RandomUtil.java Source code

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Here is the source code for RandomUtil.java

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/*
 * @(#)RandomUtil.java   1.0 Apr 26, 2008
 *
 *   The MIT License
 *
 *   Copyright (c) 2008 Malachi de AElfweald <malachid@gmail.com>
 *
 *   Permission is hereby granted, free of charge, to any person obtaining a copy
 *   of this software and associated documentation files (the "Software"), to deal
 *   in the Software without restriction, including without limitation the rights
 *   to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *   copies of the Software, and to permit persons to whom the Software is
 *   furnished to do so, subject to the following conditions:
 *
 *   The above copyright notice and this permission notice shall be included in
 *   all copies or substantial portions of the Software.
 *
 *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *   AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *   LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *   OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 *   THE SOFTWARE.
 */
//package org.eoti.math;

import java.math.BigInteger;
import java.util.Date;
import java.util.Random;
import java.util.concurrent.locks.ReentrantLock;

public class RandomUtil {
    protected static ReentrantLock singletonLock = new ReentrantLock();
    protected static RandomUtil singleton;

    public static RandomUtil getInstance() {
        // If singleton != null, then just return it (don't lock READ)
        if (singleton == null) {
            // don't let more that one person create the singleton
            singletonLock.lock();

            // if we were waiting for a lock, then someone else already made it
            if (singleton == null)
                singleton = new RandomUtil();

            singletonLock.unlock();
        }

        return singleton;
    }

    protected RandomUtil() {
        random = new Random((new Date()).getTime());
    }

    protected Random random;

    public static int randInt(int maxNumExclusive) {
        return getInstance().random.nextInt(maxNumExclusive);
    }

    public static BigInteger randomBitFlip(BigInteger n) {
        if (n.equals(BigInteger.ONE))
            return BigInteger.ONE;
        if (n.equals(BigInteger.ZERO))
            return BigInteger.ZERO;

        BigInteger toRet = BigInteger.ONE;
        while (toRet.equals(BigInteger.ONE) || toRet.equals(BigInteger.ZERO)) {
            byte[] bytes = n.toByteArray();
            getInstance().random.nextBytes(bytes);
            // could allow up to maxExclusive by converting and checking value
            // but this is faster, even if it doesn't give us full range
            bytes[0] = 0;
            toRet = new BigInteger(bytes);
        }
        return toRet;
    }
}