using_infrastructure.c++

This example illustrates how to use the FAAST::Field::switchContext(), FAAST::FieldElement::toInfrastructure(), FAAST::FieldPolynomial::toInfrastructure() and FAAST::Field::fromInfrastructure() methods.

Warning

This is for advanced use only, you shouldn't care about this on an ordinary use of the library.

/*
    This file is part of the FAAST library.

    Copyright (c) 2009 Luca De Feo and Éric Schost.

    The most recent version of FAAST is available at http://www.lix.polytechnique.fr/~defeo/FAAST

    This program 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.

    This program 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 this program; see file COPYING. If not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
*/
#include <faast.hpp>
using namespace FAAST;
void main() {
    Field<zz_p_algebra>& K = Field<zz_p_Algebra>::createField(2, 3);
    Field<zz_p_algebra>& L = K.ArtinSchreierExtension();

    /* Set the context to work in K. */
    K.switchContext();
    NTL::zz_pX a_polynomial, another_polynomial;

    /* Do something with a_polynomial and another_polynomial
     * WARNING ! If you make library calls here, do not forget
     * to set the context back with K.switchContext().
     */
    ...

    /* Convert a_polynomial to an element of K. */
    NTL::zz_pE an_element = NTL::to_zz_pE(a_polynomial);
    FieldElement<zz_p_Algebra> a = K.fromInfrastructure(an_element);

    /* Convert another_polynomial to an element of L. This makes sense since
     * K and L have the same characteristic.
     */
    L.switchContext();
    NTL::zz_pE another_element = NTL::to_zz_pE(another_polynomial);
    FieldElement<zz_p_Algebra> b = L.fromInfrastructure(another_element);

    /* Now work using the library. You don't have to worry about
     * switching the context as the library does it for you.
     */
    FieldElement<zz_p_Algebra> c = a >> L;
    c *= b;

    /* Extract the NTL representation out of c */
    NTL::zz_pE yet_another_element;
    c.toInfrastructure(yet_another_element);

    /* We call an \NTL function not available in the library
     * and we convert the result back to a FieldElement
     */
    L.switchContext();  // this is optional because toInfrastructure()
                        // already switched the context.
    NTL:zz_pX yet_another_polynomial = NTL::rep(yet_another_element);
    NTL::LeftShift(yet_another_polynomial, yet_another_polynomial, 1);
    yet_another_element = NTL::to_zz_pE(yet_another_polynomial);
    c = L.fromInfrastructure(yet_another_element);
}