com.tencent.polaris.plugins.loadbalancer.ringhash.MurmurHash Maven / Gradle / Ivy

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/*
 * Tencent is pleased to support the open source community by making Polaris available.
 *
 * Copyright (C) 2019 THL A29 Limited, a Tencent company. All rights reserved.
 *
 * Licensed under the BSD 3-Clause License (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * https://opensource.org/licenses/BSD-3-Clause
 *
 * 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.tencent.polaris.plugins.loadbalancer.ringhash;

import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

/**
 * Murmur hash策略
 */
public class MurmurHash implements HashStrategy {

    @Override
    public int getHashCode(String origin) {
        ByteBuffer buf = ByteBuffer.wrap(origin.getBytes());
        int seed = 0x1234ABCD;

        buf.order(ByteOrder.LITTLE_ENDIAN);

        long m = 0xc6a4a7935bd1e995L;
        int r = 47;

        long h = seed ^ (buf.remaining() * m);

        long k;
        while (buf.remaining() >= 8) {
            k = buf.getLong();

            k *= m;
            k ^= k >>> r;
            k *= m;

            h ^= k;
            h *= m;
        }

        if (buf.remaining() > 0) {
            ByteBuffer finish = ByteBuffer.allocate(8).order(
                    ByteOrder.LITTLE_ENDIAN);
            // for big-endian version, do this first:
            // finish.position(8-buf.remaining());
            ((Buffer)finish.put(buf)).rewind();
            h ^= finish.getLong();
            h *= m;
        }
        h ^= h >>> r;
        h *= m;
        h ^= h >>> r;

        ByteOrder byteOrder = buf.order();
        buf.order(byteOrder);
        return (int) (h & 0xffffffffL);
    }
}