88 lines
2.3 KiB
Java
88 lines
2.3 KiB
Java
package com.bytezone.diskbrowser;
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import java.util.Objects;
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import com.bytezone.common.Utility;
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class LZW1 extends LZW
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{
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public LZW1 (byte[] buffer)
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{
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bytes = Objects.requireNonNull (buffer);
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crc = Utility.getWord (buffer, 0);
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crcBase = 0;
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volume = buffer[2] & 0xFF;
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runLengthChar = (byte) (buffer[3] & 0xFF);
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int ptr = 4;
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while (ptr < buffer.length - 1) // what is in the last byte?
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{
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int rleLength = Utility.getWord (buffer, ptr);
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int lzwPerformed = buffer[ptr + 2] & 0xFF;
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ptr += 3;
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if (lzwPerformed != 0)
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{
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setBuffer (buffer, ptr); // prepare to read n-bit integers
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byte[] lzwBuffer = undoLZW (rleLength);
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if (rleLength == TRACK_LENGTH) // no run length encoding
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chunks.add (lzwBuffer);
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else
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chunks.add (undoRLE (lzwBuffer, 0, lzwBuffer.length));
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ptr += bytesRead (); // since the setBuffer()
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}
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else
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{
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if (rleLength == TRACK_LENGTH) // no run length encoding
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{
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byte[] originalBuffer = new byte[TRACK_LENGTH];
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System.arraycopy (buffer, ptr, originalBuffer, 0, originalBuffer.length);
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chunks.add (originalBuffer);
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}
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else
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chunks.add (undoRLE (buffer, ptr, rleLength));
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ptr += rleLength;
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}
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}
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}
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protected byte[] undoLZW (int rleLength)
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{
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byte[] lzwBuffer = new byte[rleLength]; // must fill this array from input
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int ptr = 0;
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int nextEntry = 0x100; // always start with a fresh table
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String prev = "";
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while (ptr < rleLength)
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{
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int codeWord = readInt (width (nextEntry + 1));
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String s = (nextEntry == codeWord) ? prev + prev.charAt (0) : st[codeWord];
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if (nextEntry < st.length)
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st[nextEntry++] = prev + s.charAt (0);
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for (int i = 0; i < s.length (); i++)
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lzwBuffer[ptr++] = (byte) s.charAt (i);
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prev = s;
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}
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return lzwBuffer;
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}
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@Override
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public String toString ()
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{
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StringBuilder text = new StringBuilder ();
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text.append (String.format (" crc ............... %,d (%04X)%n", crc, crc));
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text.append (String.format (" volume ............ %,d%n", volume));
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text.append (String.format (" RLE char .......... $%02X", runLengthChar));
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return text.toString ();
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}
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} |