BasePRNG.java

package gnu.crypto.prng;

// ----------------------------------------------------------------------------
// Copyright (C) 2001, 2002, Free Software Foundation, Inc.
//
// This file is part of GNU Crypto.
//
// GNU Crypto 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, or (at your option)
// any later version.
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
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// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
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// ----------------------------------------------------------------------------

import java.util.Map;

/**
 * <p>An abstract class to facilitate implementing PRNG algorithms.</p>
 *
 * @version $Revision: 1.12 $
 */
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
  {
    return super.clone();
  }

   public abstract void setup(Map attributes);

   public abstract void fillBlock() throws LimitReachedException;
}