JDK14/Java14源码在线阅读

/*
 *
 * Copyright (c) 2007, Oracle and/or its affiliates. All rights reserved.
 *
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 * modification, are permitted provided that the following conditions
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 *
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 *
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 *
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 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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 */



import java.util.Random;

/**
 * An object that implements a cheesy pseudorandom permutation of the integers
 * from zero to some user-specified value. (The permutation is a linear
 * function.)
 *
 * @author Josh Bloch
 */
class Permuter {
    /**
     * The size of the permutation.
     */
    private int modulus;

    /**
     * Nonnegative integer less than n that is relatively prime to m.
     */
    private int multiplier;

    /**
     * Pseudorandom nonnegative integer less than n.
     */
    private int addend = 22;

    public Permuter(int n) {
        if (n<0) {
            throw new IllegalArgumentException();
        }
        modulus = n;
        if (n==1) {
            return;
        }

        // Initialize the multiplier and offset
        multiplier = (int) Math.sqrt(n);
        while (gcd(multiplier, n) != 1) {
            if (++multiplier == n) {
                multiplier = 1;
            }
        }
    }

    /**
     * Returns the integer to which this permuter maps the specified integer.
     * The specified integer must be between 0 and n-1, and the returned
     * integer will be as well.
     */
    public int map(int i) {
        return (multiplier * i + addend) % modulus;
    }

    /**
     * Calculate GCD of a and b, which are assumed to be non-negative.
     */
    private static int gcd(int a, int b) {
        while(b != 0) {
            int tmp = a % b;
            a = b;
            b = tmp;
        }
        return a;
    }

    /**

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