mirror of
https://github.com/GTNewHorizons/StructureLib.git
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281 lines
9.4 KiB
Java
281 lines
9.4 KiB
Java
package com.gtnewhorizon.structurelib.util;
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/*
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A subclass of java.util.random that implements the Xorshift random number
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generator
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<p>
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- it is 30% faster than the generator from Java's library - it produces
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random sequences of higher quality than java.util.Random - this class also
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provides a clone() function
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<p>
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Usage: XSRandom rand = new XSRandom(); //Instantiation x = rand.nextInt();
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//pull a random number
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<p>
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To use the class in legacy code, you may also instantiate an XSRandom object
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and assign it to a java.util.Random object: java.util.Random rand = new
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XSRandom();
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<p>
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for an explanation of the algorithm, see
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http://demesos.blogspot.com/2011/09/pseudo-random-number-generators.html
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@author Wilfried Elmenreich University of Klagenfurt/Lakeside Labs
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* http://www.elmenreich.tk
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* <p>
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* This code is released under the GNU Lesser General Public License Version 3
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* http://www.gnu.org/licenses/lgpl-3.0.txt
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*/
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import java.util.Random;
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import java.util.concurrent.atomic.AtomicLong;
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/**
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* XSTR - Xorshift ThermiteRandom
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* Modified by Bogdan-G
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* 03.06.2016
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* version 0.0.4
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*/
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public class XSTR extends Random {
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private static final long serialVersionUID = 6208727693524452904L;
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private long seed;
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private static final long GAMMA = 0x9e3779b97f4a7c15L;
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private static final int PROBE_INCREMENT = 0x9e3779b9;
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private static final long SEEDER_INCREMENT = 0xbb67ae8584caa73bL;
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private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53)
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private static final float FLOAT_UNIT = 0x1.0p-24f; // 1.0f / (1 << 24)
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private static final AtomicLong seedUniquifier = new AtomicLong(8682522807148012L);
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public static final XSTR XSTR_INSTANCE = new XSTR() {
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@Override
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public synchronized void setSeed(long seed) {
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if (!Thread.currentThread().getStackTrace()[2].getClassName().equals(Random.class.getName())) {
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throw new NoSuchMethodError("This is meant to be shared!, leave seed state alone!");
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}
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}
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};
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/*
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MODIFIED BY: Robotia
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Modification: Implemented Random class seed generator
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*/
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/**
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* Creates a new pseudo random number generator. The seed is initialized to
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* the current time, as if by
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* <code>setSeed(System.currentTimeMillis());</code>.
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*/
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public XSTR() {
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this(seedUniquifier() ^ System.nanoTime());
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}
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private static long seedUniquifier() {
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// L'Ecuyer, "Tables of Linear Congruential Generators of
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// Different Sizes and Good Lattice Structure", 1999
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while (true) {
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long current = seedUniquifier.get();
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long next = current * 181783497276652981L;
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if (seedUniquifier.compareAndSet(current, next)) {
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return next;
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}
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}
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}
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/**
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* Creates a new pseudo random number generator, starting with the specified
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* seed, using <code>setSeed(seed);</code>.
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*
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* @param seed the initial seed
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*/
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public XSTR(long seed) {
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this.seed = seed;
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}
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@Override
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public boolean nextBoolean() {
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return next(1) != 0;
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}
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@Override
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public double nextDouble() {
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return (((long) next(26) << 27) + next(27)) * DOUBLE_UNIT;
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}
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/**
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* Returns the current state of the seed, can be used to clone the object
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*
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* @return the current seed
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*/
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public synchronized long getSeed() {
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return seed;
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}
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/**
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* Sets the seed for this pseudo random number generator. As described
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* above, two instances of the same random class, starting with the same
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* seed, produce the same results, if the same methods are called.
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*
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* @param seed the new seed
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*/
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@Override
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public synchronized void setSeed(long seed) {
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this.seed = seed;
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}
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/**
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* @return Returns an XSRandom object with the same state as the original
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*/
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@Override
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public XSTR clone() {
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return new XSTR(getSeed());
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}
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/**
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* Implementation of George Marsaglia's elegant Xorshift random generator
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* 30% faster and better quality than the built-in java.util.random see also
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* see http://www.javamex.com/tutorials/random_numbers/xorshift.shtml
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*
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* @param nbits will shift nbits bits
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* @return next seed
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*/
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@Override
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public int next(int nbits) {
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long x = seed;
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x ^= x << 21;
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x ^= x >>> 35;
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x ^= x << 4;
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seed = x;
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x &= (1L << nbits) - 1;
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return (int) x;
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}
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private boolean haveNextNextGaussian = false;
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private double nextNextGaussian = 0;
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@Override
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public synchronized double nextGaussian() {
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// See Knuth, ACP, Section 3.4.1 Algorithm C.
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if (haveNextNextGaussian) {
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haveNextNextGaussian = false;
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return nextNextGaussian;
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} else {
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double v1, v2, vs;
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do {
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v1 = 2 * nextDouble() - 1; // between -1 and 1
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v2 = 2 * nextDouble() - 1; // between -1 and 1
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vs = v1 * v1 + v2 * v2;
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} while (vs >= 1 || vs == 0);
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double multiplier = StrictMath.sqrt(-2 * StrictMath.log(vs) / vs);
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nextNextGaussian = v2 * multiplier;
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haveNextNextGaussian = true;
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return v1 * multiplier;
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}
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}
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/**
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* Returns a pseudorandom, uniformly distributed {@code int} value between 0
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* (inclusive) and the specified value (exclusive), drawn from this random
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* number generator's sequence. The general contract of {@code nextInt} is
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* that one {@code int} value in the specified range is pseudorandomly
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* generated and returned. All {@code bound} possible {@code int} values are
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* produced with (approximately) equal probability. The method
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* {@code nextInt(int bound)} is implemented by class {@code Random} as if
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* by:
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* <pre> {@code
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* public int nextInt(int bound) {
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* if (bound <= 0)
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* throw new IllegalArgumentException("bound must be positive");
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*
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* if ((bound & -bound) == bound) // i.e., bound is a power of 2
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* return (int)((bound * (long)next(31)) >> 31);
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*
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* int bits, val;
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* do {
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* bits = next(31);
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* val = bits % bound;
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* } while (bits - val + (bound-1) < 0);
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* return val;
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* }}</pre>
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*
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* <p>The hedge "approx
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* imately" is used in the foregoing description only because the next
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* method is only approximately an unbiased source of independently chosen
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* bits. If it were a perfect source of randomly chosen bits, then the
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* algorithm shown would choose {@code int} values from the stated range
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* with perfect uniformity.
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* <p>
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* The algorithm is slightly tricky. It rejects values that would result in
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* an uneven distribution (due to the fact that 2^31 is not divisible by n).
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* The probability of a value being rejected depends on n. The worst case is
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* n=2^30+1, for which the probability of a reject is 1/2, and the expected
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* number of iterations before the loop terminates is 2.
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* <p>
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* The algorithm treats the case where n is a power of two specially: it
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* returns the correct number of high-order bits from the underlying
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* pseudo-random number generator. In the absence of special treatment, the
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* correct number of <i>low-order</i> bits would be returned. Linear
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* congruential pseudo-random number generators such as the one implemented
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* by this class are known to have short periods in the sequence of values
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* of their low-order bits. Thus, this special case greatly increases the
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* length of the sequence of values returned by successive calls to this
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* method if n is a small power of two.
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*
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* @param bound the upper bound (exclusive). Must be positive.
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* @return the next pseudorandom, uniformly distributed {@code int} value
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* between zero (inclusive) and {@code bound} (exclusive) from this random
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* number generator's sequence
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* @throws IllegalArgumentException if bound is not positive
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* @since 1.2
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*/
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@Override
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public int nextInt(int bound) {
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// if (bound <= 0) {
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// throw new RuntimeException("BadBound");
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// }
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/*int r = next(31);
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int m = bound - 1;
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if ((bound & m) == 0) // i.e., bound is a power of 2
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{
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r = (int) ((bound * (long) r) >> 31);
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} else {
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for (int u = r;
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u - (r = u % bound) + m < 0;
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u = next(31))
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;
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}
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return r;*/
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// speedup, new nextInt ~+40%
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long last = seed ^ seed << 21;
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last ^= last >>> 35;
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last ^= last << 4;
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seed = last;
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int out = (int) last % bound;
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return out < 0 ? -out : out;
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}
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@Override
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public int nextInt() {
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return next(32);
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}
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@Override
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public float nextFloat() {
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return next(24) * FLOAT_UNIT;
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}
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@Override
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public long nextLong() {
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// it's okay that the bottom word remains signed.
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return ((long) next(32) << 32) + next(32);
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}
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@Override
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public void nextBytes(byte[] bytes_arr) {
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for (int iba = 0, lenba = bytes_arr.length; iba < lenba; ) {
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for (int rndba = nextInt(), nba = Math.min(lenba - iba, Integer.SIZE / Byte.SIZE);
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nba-- > 0;
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rndba >>= Byte.SIZE) {
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bytes_arr[iba++] = (byte) rndba;
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}
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}
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}
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}
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