Java tutorial
/* * 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.math.random; import java.io.Serializable; import org.apache.commons.math.util.FastMath; /** This class implements a powerful pseudo-random number generator * developed by Makoto Matsumoto and Takuji Nishimura during * 1996-1997. * <p>This generator features an extremely long period * (2<sup>19937</sup>-1) and 623-dimensional equidistribution up to 32 * bits accuracy. The home page for this generator is located at <a * href="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html"> * http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html</a>.</p> * <p>This generator is described in a paper by Makoto Matsumoto and * Takuji Nishimura in 1998: <a * href="http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/ARTICLES/mt.pdf">Mersenne * Twister: A 623-Dimensionally Equidistributed Uniform Pseudo-Random * Number Generator</a>, ACM Transactions on Modeling and Computer * Simulation, Vol. 8, No. 1, January 1998, pp 3--30</p> * <p>This class is mainly a Java port of the 2002-01-26 version of * the generator written in C by Makoto Matsumoto and Takuji * Nishimura. Here is their original copyright:</p> * <table border="0" width="80%" cellpadding="10" align="center" bgcolor="#E0E0E0"> * <tr><td>Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura, * All rights reserved.</td></tr> * <tr><td>Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * <ol> * <li>Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer.</li> * <li>Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution.</li> * <li>The names of its contributors may not be used to endorse or promote * products derived from this software without specific prior written * permission.</li> * </ol></td></tr> * <tr><td><strong>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, * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE * USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH * DAMAGE.</strong></td></tr> * </table> * @version $Revision: 990655 $ $Date: 2010-08-29 23:49:40 +0200 (dim. 29 aot 2010) $ * @since 2.0 */ public class MersenneTwister extends BitsStreamGenerator implements Serializable { /** Serializable version identifier. */ private static final long serialVersionUID = 8661194735290153518L; /** Size of the bytes pool. */ private static final int N = 624; /** Period second parameter. */ private static final int M = 397; /** X * MATRIX_A for X = {0, 1}. */ private static final int[] MAG01 = { 0x0, 0x9908b0df }; /** Bytes pool. */ private int[] mt; /** Current index in the bytes pool. */ private int mti; /** Creates a new random number generator. * <p>The instance is initialized using the current time as the * seed.</p> */ public MersenneTwister() { mt = new int[N]; setSeed(System.currentTimeMillis()); } /** Creates a new random number generator using a single int seed. * @param seed the initial seed (32 bits integer) */ public MersenneTwister(int seed) { mt = new int[N]; setSeed(seed); } /** Creates a new random number generator using an int array seed. * @param seed the initial seed (32 bits integers array), if null * the seed of the generator will be related to the current time */ public MersenneTwister(int[] seed) { mt = new int[N]; setSeed(seed); } /** Creates a new random number generator using a single long seed. * @param seed the initial seed (64 bits integer) */ public MersenneTwister(long seed) { mt = new int[N]; setSeed(seed); } /** Reinitialize the generator as if just built with the given int seed. * <p>The state of the generator is exactly the same as a new * generator built with the same seed.</p> * @param seed the initial seed (32 bits integer) */ @Override public void setSeed(int seed) { // we use a long masked by 0xffffffffL as a poor man unsigned int long longMT = seed; mt[0] = (int) longMT; for (mti = 1; mti < N; ++mti) { // See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. // initializer from the 2002-01-09 C version by Makoto Matsumoto longMT = (1812433253l * (longMT ^ (longMT >> 30)) + mti) & 0xffffffffL; mt[mti] = (int) longMT; } } /** Reinitialize the generator as if just built with the given int array seed. * <p>The state of the generator is exactly the same as a new * generator built with the same seed.</p> * @param seed the initial seed (32 bits integers array), if null * the seed of the generator will be related to the current time */ @Override public void setSeed(int[] seed) { if (seed == null) { setSeed(System.currentTimeMillis()); return; } setSeed(19650218); int i = 1; int j = 0; for (int k = FastMath.max(N, seed.length); k != 0; k--) { long l0 = (mt[i] & 0x7fffffffl) | ((mt[i] < 0) ? 0x80000000l : 0x0l); long l1 = (mt[i - 1] & 0x7fffffffl) | ((mt[i - 1] < 0) ? 0x80000000l : 0x0l); long l = (l0 ^ ((l1 ^ (l1 >> 30)) * 1664525l)) + seed[j] + j; // non linear mt[i] = (int) (l & 0xffffffffl); i++; j++; if (i >= N) { mt[0] = mt[N - 1]; i = 1; } if (j >= seed.length) { j = 0; } } for (int k = N - 1; k != 0; k--) { long l0 = (mt[i] & 0x7fffffffl) | ((mt[i] < 0) ? 0x80000000l : 0x0l); long l1 = (mt[i - 1] & 0x7fffffffl) | ((mt[i - 1] < 0) ? 0x80000000l : 0x0l); long l = (l0 ^ ((l1 ^ (l1 >> 30)) * 1566083941l)) - i; // non linear mt[i] = (int) (l & 0xffffffffL); i++; if (i >= N) { mt[0] = mt[N - 1]; i = 1; } } mt[0] = 0x80000000; // MSB is 1; assuring non-zero initial array } /** Reinitialize the generator as if just built with the given long seed. * <p>The state of the generator is exactly the same as a new * generator built with the same seed.</p> * @param seed the initial seed (64 bits integer) */ @Override public void setSeed(long seed) { setSeed(new int[] { (int) (seed >>> 32), (int) (seed & 0xffffffffl) }); } /** Generate next pseudorandom number. * <p>This method is the core generation algorithm. It is used by all the * public generation methods for the various primitive types {@link * #nextBoolean()}, {@link #nextBytes(byte[])}, {@link #nextDouble()}, * {@link #nextFloat()}, {@link #nextGaussian()}, {@link #nextInt()}, * {@link #next(int)} and {@link #nextLong()}.</p> * @param bits number of random bits to produce * @return random bits generated */ @Override protected int next(int bits) { int y; if (mti >= N) { // generate N words at one time int mtNext = mt[0]; for (int k = 0; k < N - M; ++k) { int mtCurr = mtNext; mtNext = mt[k + 1]; y = (mtCurr & 0x80000000) | (mtNext & 0x7fffffff); mt[k] = mt[k + M] ^ (y >>> 1) ^ MAG01[y & 0x1]; } for (int k = N - M; k < N - 1; ++k) { int mtCurr = mtNext; mtNext = mt[k + 1]; y = (mtCurr & 0x80000000) | (mtNext & 0x7fffffff); mt[k] = mt[k + (M - N)] ^ (y >>> 1) ^ MAG01[y & 0x1]; } y = (mtNext & 0x80000000) | (mt[0] & 0x7fffffff); mt[N - 1] = mt[M - 1] ^ (y >>> 1) ^ MAG01[y & 0x1]; mti = 0; } y = mt[mti++]; // tempering y ^= y >>> 11; y ^= (y << 7) & 0x9d2c5680; y ^= (y << 15) & 0xefc60000; y ^= y >>> 18; return y >>> (32 - bits); } }