tsfile/src/main/java/org/apache/iotdb/tsfile/utils/BloomFilter.java

/*
 * 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.iotdb.tsfile.utils;

import org.apache.iotdb.tsfile.common.conf.TSFileConfig;

import java.util.BitSet;

public class BloomFilter {

  private static final int MINIMAL_SIZE = 256;
  private static final int MAXIMAL_HASH_FUNCTION_SIZE = 8;
  private static final int[] SEEDS = new int[] {5, 7, 11, 19, 31, 37, 43, 59};
  private int size;
  private int hashFunctionSize;
  private BitSet bits;
  private HashFunction[] func;

  // do not try to initialize the filter by construction method
  private BloomFilter(byte[] bytes, int size, int hashFunctionSize) {
    this.size = size;
    this.hashFunctionSize = hashFunctionSize;
    func = new HashFunction[hashFunctionSize];
    for (int i = 0; i < hashFunctionSize; i++) {
      func[i] = new HashFunction(size, SEEDS[i]);
    }

    bits = BitSet.valueOf(bytes);
  }

  private BloomFilter(int size, int hashFunctionSize) {
    this.size = size;
    this.hashFunctionSize = hashFunctionSize;
    func = new HashFunction[hashFunctionSize];
    for (int i = 0; i < hashFunctionSize; i++) {
      func[i] = new HashFunction(size, SEEDS[i]);
    }

    bits = new BitSet(size);
  }

  /**
   * get empty bloom filter
   *
   * @param errorPercent the tolerant percent of error of the bloom filter
   * @param numOfString the number of string want to store in the bloom filter
   * @return empty bloom
   */
  public static BloomFilter getEmptyBloomFilter(double errorPercent, int numOfString) {
    errorPercent = Math.max(errorPercent, TSFileConfig.MIN_BLOOM_FILTER_ERROR_RATE);
    errorPercent = Math.min(errorPercent, TSFileConfig.MAX_BLOOM_FILTER_ERROR_RATE);

    double ln2 = Math.log(2);
    int size = (int) (-numOfString * Math.log(errorPercent) / ln2 / ln2) + 1;
    int hashFunctionSize = (int) (-Math.log(errorPercent) / ln2) + 1;
    return new BloomFilter(
        Math.max(MINIMAL_SIZE, size), Math.min(MAXIMAL_HASH_FUNCTION_SIZE, hashFunctionSize));
  }

  /**
   * build bloom filter by bytes
   *
   * @param bytes bytes of bits
   * @return bloom filter
   */
  public static BloomFilter buildBloomFilter(byte[] bytes, int size, int hashFunctionSize) {
    return new BloomFilter(bytes, size, Math.min(MAXIMAL_HASH_FUNCTION_SIZE, hashFunctionSize));
  }

  public int getHashFunctionSize() {
    return hashFunctionSize;
  }

  public int getSize() {
    return size;
  }

  public void setSize(int size) {
    this.size = size;
  }

  public void add(String value) {
    for (HashFunction f : func) {
      bits.set(f.hash(value), true);
    }
  }

  public boolean contains(String value) {
    if (value == null) {
      return false;
    }
    boolean ret = true;
    int index = 0;
    while (ret && index < hashFunctionSize) {
      ret = bits.get(func[index++].hash(value));
    }

    return ret;
  }

  public int getBitCount() {
    int res = 0;
    for (int i = 0; i < size; i++) {
      res += bits.get(i) ? 1 : 0;
    }

    return res;
  }

  public byte[] serialize() {
    return bits.toByteArray();
  }

  private class HashFunction {

    private int cap;
    private int seed;

    HashFunction(int cap, int seed) {
      this.cap = cap;
      this.seed = seed;
    }

    public int hash(String value) {
      int res = Murmur128Hash.hash(value, seed);
      if (res == Integer.MIN_VALUE) {
        res = 0;
      }

      return Math.abs(res) % cap;
    }
  }
}