gt:     if (numBits == 0)
context: /* SecureRandom.java --- Secure Random class implementation
     Copyright (C) 1999, 2001, 2002, 2003 Free Software Foundation, Inc.
  
  This file is 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, 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; see the file COPYING.  If not, write to the
  Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  02111-1307 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 java.security;
  
  import gnu.java.security.Engine;
  
  import java.util.Enumeration;
  import java.util.Random;
  
  /**
   * An interface to a cryptographically secure pseudo-random number
   * generator (PRNG). Random (or at least unguessable) numbers are used
   * in all areas of security and cryptography, from the generation of
   * keys and initialization vectors to the generation of random padding
   * bytes.
   *
   * @author Mark Benvenuto <ivymccough@worldnet.att.net>
   * @author Casey Marshall
   */
  public class SecureRandom extends Random
  {
  
    // Constants and fields.
    // ------------------------------------------------------------------------
  
    /** Service name for PRNGs. */
    private static final String SECURE_RANDOM = "SecureRandom";
  
    private static final long serialVersionUID = 4940670005562187L;
  
    //Serialized Field
    long counter = 0;		//Serialized
    Provider provider = null;
    byte[] randomBytes = null;	//Always null
    int randomBytesUsed = 0;
    SecureRandomSpi secureRandomSpi = null;
    byte[] state = null;
  
    // Constructors.
    // ------------------------------------------------------------------------
  
    /**
       Default constructor for SecureRandom. It constructs a 
       new SecureRandom by instantating the first SecureRandom 
       algorithm in the default security provier. 
  
       It is not seeded and should be seeded using setSeed or else
       on the first call to getnextBytes it will force a seed.
  
       It is maintained for backwards compatibility and programs
       should use {@link #getInstance(java.lang.String)}.
     */
    public SecureRandom()
    {
      Provider[] p = Security.getProviders();
  
      //Format of Key: SecureRandom.algname
      String key;
  
      String classname = null;
      int i;
      Enumeration e;
      for (i = 0; i < p.length; i++)
        {
          e = p[i].propertyNames();
          while (e.hasMoreElements())
            {
              key = (String) e.nextElement();
              if (key.startsWith("SECURERANDOM."))
                {
                  if ((classname = p[i].getProperty(key)) != null)
                    {
                      try
                        {
                          secureRandomSpi = (SecureRandomSpi) Class.
                            forName(classname).newInstance();
                          provider = p[i];
                          return;
                        }
                      catch (Throwable t)
  		      {
  			// Ignore.
  		      }
                    }
                }
            }
        }
  
      // Nothing found. Fall back to SHA1PRNG
      secureRandomSpi = new gnu.java.security.provider.SHA1PRNG();
    }
  
    /**
       A constructor for SecureRandom. It constructs a new 
       SecureRandom by instantating the first SecureRandom algorithm 
       in the default security provier. 
  
       It is seeded with the passed function and is useful if the user
       has access to hardware random device (like a radiation detector).
  
       It is maintained for backwards compatibility and programs
       should use getInstance.
  
       @param seed Seed bytes for class
     */
    public SecureRandom(byte[] seed)
    {
      this();
      setSeed(seed);
    }
  
    /**
       A constructor for SecureRandom. It constructs a new 
       SecureRandom using the specified SecureRandomSpi from
       the specified security provier. 
  
       @param secureRandomSpi A SecureRandomSpi class
       @param provider A Provider class
     */
    protected SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider)
    {
      this.secureRandomSpi = secureRandomSpi;
      this.provider = provider;
    }
  
    // Class methods.
    // ------------------------------------------------------------------------
  
    /**
     * Returns an instance of a SecureRandom. It creates the class from
     * the first provider that implements it.
     *
     * @param algorithm The algorithm name.
     * @return A new SecureRandom implementing the given algorithm.
     * @throws NoSuchAlgorithmException If no installed provider implements
     *         the given algorithm.
     */
    public static SecureRandom getInstance(String algorithm)
      throws NoSuchAlgorithmException
    {
      Provider[] p = Security.getProviders();
      
      for (int i = 0; i < p.length; i++)
        {
          try
            {
              return getInstance(algorithm, p[i]);
            }
          catch (NoSuchAlgorithmException e)
            {
  	    // Ignore.
            }
        }
  
      // None found.
      throw new NoSuchAlgorithmException(algorithm);
    }
  
    /**
     * Returns an instance of a SecureRandom. It creates the class
     * for the specified algorithm from the named provider.
     *
     * @param algorithm The algorithm name.
     * @param provider  The provider name.
     * @return A new SecureRandom implementing the chosen algorithm.
     * @throws NoSuchAlgorithmException If the named provider does not implement
     *         the algorithm, or if the implementation cannot be
     *         instantiated.
     * @throws NoSuchProviderException If no provider named
     *         <code>provider</code> is currently installed.
     * @throws IllegalArgumentException If <code>provider</code> is null
     *         or is empty.
     */
    public static SecureRandom getInstance(String algorithm, String provider)
    throws NoSuchAlgorithmException, NoSuchProviderException
    {
      if (provider == null || provider.length() == 0)
        throw new IllegalArgumentException("Illegal provider");
  
      Provider p = Security.getProvider(provider);
      if (p == null)
        throw new NoSuchProviderException();
      
      return getInstance(algorithm, p);
    }
  
    /**
     * Returns an instance of a SecureRandom. It creates the class for
     * the specified algorithm from the given provider.
     *
     * @param algorithm The SecureRandom algorithm to create.
     * @param provider  The provider to get the instance from.
     * @throws NoSuchAlgorithmException If the algorithm cannot be found, or
     *         if the class cannot be instantiated.
     * @throws IllegalArgumentException If <code>provider</code> is null.
     */
    public static SecureRandom getInstance(String algorithm, Provider provider)
    throws NoSuchAlgorithmException
    {
      if (provider == null)
        throw new IllegalArgumentException("Illegal provider");
      try
        {
          return new SecureRandom((SecureRandomSpi)
            Engine.getInstance(SECURE_RANDOM, algorithm, provider),
            provider);
        }
      catch (java.lang.reflect.InvocationTargetException ite)
        {
  	throw new NoSuchAlgorithmException(algorithm);
        }
      catch (ClassCastException cce)
        {
          throw new NoSuchAlgorithmException(algorithm);
        }
    }
  
    // Instance methods.
    // ------------------------------------------------------------------------
  
    /**
       Returns the provider being used by the current SecureRandom class.
  
       @return The provider from which this SecureRandom was attained
     */
    public final Provider getProvider()
    {
      return provider;
    }
  
    /**
       Seeds the SecureRandom. The class is re-seeded for each call and 
       each seed builds on the previous seed so as not to weaken security.
  
       @param seed seed bytes to seed with
     */
    public void setSeed(byte[] seed)
    {
      secureRandomSpi.engineSetSeed(seed);
    }
  
    /**
       Seeds the SecureRandom. The class is re-seeded for each call and 
       each seed builds on the previous seed so as not to weaken security.
  
       @param seed 8 seed bytes to seed with
     */
    public void setSeed(long seed)
    {
      // This particular setSeed will be called by Random.Random(), via
      // our own constructor, before secureRandomSpi is initialized.  In
      // this case we can't call a method on secureRandomSpi, and we
      // definitely don't want to throw a NullPointerException.
      // Therefore we test.
      if (secureRandomSpi != null)
        {
          byte[] tmp = { (byte) (0xff & (seed >> 56)),
  		       (byte) (0xff & (seed >> 48)),
  		       (byte) (0xff & (seed >> 40)),
  		       (byte) (0xff & (seed >> 32)),
  		       (byte) (0xff & (seed >> 24)),
  		       (byte) (0xff & (seed >> 16)),
  		       (byte) (0xff & (seed >> 8)),
  		       (byte) (0xff & seed)
          };
          secureRandomSpi.engineSetSeed(tmp);
        }
    }
  
    /**
       Generates a user specified number of bytes. This function
       is the basis for all the random functions.
  
       @param bytes array to store generated bytes in
     */
    public void nextBytes(byte[] bytes)
    {
      randomBytesUsed += bytes.length;
      counter++;
      secureRandomSpi.engineNextBytes(bytes);
    }
  
    /**
       Generates an integer containing the user specified
       number of random bits. It is right justified and padded
       with zeros.
  
       @param numBits number of random bits to get, 0 <= numBits <= 32;
  
       @return the random bits
     */
    protected final int next(int numBits)
    {
  