149 lines
3.7 KiB
Java
149 lines
3.7 KiB
Java
/* Copyright (C) 1998, 1999 Cygnus Solutions
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This file is part of libgcj.
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This software is copyrighted work licensed under the terms of the
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Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
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details. */
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package java.util;
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import java.io.Serializable;
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/**
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* @author Warren Levy <warrenl@cygnus.com>
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* @date August 25, 1998.
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*/
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/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
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* "The Java Language Specification", ISBN 0-201-63451-1
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* plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
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* Status: Believed complete and correct
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*/
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/* This class is completely specified by the spec to ensure absolute
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* portability between all implementations of Java
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*/
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public class Random implements Serializable
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{
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/* Used by next() to hold the state of the pseudorandom number generator */
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protected long seed;
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/* Used by nextGaussian() to hold a precomputed value */
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/* to be delivered by that method the next time it is called */
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protected double nextNextGaussian;
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/* Used by nextGaussian() to keep track of whether it is has precomputed */
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/* and stashed away the next value to be delivered by that method */
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protected boolean haveNextNextGaussian = false;
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public Random()
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{
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this(System.currentTimeMillis());
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}
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public Random(long seed)
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{
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setSeed(seed);
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}
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protected synchronized int next(int bits)
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{
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seed = (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1);
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return (int)(seed >>> (48 - bits));
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}
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// JDK1.2
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public boolean nextBoolean()
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{
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return next(1) != 0;
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}
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/* The method nextBytes() is not fully specified in the published specs.
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* At first I implemented it simply via:
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* for (int i = 0; i < buf.length; i++)
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* buf[i] = (byte)next(8);
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* but a simple test did not yield the same results as the std implementation.
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* There seemed to be a relationship where each i byte above was at pos 4*i+3
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* in the std. For efficiency, by reducing calls to the expensive math
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* routines, the std probably was calling next(32) once rather than next(8)
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* 4 times. Changing the algorithm to the one below based on that assumption
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* then yielded identical results to the std.
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*/
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public void nextBytes(byte[] buf)
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{
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int randInt = 0;
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for (int i = 0; i < buf.length; i++)
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{
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int shift = (i % 4) * 8;
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if (shift == 0)
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randInt = next(32);
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buf[i] = (byte) (randInt >> shift);
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}
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}
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public double nextDouble()
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{
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return (((long)next(26) << 27) + next(27)) / (double)(1L << 53);
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}
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public float nextFloat()
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{
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return next(24) / ((float)(1 << 24));
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}
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public synchronized double nextGaussian()
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{
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if (haveNextNextGaussian)
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{
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haveNextNextGaussian = false;
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return nextNextGaussian;
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}
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else
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{
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double v1, v2, s;
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do
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{
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v1 = 2 * nextDouble() - 1; // between -1.0 and 1.0
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v2 = 2 * nextDouble() - 1; // between -1.0 and 1.0
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s = v1 * v1 + v2 * v2;
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} while (s >= 1);
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double norm = Math.sqrt(-2 * Math.log(s)/s);
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nextNextGaussian = v2 * norm;
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haveNextNextGaussian = true;
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return v1 * norm;
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}
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}
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public int nextInt()
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{
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return next(32);
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}
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// JDK1.2
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public int nextInt(int n)
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{
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if (n <= 0)
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throw new IllegalArgumentException("n must be positive");
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int bits, val;
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do
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{
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bits = next(31);
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val = bits % n;
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} while (bits - val + (n-1) < 0);
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return val;
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}
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public long nextLong()
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{
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return ((long)next(32) << 32) + next(32);
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}
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public synchronized void setSeed(long seed)
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{
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this.seed = (seed ^ 0x5DEECE66DL) & ((1L << 48) - 1);
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haveNextNextGaussian = false;
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}
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}
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