Transcript
/*,
* LZW.java,
*,
* Created on 01 Dec 2005,
*,
* Implementation of LZW compression/decompression algorithm,
*/,
,
import java.io.* ;,
,
/**,
*,
* @author Moshe Fresko,
* @course Algorithmic Programming 1,
* @exercise 3,
*/,
,
public class LZW implements Compression,
{,
boolean stopped = false ;,
,
Dict dict ;,
// The bits that should be written for each code,
int numOfBits ;,
// The previous string that we should remember,
// in order to insert into the dictionary,
final ByteArray emptyBA = new ByteArray() ;,
ByteArray w=emptyBA ;,
// Constructor gets the number of bits to be written for each code,
public LZW(),
{,
numOfBits = 12 ;,
// Create a new Limited Dictionary,
// For maximum of 2^bits entries,
dict = new LimitedDict(1<=0) {,
if (stopped),
break ;,
code = encodeOneChar(next) ;,
if (code>=0),
writeCode(os,code) ;
},
code = encodeLast() ;,
if (code>=0),
writeCode(os,code) ;
os.flush() ;,
},
,
ByteArray decodeOne(int code) {,
" // Either ""ABA"" or null"," w=""AB
ByteArray str = dict.strFromNum(code) ;
if (str==null) {
str = w.conc(w.getAt(0)) ;
dict.add(str) ;
} else
if (! w.isEmpty())
dict.add(w.conc(str.getAt(0))) ;
w = str ;
return w ;
}
public void decompress(InputStream is, OutputStream os) throws IOException {
is = new BitInputStream(is) ;
ByteArray str ; // Next entry
int code ; // Next code to be read
while ((code=readCode(is))>=0) {
if (stopped)
break ;
str = decodeOne(code) ;
os.write(str.getBytes()) ;
}
}
public void stop()
{ stopped = true ; }
}
"
