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