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/* 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;

/**

 * An abstract class to facilitate implementing PRNG algorithms.

 */

public abstract class BasePRNG

    implements IRandom

{

  /** 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;

  /**

   * Trivial constructor for use by concrete subclasses.

   *

   * @param name the canonical name of this instance.

   */

  protected BasePRNG(String name)

  {

    super();

    this.name = name;

    initialised = false;

    buffer = new byte[0];

  }

  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");

  }

  public boolean isInitialised()

  {

    return initialised;

  }

  private byte nextByteInternal() throws LimitReachedException

  {

    if (ndx >= buffer.length)

      {

        this.fillBlock();

        ndx = 0;

      }

    return buffer[ndx++];

  }

  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;

}