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package uk.ac.bristol.star.cdf.record;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.GZIPInputStream;
import uk.ac.bristol.star.cdf.CdfFormatException;
/**
* Defines a data compression type supported for compressing CDF data.
*
* @author Mark Taylor
* @since 19 Jun 2013
*/
public abstract class Compression {
/** No compression. */
public static final Compression NONE = new Compression( "NONE" ) {
public InputStream uncompressStream( InputStream in ) {
return in;
}
};
/** Run length encoding. */
public static final Compression RLE = new Compression( "RLE" ) {
public InputStream uncompressStream( InputStream in )
throws IOException {
return new RunLengthInputStream( in, (byte) 0 );
}
};
/** Huffman encoding. */
public static final Compression HUFF = new Compression( "HUFF" ) {
public InputStream uncompressStream( InputStream in )
throws IOException {
return new BitExpandInputStream.HuffmanInputStream( in );
}
};
/** Adaptive Huffman encoding. */
public static final Compression AHUFF = new Compression( "AHUFF" ) {
public InputStream uncompressStream( InputStream in )
throws IOException {
return new BitExpandInputStream.AdaptiveHuffmanInputStream( in );
}
};
/** Gzip compression. */
public static final Compression GZIP = new Compression( "GZIP" ) {
public InputStream uncompressStream( InputStream in )
throws IOException {
return new GZIPInputStream( in );
}
};
private final String name_;
/**
* Constructor.
*
* @param name compression format name
*/
protected Compression( String name ) {
name_ = name;
}
/**
* Turns a stream containing compressed data into a stream containing
* uncompressed data.
*
* @param in compressed input stream
* @return uncompressed input stream
*/
public abstract InputStream uncompressStream( InputStream in )
throws IOException;
/**
* Returns this compression format's name.
*
* @return name
*/
public String getName() {
return name_;
}
/**
* Returns a Compression object corresponding to a given compression code.
*
* @param cType compression code, as taken from the CPR cType field
* @return compression object
* @throws CdfFormatException if the compression type is unknown
*/
public static Compression getCompression( int cType )
throws CdfFormatException {
// The mapping is missing from the CDF Internal Format Description
// document, but cdf.h says:
// #define NO_COMPRESSION 0L
// #define RLE_COMPRESSION 1L
// #define HUFF_COMPRESSION 2L
// #define AHUFF_COMPRESSION 3L
// #define GZIP_COMPRESSION 5L
switch ( cType ) {
case 0: return NONE;
case 1: return RLE;
case 2: return HUFF;
case 3: return AHUFF;
case 5: return GZIP;
default:
throw new CdfFormatException( "Unknown compression format "
+ "cType=" + cType );
}
}
}
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