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Advanced Bloom Filter Based Algorithms for Efficient Approximate Data De-Duplication in Streams
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/*
 * 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.
 */

// @formatter:off
package com.github.jparkie.deduplicator;

/**
 * Copied From: https://github.com/apache/spark/blob/branch-2.0/common/sketch/src/main/java/org/apache/spark/util/sketch/Murmur3_x86_32.java
 *
 * 32-bit Murmur3 hasher.  This is based on Guava's Murmur3_32HashFunction.
 */
public final class Murmur3_x86_32 {
    private static final int C1 = 0xcc9e2d51;
    private static final int C2 = 0x1b873593;

    private final int seed;

    public Murmur3_x86_32(int seed) {
        this.seed = seed;
    }

    @Override
    public String toString() {
        return "Murmur3_32(seed=" + seed + ")";
    }

    public int hashInt(int input) {
        return hashInt(input, seed);
    }

    public static int hashInt(int input, int seed) {
        int k1 = mixK1(input);
        int h1 = mixH1(seed, k1);

        return fmix(h1, 4);
    }

    public int hashUnsafeWords(Object base, long offset, int lengthInBytes) {
        return hashUnsafeWords(base, offset, lengthInBytes, seed);
    }

    public static int hashUnsafeWords(Object base, long offset, int lengthInBytes, int seed) {
        // This is based on Guava's `Murmur32_Hasher.processRemaining(ByteBuffer)` method.
        assert (lengthInBytes % 8 == 0): "lengthInBytes must be a multiple of 8 (word-aligned)";
        int h1 = hashBytesByInt(base, offset, lengthInBytes, seed);
        return fmix(h1, lengthInBytes);
    }

    public static int hashUnsafeBytes(Object base, long offset, int lengthInBytes, int seed) {
        assert (lengthInBytes >= 0): "lengthInBytes cannot be negative";
        int lengthAligned = lengthInBytes - lengthInBytes % 4;
        int h1 = hashBytesByInt(base, offset, lengthAligned, seed);
        for (int i = lengthAligned; i < lengthInBytes; i++) {
            int halfWord = Platform.getByte(base, offset + i);
            int k1 = mixK1(halfWord);
            h1 = mixH1(h1, k1);
        }
        return fmix(h1, lengthInBytes);
    }

    private static int hashBytesByInt(Object base, long offset, int lengthInBytes, int seed) {
        assert (lengthInBytes % 4 == 0);
        int h1 = seed;
        for (int i = 0; i < lengthInBytes; i += 4) {
            int halfWord = Platform.getInt(base, offset + i);
            int k1 = mixK1(halfWord);
            h1 = mixH1(h1, k1);
        }
        return h1;
    }

    public int hashLong(long input) {
        return hashLong(input, seed);
    }

    public static int hashLong(long input, int seed) {
        int low = (int) input;
        int high = (int) (input >>> 32);

        int k1 = mixK1(low);
        int h1 = mixH1(seed, k1);

        k1 = mixK1(high);
        h1 = mixH1(h1, k1);

        return fmix(h1, 8);
    }

    private static int mixK1(int k1) {
        k1 *= C1;
        k1 = Integer.rotateLeft(k1, 15);
        k1 *= C2;
        return k1;
    }

    private static int mixH1(int h1, int k1) {
        h1 ^= k1;
        h1 = Integer.rotateLeft(h1, 13);
        h1 = h1 * 5 + 0xe6546b64;
        return h1;
    }

    // Finalization mix - force all bits of a hash block to avalanche
    private static int fmix(int h1, int length) {
        h1 ^= length;
        h1 ^= h1 >>> 16;
        h1 *= 0x85ebca6b;
        h1 ^= h1 >>> 13;
        h1 *= 0xc2b2ae35;
        h1 ^= h1 >>> 16;
        return h1;
    }
}
// @formatter:on