dmolony-DiskBrowser/src/com/bytezone/diskbrowser/utilities/LZW2.java

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package com.bytezone.diskbrowser.utilities;
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import java.util.Objects;
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// -----------------------------------------------------------------------------------//
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class LZW2 extends LZW
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// -----------------------------------------------------------------------------------//
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{
private int nextEntry = 0x100;
private String prev = "";
private int codeWord;
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// ---------------------------------------------------------------------------------//
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public LZW2 (byte[] buffer, int crc)
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// ---------------------------------------------------------------------------------//
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{
bytes = Objects.requireNonNull (buffer);
this.crc = crc;
crcBase = 0xFFFF;
codeWord = 0;
volume = buffer[0] & 0xFF;
runLengthChar = (byte) (buffer[1] & 0xFF);
int ptr = 2;
while (ptr < buffer.length - 1) // what is in the last byte?
{
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int rleLength = Utility.getWord (buffer, ptr);
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boolean lzwPerformed = (rleLength & 0x8000) != 0;
ptr += 2;
if (lzwPerformed)
{
rleLength &= 0x0FFF; // remove the LZW flag
if (rleLength == 0)
rleLength = TRACK_LENGTH;
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int chunkLength = Utility.getWord (buffer, ptr);
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ptr += 2;
setBuffer (buffer, ptr); // prepare to read n-bit integers
byte[] lzwBuffer = undoLZW (rleLength);
assert (chunkLength - 4) == bytesRead ();
if (rleLength == TRACK_LENGTH) // no run length encoding
chunks.add (lzwBuffer);
else
chunks.add (undoRLE (lzwBuffer, 0, lzwBuffer.length));
ptr += bytesRead (); // since the setBuffer()
}
else
{
nextEntry = 0x100;
if (rleLength == 0)
rleLength = TRACK_LENGTH;
if (rleLength == TRACK_LENGTH) // no run length encoding
{
byte[] originalBuffer = new byte[TRACK_LENGTH];
System.arraycopy (buffer, ptr, originalBuffer, 0, originalBuffer.length);
chunks.add (originalBuffer);
}
else
chunks.add (undoRLE (buffer, ptr, rleLength));
ptr += rleLength;
}
}
}
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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 buffer
int ptr = 0;
while (ptr < rleLength)
{
codeWord = readInt (width (nextEntry + 1));
if (codeWord == 0x100) // clear the table
{
nextEntry = 0x100;
codeWord = readInt (9);
prev = "";
}
String s = (nextEntry == codeWord) ? prev + prev.charAt (0) : st[codeWord];
if (nextEntry < st.length)
st[nextEntry++] = prev + s.charAt (0);
for (int i = 0; i < s.length (); i++)
lzwBuffer[ptr++] = (byte) s.charAt (i);
prev = s;
}
return lzwBuffer;
}
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// ---------------------------------------------------------------------------------//
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@Override
public String toString ()
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// ---------------------------------------------------------------------------------//
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{
StringBuilder text = new StringBuilder ();
text.append (String.format (" volume ............ %,d%n", volume));
text.append (String.format (" RLE char .......... $%02X", runLengthChar));
return text.toString ();
}
}