org.apache.poi.hdgf
Class HDGFLZW

java.lang.Object
  org.apache.poi.util.LZWDecompresser
      org.apache.poi.hdgf.HDGFLZW

public class HDGFLZW
extends 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/

Constructor Summary

HDGFLZW()

Method Summary

protected int	adjustDictionaryOffset(int pntr) We have a slight shift by 18 bytes
byte[]	compress(java.io.InputStream src) Compress the given input stream, returning the array of bytes of the compressed input
void	compress(java.io.InputStream src, java.io.OutputStream res) Performs the Visio compatible streaming LZW compression.
protected int	populateDictionary(byte[] dict) We want an empty dictionary, so do nothing

Methods inherited from class org.apache.poi.util.LZWDecompresser

decompress, decompress, fromByte, fromInt

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

HDGFLZW

public HDGFLZW()

Method Detail

compress

public byte[] compress(java.io.InputStream src)
                throws java.io.IOException

Compress the given input stream, returning the array of bytes of the compressed input

Throws:

java.io.IOException

adjustDictionaryOffset

protected int adjustDictionaryOffset(int pntr)

We have a slight shift by 18 bytes

Specified by:

adjustDictionaryOffset in class LZWDecompresser

populateDictionary

protected int populateDictionary(byte[] dict)

We want an empty dictionary, so do nothing

Specified by:

populateDictionary in class LZWDecompresser

compress

public void compress(java.io.InputStream src,
                     java.io.OutputStream res)
              throws java.io.IOException

Performs the Visio compatible streaming LZW compression.

Throws:

java.io.IOException