/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 2002-2006
* Sleepycat Software. All rights reserved.
*
* $Id: BitMap.java,v 1.1 2006/05/06 09:00:29 ckaestne Exp $
*/
package com.sleepycat.je.utilint;
import java.util.BitSet;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
/**
* Bitmap which supports indexing with long arguments. java.util.BitSet
* provides all the functionality and performance we need, but requires integer
* indexing.
*
* Long indexing is implemented by keeping a Map of java.util.BitSets, where
* each bitset covers 2^16 bits worth of values. The Bitmap may be sparse, in
* that each segment is only instantiated when needed.
*
* Note that this class is currently not thread safe; adding a new bitset
* segment is not protected.
*/
public class BitMap {
private static final int SEGMENT_SIZE = 16;
private static final int SEGMENT_MASK = 0xffff;
/*
* Map of segment value -> bitset, where the segment value is index >>16
*/
private Map bitSegments;
public BitMap() {
bitSegments = new HashMap();
}
/*
* @throws IndexOutOfBoundsException if index is negative.
*/
public void set(long index)
throws IndexOutOfBoundsException {
if (index < 0) {
throw new IndexOutOfBoundsException(index + " is negative.");
}
BitSet bitset = getBitSet(index, true);
if (bitset == null) {
throw new IllegalArgumentException(index + " is out of bounds");
}
int useIndex = getIntIndex(index);
bitset.set(useIndex);
}
/*
* @throws IndexOutOfBoundsException if index is negative.
*/
public boolean get(long index)
throws IndexOutOfBoundsException {
if (index < 0) {
throw new IndexOutOfBoundsException(index + " is negative.");
}
BitSet bitset = getBitSet(index, false);
if (bitset == null) {
return false;
}
int useIndex = getIntIndex(index);
return bitset.get(useIndex);
}
/*
* Since the BitMap is implemented by a collection of BitSets, return
* the one which covers the numeric range for this index.
*
* @param index the bit we want to access
* @param allowCreate if true, return the BitSet that would hold this
* index even if it wasn't previously set. If false, return null
* if the bit has not been set.
*/
private BitSet getBitSet(long index, boolean allowCreate) {
Long segmentId = new Long(index >> SEGMENT_SIZE);
BitSet bitset = (BitSet) bitSegments.get(segmentId);
if (allowCreate) {
if (bitset == null) {
bitset = new BitSet();
bitSegments.put(segmentId, bitset);
}
}
return bitset;
}
private int getIntIndex(long index) {
return (int) (index & SEGMENT_MASK);
}
/* For unit testing. */
int getNumSegments() {
return bitSegments.size();
}
/*
* Currently for unit testing, though note that java.util.BitSet does
* support cardinality().
*/
int cardinality() {
int count = 0;
Iterator iter = bitSegments.values().iterator();
while (iter.hasNext()) {
BitSet b = (BitSet) iter.next();
count += b.cardinality();
}
return count;
}
}