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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.lucene.util;
import java.io.IOException;
import org.apache.lucene.search.DocIdSetIterator;
/**
* Base implementation for a bit set.
*
* @lucene.internal
*/
public abstract class BitSet implements Bits, Accountable {
/**
* Build a {@link BitSet} from the content of the provided {@link DocIdSetIterator}. NOTE: this
* will fully consume the {@link DocIdSetIterator}.
*/
public static BitSet of(DocIdSetIterator it, int maxDoc) throws IOException {
final long cost = it.cost();
final int threshold = maxDoc >>> 7;
BitSet set;
if (cost < threshold) {
set = new SparseFixedBitSet(maxDoc);
} else {
set = new FixedBitSet(maxDoc);
}
set.or(it);
return set;
}
/**
* Clear all the bits of the set.
*
* Depending on the implementation, this may be significantly faster than clear(0, length).
*/
public void clear() {
// default implementation for compatibility
clear(0, length());
}
/** Set the bit at i. */
public abstract void set(int i);
/** Set the bit at i, returning true if it was previously set. */
public abstract boolean getAndSet(int i);
/** Clear the bit at i. */
public abstract void clear(int i);
/**
* Clears a range of bits.
*
* @param startIndex lower index
* @param endIndex one-past the last bit to clear
*/
public abstract void clear(int startIndex, int endIndex);
/** Return the number of bits that are set. NOTE: this method is likely to run in linear time */
public abstract int cardinality();
/**
* Return an approximation of the cardinality of this set. Some implementations may trade accuracy
* for speed if they have the ability to estimate the cardinality of the set without iterating
* over all the data. The default implementation returns {@link #cardinality()}.
*/
public abstract int approximateCardinality();
/**
* Returns the index of the last set bit before or on the index specified. -1 is returned if there
* are no more set bits.
*/
public abstract int prevSetBit(int index);
/**
* Returns the index of the first set bit starting at the index specified. {@link
* DocIdSetIterator#NO_MORE_DOCS} is returned if there are no more set bits.
*/
public int nextSetBit(int index) {
// Default implementation. Subclasses may be able to override with a more performant
// implementation.
return nextSetBit(index, length());
}
/**
* Returns the index of the first set bit from start (inclusive) until end (exclusive). {@link
* DocIdSetIterator#NO_MORE_DOCS} is returned if there are no more set bits.
*/
public abstract int nextSetBit(int start, int end);
/** Assert that the current doc is -1. */
protected final void checkUnpositioned(DocIdSetIterator iter) {
if (iter.docID() != -1) {
throw new IllegalStateException(
"This operation only works with an unpositioned iterator, got current position = "
+ iter.docID());
}
}
/**
* Does in-place OR of the bits provided by the iterator. The state of the iterator after this
* operation terminates is undefined.
*/
public void or(DocIdSetIterator iter) throws IOException {
checkUnpositioned(iter);
for (int doc = iter.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = iter.nextDoc()) {
set(doc);
}
}
}