1 /* 2 * DeltaOptions 3 * 4 * Author: Lasse Collin <lasse.collin@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 */ DeltaOptions()45 public DeltaOptions() {} 46 47 /** 48 * Creates new Delta options and sets the distance to the given value. 49 */ DeltaOptions(int distance)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 */ setDistance(int distance)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 */ getDistance()70 public int getDistance() { 71 return distance; 72 } 73 getEncoderMemoryUsage()74 public int getEncoderMemoryUsage() { 75 return DeltaOutputStream.getMemoryUsage(); 76 } 77 getOutputStream(FinishableOutputStream out)78 public FinishableOutputStream getOutputStream(FinishableOutputStream out) { 79 return new DeltaOutputStream(out, this); 80 } 81 getDecoderMemoryUsage()82 public int getDecoderMemoryUsage() { 83 return 1; 84 } 85 getInputStream(InputStream in)86 public InputStream getInputStream(InputStream in) { 87 return new DeltaInputStream(in, distance); 88 } 89 getFilterEncoder()90 FilterEncoder getFilterEncoder() { 91 return new DeltaEncoder(this); 92 } 93 clone()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