Subversion Repositories openrisc

/* Prime.java --- Prime number generation utilities

   Copyright (C) 1999, 2004 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., 51 Franklin Street, 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.util;

import java.math.BigInteger;

import java.util.Random;

//import java.security.SecureRandom;

public final class Prime

{

  /*

    See IEEE P1363 A.15.4 (10/05/98 Draft)

  */

  public static BigInteger generateRandomPrime( int pmin, int pmax, BigInteger f )

  {

    BigInteger d;

    //Step 1 - generate prime

    BigInteger p = new BigInteger( (pmax + pmin)/2, new Random() );

    if( p.compareTo( BigInteger.valueOf( 1 ).shiftLeft( pmin ) ) <= 0 )

      {

        p = p.add( BigInteger.valueOf( 1 ).shiftLeft( pmin ).subtract( p ) );

      }

    //Step 2 - test for even

    if( p.mod( BigInteger.valueOf(2) ).compareTo( BigInteger.valueOf( 0 )) == 0)

      p = p.add( BigInteger.valueOf( 1 ) );

    for(;;)

      {

        //Step 3

        if( p.compareTo( BigInteger.valueOf( 1 ).shiftLeft( pmax)) > 0)

          {

            //Step 3.1

            p = p.subtract( BigInteger.valueOf( 1 ).shiftLeft( pmax) );

            p = p.add( BigInteger.valueOf( 1 ).shiftLeft( pmin) );

            p = p.subtract( BigInteger.valueOf( 1 ) );

            //Step 3.2

            // put step 2 code here so looping code is cleaner

            //Step 2 - test for even

            if( p.mod( BigInteger.valueOf(2) ).compareTo( BigInteger.valueOf( 0 )) == 0)

              p = p.add( BigInteger.valueOf( 1 ) );

            continue;

          }

        //Step 4 - compute GCD

        d = p.subtract( BigInteger.valueOf(1) );

        d = d.gcd( f );

        //Step 5 - test d

        if( d.compareTo( BigInteger.valueOf( 1 ) ) == 0)

          {

            //Step 5.1 - test primality

            if( p.isProbablePrime( 1 ) == true )

              {

                                //Step 5.2;

                return p;

              }

          }

        //Step 6

        p = p.add( BigInteger.valueOf( 2 ) );

        //Step 7

      }

  }

  /*

    See IEEE P1363 A.15.5 (10/05/98 Draft)

  */

  public static BigInteger generateRandomPrime( BigInteger r, BigInteger a, int pmin, int pmax, BigInteger f )

  {

    BigInteger d, w;

    //Step 1 - generate prime

    BigInteger p = new BigInteger( (pmax + pmin)/2, new Random() );

  steptwo:{ //Step 2

      w = p.mod( r.multiply( BigInteger.valueOf(2) ));

      //Step 3

      p = p.add( r.multiply( BigInteger.valueOf(2) ) );

      p = p.subtract( w );

      p = p.add(a);

      //Step 4 - test for even

      if( p.mod( BigInteger.valueOf(2) ).compareTo( BigInteger.valueOf( 0 )) == 0)

        p = p.add( r );

      for(;;)

        {

          //Step 5

          if( p.compareTo( BigInteger.valueOf( 1 ).shiftLeft( pmax)) > 0)

            {

              //Step 5.1

              p = p.subtract( BigInteger.valueOf( 1 ).shiftLeft( pmax) );

              p = p.add( BigInteger.valueOf( 1 ).shiftLeft( pmin) );

              p = p.subtract( BigInteger.valueOf( 1 ) );

              //Step 5.2 - goto to Step 2

              break steptwo;

            }

          //Step 6

          d = p.subtract( BigInteger.valueOf(1) );

          d = d.gcd( f );

          //Step 7 - test d

          if( d.compareTo( BigInteger.valueOf( 1 ) ) == 0)

            {

              //Step 7.1 - test primality

              if( p.isProbablePrime( 1 ) == true )

                {

                                //Step 7.2;

                  return p;

                }

            }

          //Step 8

          p = p.add( r.multiply( BigInteger.valueOf(2) ) );

          //Step 9

        }

    }

    //Should never reach here but makes the compiler happy

    return BigInteger.valueOf(0);

  }

}