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Java example source code file (ISAACRandom.java)

This example Java source code file (ISAACRandom.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

bitsstreamgenerator, gld_ratio, h_size, isaacrandom, mask, override, serializable, size, size_l

The ISAACRandom.java Java example source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.math3.random;

import java.io.Serializable;

import org.apache.commons.math3.util.FastMath;

/**
 * <a href="http://burtleburtle.net/bob/rand/isaacafa.html">
 *  ISAAC: a fast cryptographic pseudo-random number generator</a>
 * <br/>
 * ISAAC (Indirection, Shift, Accumulate, Add, and Count) generates 32-bit
 * random numbers.
 * ISAAC has been designed to be cryptographically secure and is inspired
 * by RC4.
 * Cycles are guaranteed to be at least 2<sup>40 values long, and they
 * are 2<sup>8295 values long on average.
 * The results are uniformly distributed, unbiased, and unpredictable unless
 * you know the seed.
 * <br/>
 * This code is based (with minor changes and improvements) on the original
 * implementation of the algorithm by Bob Jenkins.
 * <br/>
 *
 * @since 3.0
 */
public class ISAACRandom extends BitsStreamGenerator implements Serializable {
    /** Serializable version identifier */
    private static final long serialVersionUID = 7288197941165002400L;
    /** Log of size of rsl[] and mem[] */
    private static final int SIZE_L = 8;
    /** Size of rsl[] and mem[] */
    private static final int SIZE = 1 << SIZE_L;
    /** Half-size of rsl[] and mem[] */
    private static final int H_SIZE = SIZE >> 1;
    /** For pseudo-random lookup */
    private static final int MASK = SIZE - 1 << 2;
    /** The golden ratio */
    private static final int GLD_RATIO = 0x9e3779b9;
    /** The results given to the user */
    private final int[] rsl = new int[SIZE];
    /** The internal state */
    private final int[] mem = new int[SIZE];
    /** Count through the results in rsl[] */
    private int count;
    /** Accumulator */
    private int isaacA;
    /** The last result */
    private int isaacB;
    /** Counter, guarantees cycle is at least 2^40 */
    private int isaacC;
    /** Service variable. */
    private final int[] arr = new int[8];
    /** Service variable. */
    private int isaacX;
    /** Service variable. */
    private int isaacI;
    /** Service variable. */
    private int isaacJ;


    /**
     * Creates a new ISAAC random number generator.
     * <br/>
     * The instance is initialized using a combination of the
     * current time and system hash code of the instance as the seed.
     */
    public ISAACRandom() {
        setSeed(System.currentTimeMillis() + System.identityHashCode(this));
    }

    /**
     * Creates a new ISAAC random number generator using a single long seed.
     *
     * @param seed Initial seed.
     */
    public ISAACRandom(long seed) {
        setSeed(seed);
    }

    /**
     * Creates a new ISAAC random number generator using an int array seed.
     *
     * @param seed Initial seed. If {@code null}, the seed will be related
     * to the current time.
     */
    public ISAACRandom(int[] seed) {
        setSeed(seed);
    }

    /** {@inheritDoc} */
    @Override
    public void setSeed(int seed) {
        setSeed(new int[]{seed});
    }

    /** {@inheritDoc} */
    @Override
    public void setSeed(long seed) {
        setSeed(new int[]{(int) (seed >>> 32), (int) (seed & 0xffffffffL)});
    }

    /** {@inheritDoc} */
    @Override
    public void setSeed(int[] seed) {
        if (seed == null) {
            setSeed(System.currentTimeMillis() + System.identityHashCode(this));
            return;
        }
        final int seedLen = seed.length;
        final int rslLen = rsl.length;
        System.arraycopy(seed, 0, rsl, 0, FastMath.min(seedLen, rslLen));
        if (seedLen < rslLen) {
            for (int j = seedLen; j < rslLen; j++) {
                long k = rsl[j - seedLen];
                rsl[j] = (int) (0x6c078965L * (k ^ k >> 30) + j & 0xffffffffL);
            }
        }
        initState();
    }

    /** {@inheritDoc} */
    @Override
    protected int next(int bits) {
        if (count < 0) {
            isaac();
            count = SIZE - 1;
        }
        return rsl[count--] >>> 32 - bits;
    }

    /** Generate 256 results */
    private void isaac() {
        isaacI = 0;
        isaacJ = H_SIZE;
        isaacB += ++isaacC;
        while (isaacI < H_SIZE) {
            isaac2();
        }
        isaacJ = 0;
        while (isaacJ < H_SIZE) {
            isaac2();
        }
    }

    /** Intermediate internal loop. */
    private void isaac2() {
        isaacX = mem[isaacI];
        isaacA ^= isaacA << 13;
        isaacA += mem[isaacJ++];
        isaac3();
        isaacX = mem[isaacI];
        isaacA ^= isaacA >>> 6;
        isaacA += mem[isaacJ++];
        isaac3();
        isaacX = mem[isaacI];
        isaacA ^= isaacA << 2;
        isaacA += mem[isaacJ++];
        isaac3();
        isaacX = mem[isaacI];
        isaacA ^= isaacA >>> 16;
        isaacA += mem[isaacJ++];
        isaac3();
    }

    /** Lowest level internal loop. */
    private void isaac3() {
        mem[isaacI] = mem[(isaacX & MASK) >> 2] + isaacA + isaacB;
        isaacB = mem[(mem[isaacI] >> SIZE_L & MASK) >> 2] + isaacX;
        rsl[isaacI++] = isaacB;
    }

    /** Initialize, or reinitialize, this instance of rand. */
    private void initState() {
        isaacA = 0;
        isaacB = 0;
        isaacC = 0;
        for (int j = 0; j < arr.length; j++) {
            arr[j] = GLD_RATIO;
        }
        for (int j = 0; j < 4; j++) {
            shuffle();
        }
        // fill in mem[] with messy stuff
        for (int j = 0; j < SIZE; j += 8) {
            arr[0] += rsl[j];
            arr[1] += rsl[j + 1];
            arr[2] += rsl[j + 2];
            arr[3] += rsl[j + 3];
            arr[4] += rsl[j + 4];
            arr[5] += rsl[j + 5];
            arr[6] += rsl[j + 6];
            arr[7] += rsl[j + 7];
            shuffle();
            setState(j);
        }
        // second pass makes all of seed affect all of mem
        for (int j = 0; j < SIZE; j += 8) {
            arr[0] += mem[j];
            arr[1] += mem[j + 1];
            arr[2] += mem[j + 2];
            arr[3] += mem[j + 3];
            arr[4] += mem[j + 4];
            arr[5] += mem[j + 5];
            arr[6] += mem[j + 6];
            arr[7] += mem[j + 7];
            shuffle();
            setState(j);
        }
        isaac();
        count = SIZE - 1;
        clear();
    }

    /** Shuffle array. */
    private void shuffle() {
        arr[0] ^= arr[1] << 11;
        arr[3] += arr[0];
        arr[1] += arr[2];
        arr[1] ^= arr[2] >>> 2;
        arr[4] += arr[1];
        arr[2] += arr[3];
        arr[2] ^= arr[3] << 8;
        arr[5] += arr[2];
        arr[3] += arr[4];
        arr[3] ^= arr[4] >>> 16;
        arr[6] += arr[3];
        arr[4] += arr[5];
        arr[4] ^= arr[5] << 10;
        arr[7] += arr[4];
        arr[5] += arr[6];
        arr[5] ^= arr[6] >>> 4;
        arr[0] += arr[5];
        arr[6] += arr[7];
        arr[6] ^= arr[7] << 8;
        arr[1] += arr[6];
        arr[7] += arr[0];
        arr[7] ^= arr[0] >>> 9;
        arr[2] += arr[7];
        arr[0] += arr[1];
    }

    /** Set the state by copying the internal arrays.
     *
     * @param start First index into {@link #mem} array.
     */
    private void setState(int start) {
        mem[start] = arr[0];
        mem[start + 1] = arr[1];
        mem[start + 2] = arr[2];
        mem[start + 3] = arr[3];
        mem[start + 4] = arr[4];
        mem[start + 5] = arr[5];
        mem[start + 6] = arr[6];
        mem[start + 7] = arr[7];
    }
}

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