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/* |
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* Copyright 1995-2007 Sun Microsystems, Inc. All Rights Reserved. |
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* Copyright (c) 1995, 2010, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Sun designates this |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Sun in the LICENSE file that accompanied this code. |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
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* CA 95054 USA or visit www.sun.com if you need additional information or |
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* have any questions. |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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package java.util; |
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* An instance of this class is used to generate a stream of |
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* pseudorandom numbers. The class uses a 48-bit seed, which is |
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* modified using a linear congruential formula. (See Donald Knuth, |
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* <i>The Art of Computer Programming, Volume 3</i>, Section 3.2.1.) |
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* <i>The Art of Computer Programming, Volume 2</i>, Section 3.2.1.) |
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* <p> |
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* If two instances of {@code Random} are created with the same |
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* seed, and the same sequence of method calls is made for each, they |
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* <p> |
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* Many applications will find the method {@link Math#random} simpler to use. |
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* |
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* <p>Instances of {@code java.util.Random} are threadsafe. |
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* However, the concurrent use of the same {@code java.util.Random} |
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* instance across threads may encounter contention and consequent |
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* poor performance. Consider instead using |
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* {@link java.util.concurrent.ThreadLocalRandom} in multithreaded |
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* designs. |
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* |
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* <p>Instances of {@code java.util.Random} are not cryptographically |
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* secure. Consider instead using {@link java.security.SecureRandom} to |
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* get a cryptographically secure pseudo-random number generator for use |
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* by security-sensitive applications. |
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* |
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* @author Frank Yellin |
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* @since 1.0 |
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*/ |
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*/ |
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private final AtomicLong seed; |
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private final static long multiplier = 0x5DEECE66DL; |
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private final static long addend = 0xBL; |
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private final static long mask = (1L << 48) - 1; |
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private static final long multiplier = 0x5DEECE66DL; |
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private static final long addend = 0xBL; |
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private static final long mask = (1L << 48) - 1; |
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/** |
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* Creates a new random number generator. This constructor sets |
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* the seed of the random number generator to a value very likely |
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* to be distinct from any other invocation of this constructor. |
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*/ |
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public Random() { this(++seedUniquifier + System.nanoTime()); } |
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private static volatile long seedUniquifier = 8682522807148012L; |
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public Random() { |
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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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for (;;) { |
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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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private static final AtomicLong seedUniquifier |
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= new AtomicLong(8682522807148012L); |
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/** |
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* Creates a new random number generator using a single {@code long} seed. |
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* @see #setSeed(long) |
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*/ |
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public Random(long seed) { |
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this.seed = new AtomicLong(0L); |
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setSeed(seed); |
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if (getClass() == Random.class) |
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this.seed = new AtomicLong(initialScramble(seed)); |
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else { |
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// subclass might have overridden setSeed |
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this.seed = new AtomicLong(); |
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setSeed(seed); |
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} |
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} |
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|
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private static long initialScramble(long seed) { |
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return (seed ^ multiplier) & mask; |
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} |
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/** |
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* @param seed the initial seed |
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*/ |
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synchronized public void setSeed(long seed) { |
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seed = (seed ^ multiplier) & mask; |
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this.seed.set(seed); |
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this.seed.set(initialScramble(seed)); |
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haveNextNextGaussian = false; |
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} |
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|
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* @return the next pseudorandom, uniformly distributed {@code int} |
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* value between {@code 0} (inclusive) and {@code n} (exclusive) |
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* from this random number generator's sequence |
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* @exception IllegalArgumentException if n is not positive |
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* @throws IllegalArgumentException if n is not positive |
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* @since 1.2 |
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*/ |
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