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com.webcodepro.shrinkit.io.NufxLzw1InputStream Maven / Gradle / Ivy

package com.webcodepro.shrinkit.io;

import java.io.IOException;
import java.io.InputStream;

import com.webcodepro.shrinkit.CRC16;

/**
 * The NufxLzw1InputStream reads a data fork or
 * resource fork written in the NuFX LZW/1 format.
 * 

* The layout of the LZW/1 data is as follows: *

* * * * * * * * * * * * * * * * * * * * * * * * * *
"Fork" Header
+0WordCRC-16 of the uncompressed data within the thread
+2ByteLow-level volume number use to format 5.25" disks
+3ByteRLE character used to decode this thread
Each subsequent 4K chunk of data
+0WordLength after RLE compression (if RLE is not used, length * will be 4096
+2ByteA $01 indicates LZW applied to this chunk; $00 that LZW * was not applied to this chunk
*

* Note that the LZW string table is cleared after * every chunk. * * @author [email protected] */ public class NufxLzw1InputStream extends InputStream { /** This is the raw data stream with all markers and compressed data. */ private LittleEndianByteInputStream dataStream; /** Used for an LZW-only InputStream. */ private LzwInputStream lzwStream; /** Used for an RLE-only InputStream. */ private RleInputStream rleStream; /** Used for an LZW+RLE InputStream. */ private InputStream lzwRleStream; /** This is the generic decompression stream from which we read. */ private InputStream decompressionStream; /** Counts the number of bytes in the 4096 byte chunk. */ private int bytesLeftInChunk; /** This is the CRC-16 for the uncompressed fork. */ private int givenCrc = -1; /** This is the volume number for 5.25" disks. */ private int volumeNumber; /** This is the RLE character to use. */ private int rleCharacter; /** Used to track the CRC of data we've extracted */ private CRC16 dataCrc = new CRC16(); /** * Create the LZW/1 input stream. */ public NufxLzw1InputStream(LittleEndianByteInputStream dataStream) { this.dataStream = dataStream; } /** * Read the next byte in the decompressed data stream. */ public int read() throws IOException { if (givenCrc == -1) { // read the data or resource fork header givenCrc = dataStream.readWord(); volumeNumber = dataStream.readByte(); rleCharacter = dataStream.readByte(); lzwStream = new LzwInputStream(new BitInputStream(dataStream, 9)); rleStream = new RleInputStream(dataStream, rleCharacter); lzwRleStream = new RleInputStream(lzwStream); } if (bytesLeftInChunk == 0) { // read the chunk header bytesLeftInChunk = 4096; // NuFX always reads 4096 bytes lzwStream.clearDictionary(); // Always clear dictionary int length = dataStream.readWord(); int lzwFlag = dataStream.readByte(); int flag = lzwFlag + (length == 4096 ? 0 : 2); switch (flag) { case 0: decompressionStream = dataStream; break; case 1: decompressionStream = lzwStream; break; case 2: decompressionStream = rleStream; break; case 3: decompressionStream = lzwRleStream; break; default: throw new IOException("Unknown type of decompression, flag = " + flag); } } // Now we can read a data byte int b = decompressionStream.read(); bytesLeftInChunk--; dataCrc.update(b); return b; } /** * Indicates if the computed CRC matches the CRC given in the data stream. */ public boolean isCrcValid() { return givenCrc == dataCrc.getValue(); } // GENERATED CODE public int getGivenCrc() { return givenCrc; } public void setGivenCrc(int givenCrc) { this.givenCrc = givenCrc; } public int getVolumeNumber() { return volumeNumber; } public void setVolumeNumber(int volumeNumber) { this.volumeNumber = volumeNumber; } public int getRleCharacter() { return rleCharacter; } public void setRleCharacter(int rleCharacter) { this.rleCharacter = rleCharacter; } public long getDataCrc() { return dataCrc.getValue(); } }