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- /* ====================================================================
- Licensed to the Apache Software Foundation (ASF) under one or more
- contributor license agreements. See the NOTICE file distributed with
- this work for additional information regarding copyright ownership.
- The ASF licenses this file to You under the Apache License, Version 2.0
- (the "License"); you may not use this file except in compliance with
- the License. You may obtain a copy of the License at
-
- http://www.apache.org/licenses/LICENSE-2.0
-
- Unless required by applicable law or agreed to in writing, software
- distributed under the License is distributed on an "AS IS" BASIS,
- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- See the License for the specific language governing permissions and
- limitations under the License.
- ==================================================================== */
- package org.apache.poi.hdgf;
-
- import java.io.ByteArrayOutputStream;
- import java.io.IOException;
- import java.io.InputStream;
- import java.io.OutputStream;
-
- import org.apache.poi.util.LZWDecompresser;
-
- /**
- * A decoder for the crazy LZW implementation used
- * in Visio.
- * According to VSDump, "it's a slightly perverted version of LZW
- * compression, with inverted meaning of flag byte and 0xFEE as an
- * 'initial shift'". It uses 12 bit codes
- * (http://www.gnome.ru/projects/vsdump_en.html)
- *
- * Two good resources on LZW are:
- * http://en.wikipedia.org/wiki/LZW
- * http://marknelson.us/1989/10/01/lzw-data-compression/
- */
- public class HDGFLZW extends LZWDecompresser {
- public HDGFLZW() {
- // Out flag is the wrong way round!
- // Length wise, we're 3 longer than we say, so the max len is 19
- // Endian wise, we're little endian, so 0x1234 is pos 0x312
- super(false, 3, false);
- }
-
- /**
- * Compress the given input stream, returning the array of bytes
- * of the compressed input
- *
- * @param src the compression source byte
- * @return the compressed stream as bytes
- *
- * @throws IOException when the InputStream can't be read
- */
- public byte[] compress(InputStream src) throws IOException {
- ByteArrayOutputStream res = new ByteArrayOutputStream();
- compress(src,res);
- return res.toByteArray();
- }
-
- /**
- * We have a slight shift by 18 bytes
- */
- @Override
- protected int adjustDictionaryOffset(int pntr) {
- if(pntr > 4078) {
- pntr = pntr - 4078;
- } else {
- pntr = pntr + 18;
- }
- return pntr;
- }
-
- /**
- * We want an empty dictionary, so do nothing
- */
- @Override
- protected int populateDictionary(byte[] dict) {
- return 0;
- }
-
- /**
- * Performs the Visio compatible streaming LZW compression.
- *
- * @param src the input bytes for the compression
- * @param res the OutputStream which receives the compressed bytes
- *
- * @throws IOException when the InputStream can't be read
- * or the OutputStream can't be written to
- */
- public void compress(InputStream src, OutputStream res) throws IOException {
- HDGFLZWCompressor c = new HDGFLZWCompressor(res);
- c.compress(src);
- }
- }
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