baseprng.java

来自「linux下建立JAVA虚拟机的源码KAFFE」· Java 代码 · 共 200 行

/* BasePRNG.java -- 
   Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version.  */


package gnu.java.security.prng;

import java.util.Map;

/**
 * <p>An abstract class to facilitate implementing PRNG algorithms.</p>
 */
public abstract class BasePRNG implements IRandom
{

  // Constants and variables
  // -------------------------------------------------------------------------

  /** The canonical name prefix of the PRNG algorithm. */
  protected String name;

  /** Indicate if this instance has already been initialised or not. */
  protected boolean initialised;

  /** A temporary buffer to serve random bytes. */
  protected byte[] buffer;

  /** The index into buffer of where the next byte will come from. */
  protected int ndx;

  // Constructor(s)
  // -------------------------------------------------------------------------

  /**
   * <p>Trivial constructor for use by concrete subclasses.</p>
   *
   * @param name the canonical name of this instance.
   */
  protected BasePRNG(String name)
  {
    super();

    this.name = name;
    initialised = false;
    buffer = new byte[0];
  }

  // Class methods
  // -------------------------------------------------------------------------

  // Instance methods
  // -------------------------------------------------------------------------

  // IRandom interface implementation ----------------------------------------

  public String name()
  {
    return name;
  }

  public void init(Map attributes)
  {
    this.setup(attributes);

    ndx = 0;
    initialised = true;
  }

  public byte nextByte() throws IllegalStateException, LimitReachedException
  {
    if (!initialised)
      {
        throw new IllegalStateException();
      }
    return nextByteInternal();
  }

  public void nextBytes(byte[] out) throws IllegalStateException,
      LimitReachedException
  {
    nextBytes(out, 0, out.length);
  }

  public void nextBytes(byte[] out, int offset, int length)
      throws IllegalStateException, LimitReachedException
  {
    if (!initialised)
      throw new IllegalStateException("not initialized");

    if (length == 0)
      return;

    if (offset < 0 || length < 0 || offset + length > out.length)
      throw new ArrayIndexOutOfBoundsException("offset=" + offset + " length="
                                               + length + " limit="
                                               + out.length);

    if (ndx >= buffer.length)
      {
        fillBlock();
        ndx = 0;
      }
    int count = 0;
    while (count < length)
      {
        int amount = Math.min(buffer.length - ndx, length - count);
        System.arraycopy(buffer, ndx, out, offset + count, amount);
        count += amount;
        ndx += amount;
        if (ndx >= buffer.length)
          {
            fillBlock();
            ndx = 0;
          }
      }
  }

  public void addRandomByte(byte b)
  {
    throw new UnsupportedOperationException("random state is non-modifiable");
  }

  public void addRandomBytes(byte[] buffer)
  {
    addRandomBytes(buffer, 0, buffer.length);
  }

  public void addRandomBytes(byte[] buffer, int offset, int length)
  {
    throw new UnsupportedOperationException("random state is non-modifiable");
  }

  // Instance methods
  // -------------------------------------------------------------------------

  public boolean isInitialised()
  {
    return initialised;
  }

  private byte nextByteInternal() throws LimitReachedException
  {
    if (ndx >= buffer.length)
      {
        this.fillBlock();
        ndx = 0;
      }

    return buffer[ndx++];
  }

  // abstract methods to implement by subclasses -----------------------------

  public Object clone() throws CloneNotSupportedException
  {
    BasePRNG result = (BasePRNG) super.clone();
    if (this.buffer != null)
      result.buffer = (byte[]) this.buffer.clone();

    return result;
  }

  public abstract void setup(Map attributes);

  public abstract void fillBlock() throws LimitReachedException;
}