/*
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 Aug 6, 2009
*/
package com.bigdata.util;
import it.unimi.dsi.bits.AbstractBitVector;
import java.nio.ByteBuffer;
import cern.colt.bitvector.BitVector;
/**
* Wraps a {@link ByteBuffer} as a read-only {@link BitVector}.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public class ByteBufferBitVector extends AbstractBitVector {
/**
* The {@link ByteBuffer} containing the backing data.
*/
final private ByteBuffer b;
/**
* The #of bits in the vector.
*/
private final long len;
/**
* The bit offset into the {@link ByteBuffer} of the first bit in the
* vector.
*/
private final long off;
final public long length() {
return len;
}
/**
* Ctor assumes that all bits in the buffer are used.
*
* @param b
* The buffer.
*/
public ByteBufferBitVector(final ByteBuffer b) {
this(b, 0/* offset */, b == null ? 0 : b.capacity() * 8/* len */);
}
/**
*
* @param b
* The buffer.
* @param off
* The offset from the start of the buffer for the view.
* @param len
* The #of bits which will be included in the view.
*/
public ByteBufferBitVector(final ByteBuffer b, final long off,
final long len) {
if (b == null)
throw new IllegalArgumentException();
if (len < 0)
throw new IllegalArgumentException();
if (len < 0)
throw new IllegalArgumentException();
if (off + len > b.capacity() * 8L)
throw new IllegalArgumentException();
this.b = b;
this.len = len;
this.off = off;
}
/**
* Return the index of the byte in which the bit with the given index is
* encoded.
*
* @param bitIndex
* The bit index.
*
* @return The byte index.
*/
final protected int byteIndexForBit(final long bitIndex) {
return ((int) ((bitIndex + off) / 8));
}
/**
* Return the offset within the byte in which the bit is coded of the bit
* (this is just the remainder <code>bitIndex % 8</code>).
*
* @param bitIndex
* The bit index into the byte[].
*
* @return The offset of the bit in the appropriate byte.
*/
final protected int withinByteIndexForBit(final long bitIndex) {
return (int) ((bitIndex + off) % 8);
}
/**
* Extract and return a bit coded flag.
*
* @param offset
* The offset in the buffer of the start of the byte[] sequence
* in which the bit coded flags are stored.
* @param index
* The index of the bit.
*
* @return The value of the bit.
*/
public boolean getBoolean(final long index) {
if (index < 0 || index >= len)
throw new IndexOutOfBoundsException();
return (b.get(byteIndexForBit(index)) & (1 << withinByteIndexForBit(index))) != 0;
}
// // @todo override for mutation.
// public boolean set(final long index, final boolean value) {
//
// throw new UnsupportedOperationException();
//
// }
}