gcc/libjava/java/util/Random.java

/* Copyright (C) 1998, 1999  Cygnus Solutions

   This file is part of libgcj.

This software is copyrighted work licensed under the terms of the
Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
details.  */

package java.util;

import java.io.Serializable;

/**
 * @author Warren Levy <warrenl@cygnus.com>
 * @date August 25, 1998.
 */
/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
 * "The Java Language Specification", ISBN 0-201-63451-1
 * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
 * Status:  Believed complete and correct
 */

/* This class is completely specified by the spec to ensure absolute
 * portability between all implementations of Java 
 */
public class Random implements Serializable
{
  /* Used by next() to hold the state of the pseudorandom number generator */
  protected long seed;

  /* Used by nextGaussian() to hold a precomputed value */
  /* to be delivered by that method the next time it is called */
  protected double nextNextGaussian;

  /* Used by nextGaussian() to keep track of whether it is has precomputed */
  /* and stashed away the next value to be delivered by that method */
  protected boolean haveNextNextGaussian = false;

  public Random()
  {
    this(System.currentTimeMillis());
  }

  public Random(long seed)
  {
    setSeed(seed);
  }

  protected synchronized int next(int bits)
  {
    seed = (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1);
    return (int)(seed >>> (48 - bits));
  }

  // JDK1.2
  public boolean nextBoolean()
  {
    return next(1) != 0;
  }

  /* The method nextBytes() is not fully specified in the published specs.
   * At first I implemented it simply via:
   *	for (int i = 0; i < buf.length; i++)
   *	  buf[i] = (byte)next(8);
   * but a simple test did not yield the same results as the std implementation.
   * There seemed to be a relationship where each i byte above was at pos 4*i+3
   * in the std.  For efficiency, by reducing calls to the expensive math
   * routines, the std probably was calling next(32) once rather than next(8)
   * 4 times.  Changing the algorithm to the one below based on that assumption
   * then yielded identical results to the std.
   */
  public void nextBytes(byte[] buf)
  {
    int randInt = 0;

    for (int i = 0;  i < buf.length;  i++)
      {
	int shift = (i % 4) * 8;
        if (shift == 0)
            randInt = next(32);
        buf[i] = (byte) (randInt >> shift);
      }
  }

  public double nextDouble()
  {
    return (((long)next(26) << 27) + next(27)) / (double)(1L << 53);
  }

  public float nextFloat()
  {
    return next(24) / ((float)(1 << 24));
  }

  public synchronized double nextGaussian()
  {
    if (haveNextNextGaussian)
      {
        haveNextNextGaussian = false;
        return nextNextGaussian;
      }
    else
      {
        double v1, v2, s;
        do
	  { 
            v1 = 2 * nextDouble() - 1;   // between -1.0 and 1.0
            v2 = 2 * nextDouble() - 1;   // between -1.0 and 1.0
            s = v1 * v1 + v2 * v2;
          } while (s >= 1);
        double norm = Math.sqrt(-2 * Math.log(s)/s);
        nextNextGaussian = v2 * norm;
        haveNextNextGaussian = true;
        return v1 * norm;
      }
  }

  public int nextInt()
  {
    return next(32);
  }

  // JDK1.2
  public int nextInt(int n)
  {
    if (n <= 0)
      throw new IllegalArgumentException("n must be positive");

    int bits, val;
    do
      {
        bits = next(31);
        val = bits % n;
      } while (bits - val + (n-1) < 0);
    return val;
  }

  public long nextLong()
  {
    return ((long)next(32) << 32) + next(32);
  }

  public synchronized void setSeed(long seed)
  {
    this.seed = (seed ^ 0x5DEECE66DL) & ((1L << 48) - 1);
    haveNextNextGaussian = false;
  }
}