org.lealone.plugins.mysql.server.util.RandomUtil Maven / Gradle / Ivy

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/*
 * Copyright 1999-2012 Alibaba Group.
 *  
 * 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 org.lealone.plugins.mysql.server.util;

/**
 * @author xianmao.hexm 2010-1-21 上午10:39:54
 */
public final class RandomUtil {

    private static final byte[] bytes = {
            '1',
            '2',
            '3',
            '4',
            '5',
            '6',
            '7',
            '8',
            '9',
            '0',
            'q',
            'w',
            'e',
            'r',
            't',
            'y',
            'u',
            'i',
            'o',
            'p',
            'a',
            's',
            'd',
            'f',
            'g',
            'h',
            'j',
            'k',
            'l',
            'z',
            'x',
            'c',
            'v',
            'b',
            'n',
            'm',
            'Q',
            'W',
            'E',
            'R',
            'T',
            'Y',
            'U',
            'I',
            'O',
            'P',
            'A',
            'S',
            'D',
            'F',
            'G',
            'H',
            'J',
            'K',
            'L',
            'Z',
            'X',
            'C',
            'V',
            'B',
            'N',
            'M' };

    private static final long multiplier = 0x5DEECE66DL;
    private static final long addend = 0xBL;
    private static final long mask = (1L << 48) - 1;
    private static final long integerMask = (1L << 33) - 1;
    private static final long seedUniquifier = 8682522807148012L;

    private static long seed;
    static {
        long s = seedUniquifier + System.nanoTime();
        s = (s ^ multiplier) & mask;
        seed = s;
    }

    public static byte[] randomBytes(int size) {
        byte[] bb = bytes;
        byte[] ab = new byte[size];
        for (int i = 0; i < size; i++) {
            ab[i] = randomByte(bb);
        }
        return ab;
    }

    private static byte randomByte(byte[] b) {
        int ran = (int) ((next() & integerMask) >>> 16);
        return b[ran % b.length];
    }

    private static long next() {
        long oldSeed = seed;
        long nextSeed = 0L;
        do {
            nextSeed = (oldSeed * multiplier + addend) & mask;
        } while (oldSeed == nextSeed);
        seed = nextSeed;
        return nextSeed;
    }
}