com.sun.pdfview.decode.LZWDecode Maven / Gradle / Ivy
/*
* $Id: LZWDecode.java,v 1.4 2009/02/22 00:45:32 tomoke Exp $
*
* Copyright 2004 Sun Microsystems, Inc., 4150 Network Circle,
* Santa Clara, California 95054, U.S.A. All rights reserved.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
package com.sun.pdfview.decode;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import com.sun.pdfview.PDFObject;
import com.sun.pdfview.PDFParseException;
/**
* decode an LZW-encoded array of bytes. LZW is a patented algorithm.
*
* Feb 21, 2009 Legal statement on Intellectual Property from Unisys
* LZW Patent Information (http://www.unisys.com/about__unisys/lzw)
* License Information on GIF and Other LZW-based Technologies
*
* Unisys U.S. LZW Patent No. 4,558,302 expired on June 20, 2003,
* the counterpart patents in the United Kingdom, France, Germany and
* Italy expired on June 18, 2004, the Japanese counterpart patents
* expired on June 20, 2004 and the counterpart Canadian patent
* expired on July 7, 2004.
*
* Unisys Corporation holds and has patents pending on a number of
* improvements on the inventions claimed in the above-expired patents.
* Information on these improvement patents and terms under which they
* may be licensed can be obtained by contacting the following:
*
* Unisys Corporation
* Welch Patent Licensing Department
* Mail Stop E8-114
* Unisys Way
* Blue Bell, PA 19424
*
* Via the Internet, send email to [email protected].
*
* Via facsimile, send inquiries to Welch Patent Licensing Department at
* 215-986-3090.
*
* The above is presented for information purposes only, and is subject
* to change by Unisys. Additionally, this information should not be
* considered as legally obligating Unisys in any way with regard to license
* availability, or as to the terms and conditions offered for a license,
* or with regard to the interpretation of any license agreements.
* You should consult with your own legal counsel regarding your
* particular situation.
*
*
* @author Mike Wessler
*/
public class LZWDecode {
ByteBuffer buf;
int bytepos;
int bitpos;
byte[] dict[] = new byte[4096][];
int dictlen = 0;
int bitspercode = 9;
static int STOP = 257;
static int CLEARDICT = 256;
/**
* initialize this decoder with an array of encoded bytes
* @param buf the buffer of bytes
*/
private LZWDecode(ByteBuffer buf) throws PDFParseException {
for (int i = 0; i < 256; i++) {
dict[i] = new byte[1];
dict[i][0] = (byte) i;
}
dictlen = 258;
bitspercode = 9;
this.buf = buf;
bytepos = 0;
bitpos = 0;
}
/**
* reset the dictionary to the initial 258 entries
*/
private void resetDict() {
dictlen = 258;
bitspercode = 9;
}
/**
* get the next code from the input stream
*/
private int nextCode() {
int fillbits = bitspercode;
int value = 0;
if (bytepos >= buf.limit() - 1) {
return -1;
}
while (fillbits > 0) {
int nextbits = buf.get(bytepos); // bitsource
int bitsfromhere = 8 - bitpos; // how many bits can we take?
if (bitsfromhere > fillbits) { // don't take more than we need
bitsfromhere = fillbits;
}
value |= ((nextbits >> (8 - bitpos - bitsfromhere)) &
(0xff >> (8 - bitsfromhere))) << (fillbits - bitsfromhere);
fillbits -= bitsfromhere;
bitpos += bitsfromhere;
if (bitpos >= 8) {
bitpos = 0;
bytepos++;
}
}
return value;
}
/**
* decode the array.
* @return the uncompressed byte array
*/
private ByteBuffer decode() throws PDFParseException {
// algorithm derived from:
// http://www.rasip.fer.hr/research/compress/algorithms/fund/lz/lzw.html
// and the PDFReference
int cW = CLEARDICT;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
while (true) {
int pW = cW;
cW = nextCode();
if (cW == -1) {
throw new PDFParseException("Missed the stop code in LZWDecode!");
}
if (cW == STOP) {
break;
} else if (cW == CLEARDICT) {
resetDict();
// pW= -1;
} else if (pW == CLEARDICT) {
baos.write(dict[cW], 0, dict[cW].length);
} else {
if (cW < dictlen) { // it's a code in the dictionary
baos.write(dict[cW], 0, dict[cW].length);
byte[] p = new byte[dict[pW].length + 1];
System.arraycopy(dict[pW], 0, p, 0, dict[pW].length);
p[dict[pW].length] = dict[cW][0];
dict[dictlen++] = p;
} else { // not in the dictionary (should==dictlen)
// if (cW!=dictlen) {
// System.out.println("Got a bouncy code: "+cW+" (dictlen="+dictlen+")");
// }
byte[] p = new byte[dict[pW].length + 1];
System.arraycopy(dict[pW], 0, p, 0, dict[pW].length);
p[dict[pW].length] = p[0];
baos.write(p, 0, p.length);
dict[dictlen++] = p;
}
if (dictlen >= (1 << bitspercode) - 1 && bitspercode < 12) {
bitspercode++;
}
}
}
return ByteBuffer.wrap(baos.toByteArray());
}
/**
* decode an array of LZW-encoded bytes to a byte array.
*
* @param buf the buffer of encoded bytes
* @param params parameters for the decoder (unused)
* @return the decoded uncompressed bytes
*/
public static ByteBuffer decode(ByteBuffer buf, PDFObject params)
throws IOException {
// decode the array
LZWDecode me = new LZWDecode(buf);
ByteBuffer outBytes = me.decode();
// undo a predictor algorithm, if any was used
if (params != null && params.getDictionary().containsKey("Predictor")) {
Predictor predictor = Predictor.getPredictor(params);
if (predictor != null) {
outBytes = predictor.unpredict(outBytes);
}
}
return outBytes;
}
}