/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed 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 com.google.common.hash;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.common.math.LongMath;
import com.google.common.primitives.Ints;
import com.google.common.primitives.Longs;
import java.math.RoundingMode;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicLongArray;
import org.checkerframework.checker.nullness.qual.Nullable;

Collections of strategies of generating the k * log(M) bits required for an element to be mapped
to a BloomFilter of M bits and k hash functions. These strategies are part of the serialized form
of the Bloom filters that use them, thus they must be preserved as is (no updates allowed, only
introduction of new versions).
Important: the order of the constants cannot change, and they cannot be deleted - we depend on
their ordinal for BloomFilter serialization.
Author:
Dimitris Andreou, Kurt Alfred Kluever/**
 * Collections of strategies of generating the k * log(M) bits required for an element to be mapped
 * to a BloomFilter of M bits and k hash functions. These strategies are part of the serialized form
 * of the Bloom filters that use them, thus they must be preserved as is (no updates allowed, only
 * introduction of new versions).
 *
 * <p>Important: the order of the constants cannot change, and they cannot be deleted - we depend on
 * their ordinal for BloomFilter serialization.
 *
 * @author Dimitris Andreou
 * @author Kurt Alfred Kluever
 */
enum BloomFilterStrategies implements BloomFilter.Strategy {
  
See "Less Hashing, Same Performance: Building a Better Bloom Filter" by Adam Kirsch and Michael
Mitzenmacher. The paper argues that this trick doesn't significantly deteriorate the
performance of a Bloom filter (yet only needs two 32bit hash functions).
/**
   * See "Less Hashing, Same Performance: Building a Better Bloom Filter" by Adam Kirsch and Michael
   * Mitzenmacher. The paper argues that this trick doesn't significantly deteriorate the
   * performance of a Bloom filter (yet only needs two 32bit hash functions).
   */
  MURMUR128_MITZ_32() {
    @Override
    public <T> boolean put(
        T object, Funnel<? super T> funnel, int numHashFunctions, LockFreeBitArray bits) {
      long bitSize = bits.bitSize();
      long hash64 = Hashing.murmur3_128().hashObject(object, funnel).asLong();
      int hash1 = (int) hash64;
      int hash2 = (int) (hash64 >>> 32);

      boolean bitsChanged = false;
      for (int i = 1; i <= numHashFunctions; i++) {
        int combinedHash = hash1 + (i * hash2);
        // Flip all the bits if it's negative (guaranteed positive number)
        if (combinedHash < 0) {
          combinedHash = ~combinedHash;
        }
        bitsChanged |= bits.set(combinedHash % bitSize);
      }
      return bitsChanged;
    }

    @Override
    public <T> boolean mightContain(
        T object, Funnel<? super T> funnel, int numHashFunctions, LockFreeBitArray bits) {
      long bitSize = bits.bitSize();
      long hash64 = Hashing.murmur3_128().hashObject(object, funnel).asLong();
      int hash1 = (int) hash64;
      int hash2 = (int) (hash64 >>> 32);

      for (int i = 1; i <= numHashFunctions; i++) {
        int combinedHash = hash1 + (i * hash2);
        // Flip all the bits if it's negative (guaranteed positive number)
        if (combinedHash < 0) {
          combinedHash = ~combinedHash;
        }
        if (!bits.get(combinedHash % bitSize)) {
          return false;
        }
      }
      return true;
    }
  },
  
This strategy uses all 128 bits of Hashing.murmur3_128 when hashing. It looks different than the implementation in MURMUR128_MITZ_32 because we're avoiding the multiplication in the loop and doing a (much simpler) += hash2. We're also changing the index to a positive number by AND'ing with Long.MAX_VALUE instead of flipping the bits. /**
   * This strategy uses all 128 bits of {@link Hashing#murmur3_128} when hashing. It looks different
   * than the implementation in MURMUR128_MITZ_32 because we're avoiding the multiplication in the
   * loop and doing a (much simpler) += hash2. We're also changing the index to a positive number by
   * AND'ing with Long.MAX_VALUE instead of flipping the bits.
   */
  MURMUR128_MITZ_64() {
    @Override
    public <T> boolean put(
        T object, Funnel<? super T> funnel, int numHashFunctions, LockFreeBitArray bits) {
      long bitSize = bits.bitSize();
      byte[] bytes = Hashing.murmur3_128().hashObject(object, funnel).getBytesInternal();
      long hash1 = lowerEight(bytes);
      long hash2 = upperEight(bytes);

      boolean bitsChanged = false;
      long combinedHash = hash1;
      for (int i = 0; i < numHashFunctions; i++) {
        // Make the combined hash positive and indexable
        bitsChanged |= bits.set((combinedHash & Long.MAX_VALUE) % bitSize);
        combinedHash += hash2;
      }
      return bitsChanged;
    }

    @Override
    public <T> boolean mightContain(
        T object, Funnel<? super T> funnel, int numHashFunctions, LockFreeBitArray bits) {
      long bitSize = bits.bitSize();
      byte[] bytes = Hashing.murmur3_128().hashObject(object, funnel).getBytesInternal();
      long hash1 = lowerEight(bytes);
      long hash2 = upperEight(bytes);

      long combinedHash = hash1;
      for (int i = 0; i < numHashFunctions; i++) {
        // Make the combined hash positive and indexable
        if (!bits.get((combinedHash & Long.MAX_VALUE) % bitSize)) {
          return false;
        }
        combinedHash += hash2;
      }
      return true;
    }

    private /* static */ long lowerEight(byte[] bytes) {
      return Longs.fromBytes(
          bytes[7], bytes[6], bytes[5], bytes[4], bytes[3], bytes[2], bytes[1], bytes[0]);
    }

    private /* static */ long upperEight(byte[] bytes) {
      return Longs.fromBytes(
          bytes[15], bytes[14], bytes[13], bytes[12], bytes[11], bytes[10], bytes[9], bytes[8]);
    }
  };

  
Models a lock-free array of bits.
We use this instead of java.util.BitSet because we need access to the array of longs and we
need compare-and-swap.
/**
   * Models a lock-free array of bits.
   *
   * <p>We use this instead of java.util.BitSet because we need access to the array of longs and we
   * need compare-and-swap.
   */
  static final class LockFreeBitArray {
    private static final int LONG_ADDRESSABLE_BITS = 6;
    final AtomicLongArray data;
    private final LongAddable bitCount;

    LockFreeBitArray(long bits) {
      this(new long[Ints.checkedCast(LongMath.divide(bits, 64, RoundingMode.CEILING))]);
    }

    // Used by serialization
    LockFreeBitArray(long[] data) {
      checkArgument(data.length > 0, "data length is zero!");
      this.data = new AtomicLongArray(data);
      this.bitCount = LongAddables.create();
      long bitCount = 0;
      for (long value : data) {
        bitCount += Long.bitCount(value);
      }
      this.bitCount.add(bitCount);
    }

    
Returns true if the bit changed value. /** Returns true if the bit changed value. */
    boolean set(long bitIndex) {
      if (get(bitIndex)) {
        return false;
      }

      int longIndex = (int) (bitIndex >>> LONG_ADDRESSABLE_BITS);
      long mask = 1L << bitIndex; // only cares about low 6 bits of bitIndex

      long oldValue;
      long newValue;
      do {
        oldValue = data.get(longIndex);
        newValue = oldValue | mask;
        if (oldValue == newValue) {
          return false;
        }
      } while (!data.compareAndSet(longIndex, oldValue, newValue));

      // We turned the bit on, so increment bitCount.
      bitCount.increment();
      return true;
    }

    boolean get(long bitIndex) {
      return (data.get((int) (bitIndex >>> 6)) & (1L << bitIndex)) != 0;
    }

    
Careful here: if threads are mutating the atomicLongArray while this method is executing, the
final long[] will be a "rolling snapshot" of the state of the bit array. This is usually good
enough, but should be kept in mind.
/**
     * Careful here: if threads are mutating the atomicLongArray while this method is executing, the
     * final long[] will be a "rolling snapshot" of the state of the bit array. This is usually good
     * enough, but should be kept in mind.
     */
    public static long[] toPlainArray(AtomicLongArray atomicLongArray) {
      long[] array = new long[atomicLongArray.length()];
      for (int i = 0; i < array.length; ++i) {
        array[i] = atomicLongArray.get(i);
      }
      return array;
    }

    
Number of bits /** Number of bits */
    long bitSize() {
      return (long) data.length() * Long.SIZE;
    }

    
Number of set bits (1s).
Note that because of concurrent set calls and uses of atomics, this bitCount is a (very)
close *estimate* of the actual number of bits set. It's not possible to do better than an
estimate without locking. Note that the number, if not exactly accurate, is *always*
underestimating, never overestimating.
/**
     * Number of set bits (1s).
     *
     * <p>Note that because of concurrent set calls and uses of atomics, this bitCount is a (very)
     * close *estimate* of the actual number of bits set. It's not possible to do better than an
     * estimate without locking. Note that the number, if not exactly accurate, is *always*
     * underestimating, never overestimating.
     */
    long bitCount() {
      return bitCount.sum();
    }

    LockFreeBitArray copy() {
      return new LockFreeBitArray(toPlainArray(data));
    }

    
Combines the two BitArrays using bitwise OR.
NOTE: Because of the use of atomics, if the other LockFreeBitArray is being mutated while
this operation is executing, not all of those new 1's may be set in the final state of this
LockFreeBitArray. The ONLY guarantee provided is that all the bits that were set in the other
LockFreeBitArray at the start of this method will be set in this LockFreeBitArray at the end
of this method.
/**
     * Combines the two BitArrays using bitwise OR.
     *
     * <p>NOTE: Because of the use of atomics, if the other LockFreeBitArray is being mutated while
     * this operation is executing, not all of those new 1's may be set in the final state of this
     * LockFreeBitArray. The ONLY guarantee provided is that all the bits that were set in the other
     * LockFreeBitArray at the start of this method will be set in this LockFreeBitArray at the end
     * of this method.
     */
    void putAll(LockFreeBitArray other) {
      checkArgument(
          data.length() == other.data.length(),
          "BitArrays must be of equal length (%s != %s)",
          data.length(),
          other.data.length());
      for (int i = 0; i < data.length(); i++) {
        long otherLong = other.data.get(i);

        long ourLongOld;
        long ourLongNew;
        boolean changedAnyBits = true;
        do {
          ourLongOld = data.get(i);
          ourLongNew = ourLongOld | otherLong;
          if (ourLongOld == ourLongNew) {
            changedAnyBits = false;
            break;
          }
        } while (!data.compareAndSet(i, ourLongOld, ourLongNew));

        if (changedAnyBits) {
          int bitsAdded = Long.bitCount(ourLongNew) - Long.bitCount(ourLongOld);
          bitCount.add(bitsAdded);
        }
      }
    }

    @Override
    public boolean equals(@Nullable Object o) {
      if (o instanceof LockFreeBitArray) {
        LockFreeBitArray lockFreeBitArray = (LockFreeBitArray) o;
        // TODO(lowasser): avoid allocation here
        return Arrays.equals(toPlainArray(data), toPlainArray(lockFreeBitArray.data));
      }
      return false;
    }

    @Override
    public int hashCode() {
      // TODO(lowasser): avoid allocation here
      return Arrays.hashCode(toPlainArray(data));
    }
  }
}