/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Oct 24, 2005
*/
package com.bigdata.io;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
/**
* Packing utility for non-negative <code>short</code> values.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public class ShortPacker
{
public ShortPacker() {
super();
}
/**
* Packs a non-negative short value into one or two bytes and writes them on
* <i>os </i>. A short in [0:127] is packed into one byte. Larger values are
* packed into two bytes. The high bit of the first byte is set if the value
* was packed into two bytes. If the bit is set, clear the high bit, read
* the next byte, and interpret the two bytes as a short value. Otherwise
* interpret the byte as a short value.
*
* @return The #of bytes into which the value was packed.
*/
static public int packShort(final DataOutput os, final short v)
throws IOException {
/*
* You can only pack non-negative values with this method.
*/
if( v < 0 ) {
throw new IllegalArgumentException( "negative value: v="+v );
}
if( v > 127 ) {
// the value requires two bytes.
os.write( (byte)((0xff & (v >> 8))|0x80) ); // note: set the high bit.
os.write( (byte)(0xff & v) );
return 2;
} else {
// the value fits in one byte.
os.write( (byte)(0xff & v) );
return 1;
}
}
/**
* Unpack a non-negative short value from the input stream.
*
* @param is The input stream.
*
* @return The short value.
*
* @throws IOException
*/
static public short unpackShort( final DataInput is ) throws IOException
{
short b = (short) is.readByte();
short v;
if( ( b & 0x80 ) != 0 ) {
// high bit is set.
v = (short) (( b & 0x7f ) << 8); // clear the high bit and shift over one byte.
b = is.readByte(); // read the next byte.
v |= ( b & 0xff ); // and combine it together with the high byte.
} else {
// high bit is clear.
v = b; // interpret the byte as a short value.
}
return (short) v;
}
/**
* Unpack a non-negative short value from the input stream.
*
* @param is The input stream.
*
* @return The short value.
*
* @throws IOException
*/
static public short unpackShort( final InputStream is ) throws IOException
{
short b = (short) readByte(is);
short v;
if( ( b & 0x80 ) != 0 ) {
// high bit is set.
v = (short) (( b & 0x7f ) << 8); // clear the high bit and shift over one byte.
b = readByte(is); // read the next byte.
v |= ( b & 0xff ); // and combine it together with the high byte.
} else {
// high bit is clear.
v = b; // interpret the byte as a short value.
}
return (short) v;
}
/**
* Read a byte from an {@link InputStream} ala {@link DataInput#readByte()}
*
* @param is
* The input stream.
* @return The byte.
* @throws IOException
* @throws EOFException
* if the end of the file has been reached.
*/
private static byte readByte(final InputStream is) throws IOException {
final int v = is.read();
if (v == -1)
throw new EOFException();
return (byte) (v & 0xff);
}
/**
* Returns the #of bytes into which a short value was packed based on the
* first byte.
*
* @param firstByte The first byte.
*
* @return The #of bytes (either one (1) or two (2)).
*/
static public int getNBytes( byte firstByte ) {
if( ( firstByte & 0x80 ) != 0 ) {
return 2;
} else {
return 1;
}
}
}