, DISTANCE_MAX].
     57      */
     58     public void setDistance(int distance) throws UnsupportedOptionsException {
     59         if (distance < DISTANCE_MIN || distance > DISTANCE_MAX)
     60             throw new UnsupportedOptionsException(
     61                     "Delta distance must be in the range [" + DISTANCE_MIN
     62                     + ", " + DISTANCE_MAX + "]: " + distance);
     63 
     64         this.distance = distance;
     65     }
     66 
     67     /**
     68      * Gets the delta distance.
     69      */
     70     public int getDistance() {
     71         return distance;
     72     }
     73 
     74     public int getEncoderMemoryUsage() {
     75         return DeltaOutputStream.getMemoryUsage();
     76     }
     77 
     78     public FinishableOutputStream getOutputStream(FinishableOutputStream out) {
     79         return new DeltaOutputStream(out, this);
     80     }
     81 
     82     public int getDecoderMemoryUsage() {
     83         return 1;
     84     }
     85 
     86     public InputStream getInputStream(InputStream in) {
     87         return new DeltaInputStream(in, distance);
     88     }
     89 
     90     FilterEncoder getFilterEncoder() {
     91         return new DeltaEncoder(this);
     92     }
     93 
     94     public Object clone() {
     95         try {
     96             return super.clone();
     97         } catch (CloneNotSupportedException e) {
     98             assert false;
     99             throw new RuntimeException();
    100         }
    101     }
    102 }
    103