source: trunk/linbox/linbox/randiter/random-fftprime.h @ 4085

/* -*- mode: C++; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*- */
// vim:sts=8:sw=8:ts=8:noet:sr:cino=>s,f0,{0,g0,(0,\:0,t0,+0,=s
/* linbox/algorithms/
 * Copyright (C) 2005  Pascal Giorgi
 *
 * Written by Pascal Giorgi <pgiorgi@uwaterloo.ca>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */


#ifndef __LINBOX_random_fftprime_H
#define __LINBOX_random_fftprime_H

#include "linbox/integer.h"
#include "linbox/util/timer.h"

namespace LinBox
{

        class RandomFFTPrime {
        public:

                int         _bits;

                RandomFFTPrime(int bits = 20, unsigned long seed = 0) :
                        _bits(bits)
                {
                        if (! seed)
                                RandomFFTPrime::setSeed( (unsigned long)BaseTimer::seed() );
                        else
                                RandomFFTPrime::setSeed( seed );
                }

                // define the prime type
                typedef integer Prime_Type;

                /** @brief randomPrime()
                 *  return a random prime
                 */
                inline Prime_Type randomPrime() const
                {
                        integer tmp;
                        size_t cbits=5;
                        size_t tresh;
                        do {
                                tresh = 1<<(cbits);
                                size_t p = 1<<((size_t)_bits-cbits);
                                do {
                                        integer::random(tmp,cbits);
                                        tmp = tmp*p+1;
                                        tresh--;
                                } while (( Givaro::probab_prime(tmp)<2) && (tresh));
                                cbits++;
                        }
                        while(tresh==0);
                        return tmp;
                }

                /** @brief randomPrime(Prime_Type& p)
                 *  return a random prime
                 */
                inline Prime_Type randomPrime (Prime_Type& t) const
                {
                        size_t cbits=5;
                        size_t tresh;
                        do {
                                tresh = 1<<(cbits);
                                size_t p = 1<<((size_t)_bits-cbits);
                                do {
                                        integer::random(t,cbits);
                                        t = t*p+1;
                                        tresh--;
                                } while (!Givaro::probab_prime(t) && (tresh));
                                cbits++;
                        }
                        while(tresh==0);

                        return t;
                }

                /** @brief setSeed (unsigned long ul)
                 *  Set the random seed to be ul.
                 */
                void static setSeed(unsigned long ul)
                {
                        integer::seeding(ul);
                }


        };
}

#endif //__LINBOX_random_fftprime_H