content: /*
   * 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 org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import org.apache.cassandra.io.util.DataOutputStreamPlus;
  import org.apache.cassandra.utils.concurrent.Ref;
  import org.apache.cassandra.utils.obs.IBitSet;
  import org.apache.cassandra.utils.obs.OffHeapBitSet;
  
  public class FilterFactory
  {
      public static final IFilter AlwaysPresent = AlwaysPresentFilter.instance;
  
      private static final Logger logger = LoggerFactory.getLogger(FilterFactory.class);
      private static final long BITSET_EXCESS = 20;
  
      /**
       * @return A BloomFilter with the lowest practical false positive
       *         probability for the given number of elements.
       */
      public static IFilter getFilter(long numElements, int targetBucketsPerElem)
      {
          int maxBucketsPerElement = Math.max(1, BloomCalculations.maxBucketsPerElement(numElements));
          int bucketsPerElement = Math.min(targetBucketsPerElem, maxBucketsPerElement);
          if (bucketsPerElement < targetBucketsPerElem)
          {
              logger.warn("Cannot provide an optimal BloomFilter for {} elements ({}/{} buckets per element).", numElements, bucketsPerElement, targetBucketsPerElem);
          }
          BloomCalculations.BloomSpecification spec = BloomCalculations.computeBloomSpec(bucketsPerElement);
          return createFilter(spec.K, numElements, spec.bucketsPerElement);
      }
  
      /**
       * @return The smallest BloomFilter that can provide the given false
       *         positive probability rate for the given number of elements.
       *
       *         Asserts that the given probability can be satisfied using this
       *         filter.
       */
      public static IFilter getFilter(long numElements, double maxFalsePosProbability)
      {
          assert maxFalsePosProbability <= 1.0 : "Invalid probability";
          if (maxFalsePosProbability == 1.0)
              return FilterFactory.AlwaysPresent;
          int bucketsPerElement = BloomCalculations.maxBucketsPerElement(numElements);
          BloomCalculations.BloomSpecification spec = BloomCalculations.computeBloomSpec(bucketsPerElement, maxFalsePosProbability);
          return createFilter(spec.K, numElements, spec.bucketsPerElement);
      }
  
      private static IFilter createFilter(int hash, long numElements, int bucketsPer)
      {
          long numBits = (numElements * bucketsPer) + BITSET_EXCESS;
          IBitSet bitset = new OffHeapBitSet(numBits);
          return new BloomFilter(hash, bitset);
      }
  
      private static class AlwaysPresentFilter implements IFilter
      {
          public static final AlwaysPresentFilter instance = new AlwaysPresentFilter();
  
          private AlwaysPresentFilter() { }
  
          public boolean isPresent(FilterKey key)
          {
              return true;
          }
  
          public void add(FilterKey key) { }
  
          public void clear() { }
  
          public void close() { }
  
          public IFilter sharedCopy()
          {
              return this;
          }
  
          public Throwable close(Throwable accumulate)
          {
              return accumulate;
          }
  
          public void addTo(Ref.IdentityCollection identities)
          {
          }
  
          public long serializedSize(boolean oldSerializationFormat) { return 0; }
  
          @Override
          public void serialize(DataOutputStreamPlus out, boolean oldSerializationFormat) throws IOException
          {
              // no-op
          }
  
          @Override
          public long offHeapSize()
          {
              return 0;
          }
  
          @Override
          public boolean isInformative()
          {
              return false;
          }
      }
  }
  