/*
* 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;
/**
* 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
* @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).
*/
MURMUR128_MITZ_32() {
@Override public <T> boolean put(T object, Funnel<? super T> funnel,
int numHashFunctions, BitArray 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, BitArray 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 {@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, BitArray 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, BitArray 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]);
}
};
// Note: We use this instead of java.util.BitSet because we need access to the long[] data field
static final class BitArray {
final long[] data;
long bitCount;
BitArray(long bits) {
this(new long[Ints.checkedCast(LongMath.divide(bits, 64, RoundingMode.CEILING))]);
}
// Used by serialization
BitArray(long[] data) {
checkArgument(data.length > 0, "data length is zero!");
this.data = data;
long bitCount = 0;
for (long value : data) {
bitCount += Long.bitCount(value);
}
this.bitCount = bitCount;
}
/** Returns true if the bit changed value. */
boolean set(long index) {
if (!get(index)) {
data[(int) (index >>> 6)] |= (1L << index);
bitCount++;
return true;
}
return false;
}
boolean get(long index) {
return (data[(int) (index >>> 6)] & (1L << index)) != 0;
}
/** Number of bits */
long bitSize() {
return (long) data.length * Long.SIZE;
}
/** Number of set bits (1s) */
long bitCount() {
return bitCount;
}
BitArray copy() {
return new BitArray(data.clone());
}
/** Combines the two BitArrays using bitwise OR. */
void putAll(BitArray array) {
checkArgument(data.length == array.data.length,
"BitArrays must be of equal length (%s != %s)", data.length, array.data.length);
bitCount = 0;
for (int i = 0; i < data.length; i++) {
data[i] |= array.data[i];
bitCount += Long.bitCount(data[i]);
}
}
@Override public boolean equals(Object o) {
if (o instanceof BitArray) {
BitArray bitArray = (BitArray) o;
return Arrays.equals(data, bitArray.data);
}
return false;
}
@Override public int hashCode() {
return Arrays.hashCode(data);
}
}
}