src/demo/share/jfc/SwingSet2/Permuter.java
author prr
Fri, 23 Mar 2018 13:43:39 -0700
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8198990: Move SwingSet2 from closed to OpenJDK Reviewed-by: serb, jeff, kaddepalli
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/*
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 *
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 * Copyright (c) 2007, Oracle and/or its affiliates. All rights reserved.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 *
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 *   - Redistributions of source code must retain the above copyright
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 *     notice, this list of conditions and the following disclaimer.
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 *
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 *   - Redistributions in binary form must reproduce the above copyright
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 *     notice, this list of conditions and the following disclaimer in the
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 *     documentation and/or other materials provided with the distribution.
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 *
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 *   - Neither the name of Oracle nor the names of its
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 *     contributors may be used to endorse or promote products derived
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 *     from this software without specific prior written permission.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */
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import java.util.Random;
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/**
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 * An object that implements a cheesy pseudorandom permutation of the integers
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 * from zero to some user-specified value. (The permutation is a linear
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 * function.)
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 *
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 * @author Josh Bloch
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 */
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class Permuter {
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    /**
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     * The size of the permutation.
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     */
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    private int modulus;
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    /**
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     * Nonnegative integer less than n that is relatively prime to m.
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     */
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    private int multiplier;
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    /**
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     * Pseudorandom nonnegative integer less than n.
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     */
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    private int addend = 22;
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    public Permuter(int n) {
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        if (n<0) {
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            throw new IllegalArgumentException();
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        }
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        modulus = n;
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        if (n==1) {
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            return;
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        }
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        // Initialize the multiplier and offset
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        multiplier = (int) Math.sqrt(n);
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        while (gcd(multiplier, n) != 1) {
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            if (++multiplier == n) {
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                multiplier = 1;
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            }
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        }
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    }
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    /**
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     * Returns the integer to which this permuter maps the specified integer.
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     * The specified integer must be between 0 and n-1, and the returned
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     * integer will be as well.
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     */
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    public int map(int i) {
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        return (multiplier * i + addend) % modulus;
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    }
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    /**
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     * Calculate GCD of a and b, which are assumed to be non-negative.
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     */
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    private static int gcd(int a, int b) {
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        while(b != 0) {
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            int tmp = a % b;
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            a = b;
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            b = tmp;
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        }
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        return a;
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    }
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    /**
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     * Simple test.  Takes modulus on command line and prints out permutation.
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     */
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    public static void main(String[] args) {
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        int modulus = Integer.parseInt(args[0]);
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        Permuter p = new Permuter(modulus);
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        for (int i=0; i<modulus; i++) {
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            System.out.print(p.map(i)+" ");
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        }
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        System.out.println();
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    }
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}