/*
* Copyright (c) 2005, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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*/
package com.sun.imageio.plugins.common;
import java.io.IOException;
import java.io.PrintStream;
import javax.imageio.stream.ImageOutputStream;
/*
* Modified from original LZWCompressor to change interface to passing a
* buffer of data to be compressed.
*/
public class LZWCompressor {
/** base underlying code size of data being compressed 8 for TIFF, 1 to 8 for GIF **/
int codeSize;
/** reserved clear code based on code size **/
int clearCode;
/** reserved end of data code based on code size **/
int endOfInfo;
/** current number bits output for each code **/
int numBits;
/** limit at which current number of bits code size has to be increased **/
int limit;
/** the prefix code which represents the predecessor string to current input point **/
short prefix;
/** output destination for bit codes **/
BitFile bf;
/** general purpose LZW string table **/
LZWStringTable lzss;
/** modify the limits of the code values in LZW encoding due to TIFF bug / feature **/
boolean tiffFudge;
/**
* @param out destination for compressed data
* @param codeSize the initial code size for the LZW compressor
* @param TIFF flag indicating that TIFF lzw fudge needs to be applied
* @exception IOException if underlying output stream error
**/
public LZWCompressor(ImageOutputStream out, int codeSize, boolean TIFF)
throws IOException
{
bf = new BitFile(out, !TIFF); // set flag for GIF as NOT tiff
this.codeSize = codeSize;
tiffFudge = TIFF;
clearCode = 1 << codeSize;
endOfInfo = clearCode + 1;
numBits = codeSize + 1;
limit = (1 << numBits) - 1;
if (tiffFudge) {
--limit;
}
prefix = (short)0xFFFF;
lzss = new LZWStringTable();
lzss.clearTable(codeSize);
bf.writeBits(clearCode, numBits);
}
/**
* @param buf data to be compressed to output stream
* @exception IOException if underlying output stream error
**/
public void compress(byte[] buf, int offset, int length)
throws IOException
{
int idx;
byte c;
short index;
int maxOffset = offset + length;
for (idx = offset; idx < maxOffset; ++idx) {
c = buf[idx];
if ((index = lzss.findCharString(prefix, c)) != -1) {
prefix = index;
} else {
bf.writeBits(prefix, numBits);
if (lzss.addCharString(prefix, c) > limit) {
if (numBits == 12) {
bf.writeBits(clearCode, numBits);
lzss.clearTable(codeSize);
numBits = codeSize + 1;
} else {
++numBits;
}
limit = (1 << numBits) - 1;
if (tiffFudge) {
--limit;
}
}
prefix = (short)((short)c & 0xFF);
}
}
}
/*
* Indicate to compressor that no more data to go so write out
* any remaining buffered data.
*
* @exception IOException if underlying output stream error
*/
public void flush() throws IOException {
if (prefix != -1) {
bf.writeBits(prefix, numBits);
}
bf.writeBits(endOfInfo, numBits);
bf.flush();
}
public void dump(PrintStream out) {
lzss.dump(out);
}
}