/*
* 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.cassandra.utils;
import java.io.IOException;
import java.nio.ByteBuffer;
import org.apache.cassandra.utils.obs.IBitSet;
public abstract class BloomFilter implements IFilter
{
public final IBitSet bitset;
public final int hashCount;
BloomFilter(int hashes, IBitSet bitset)
{
this.hashCount = hashes;
this.bitset = bitset;
}
private long[] getHashBuckets(ByteBuffer key)
{
return getHashBuckets(key, hashCount, bitset.capacity());
}
protected abstract long[] hash(ByteBuffer b, int position, int remaining, long seed);
// Murmur is faster than an SHA-based approach and provides as-good collision
// resistance. The combinatorial generation approach described in
// http://www.eecs.harvard.edu/~kirsch/pubs/bbbf/esa06.pdf
// does prove to work in actual tests, and is obviously faster
// than performing further iterations of murmur.
long[] getHashBuckets(ByteBuffer b, int hashCount, long max)
{
long[] result = new long[hashCount];
long[] hash = this.hash(b, b.position(), b.remaining(), 0L);
for (int i = 0; i < hashCount; ++i)
{
result[i] = Math.abs((hash[0] + (long)i * hash[1]) % max);
}
return result;
}
public void add(ByteBuffer key)
{
for (long bucketIndex : getHashBuckets(key))
{
bitset.set(bucketIndex);
}
}
public boolean isPresent(ByteBuffer key)
{
for (long bucketIndex : getHashBuckets(key))
{
if (!bitset.get(bucketIndex))
{
return false;
}
}
return true;
}
public void clear()
{
bitset.clear();
}
public void close() throws IOException
{
bitset.close();
}
}