pqc/external/flint-2.4.3/fq_poly_templates/powmod_ui_binexp.c

/*=============================================================================

    This file is part of FLINT.

    FLINT 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.

    FLINT 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 FLINT; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA

=============================================================================*/
/******************************************************************************

    Copyright (C) 2013 Mike Hansen

******************************************************************************/


#ifdef T

#include "templates.h"

#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "ulong_extras.h"
void
_TEMPLATE(T, poly_powmod_ui_binexp) (TEMPLATE(T, struct) * res,
                                     const TEMPLATE(T, struct) * poly, ulong e,
                                     const TEMPLATE(T, struct) * f, slong lenf,
                                     const TEMPLATE(T, ctx_t) ctx)
{
    TEMPLATE(T, struct) * T, *Q;
    TEMPLATE(T, t) invf;
    slong lenT, lenQ;
    int i;

    if (lenf == 2)
    {
        TEMPLATE(T, pow_ui) (res, poly, e, ctx);
        return;
    }

    lenT = 2 * lenf - 3;
    lenQ = FLINT_MAX(lenT - lenf + 1, 1);

    T = _TEMPLATE(T, vec_init) (lenT + lenQ, ctx);
    Q = T + lenT;

    TEMPLATE(T, init) (invf, ctx);
    TEMPLATE(T, inv) (invf, f + lenf - 1, ctx);

    _TEMPLATE(T, vec_set) (res, poly, lenf - 1, ctx);

    for (i = ((int)FLINT_BIT_COUNT(e) - 2); i >= 0; i--)
    {
        _TEMPLATE(T, poly_sqr) (T, res, lenf - 1, ctx);
        _TEMPLATE(T, poly_divrem) (Q, res, T, 2 * lenf - 3, f, lenf, invf,
                                   ctx);

        if (e & (UWORD(1) << i))
        {
            _TEMPLATE(T, poly_mul) (T, res, lenf - 1, poly, lenf - 1, ctx);
            _TEMPLATE(T, poly_divrem) (Q, res, T, 2 * lenf - 3, f, lenf, invf,
                                       ctx);
        }
    }

    TEMPLATE(T, clear) (invf, ctx);
    _TEMPLATE(T, vec_clear) (T, lenT + lenQ, ctx);
}


void
TEMPLATE(T, poly_powmod_ui_binexp) (TEMPLATE(T, poly_t) res,
                                    const TEMPLATE(T, poly_t) poly, ulong e,
                                    const TEMPLATE(T, poly_t) f,
                                    const TEMPLATE(T, ctx_t) ctx)
{
    TEMPLATE(T, struct) * q;
    slong len = poly->length;
    slong lenf = f->length;
    slong trunc = lenf - 1;
    int qcopy = 0;

    if (lenf == 0)
    {
        TEMPLATE_PRINTF
            ("Exception: %s_poly_powmod_ui_binexp: divide by zero\n", T);
        abort();
    }

    if (len >= lenf)
    {
        TEMPLATE(T, poly_t) t, r;
        TEMPLATE(T, poly_init) (t, ctx);
        TEMPLATE(T, poly_init) (r, ctx);
        TEMPLATE(T, poly_divrem) (t, r, poly, f, ctx);
        TEMPLATE(T, poly_powmod_ui_binexp) (res, r, e, f, ctx);
        TEMPLATE(T, poly_clear) (t, ctx);
        TEMPLATE(T, poly_clear) (r, ctx);
        return;
    }

    if (e <= 2)
    {
        if (e == UWORD(0))
        {
            TEMPLATE(T, poly_fit_length) (res, 1, ctx);
            TEMPLATE(T, one) (res->coeffs, ctx);
            _TEMPLATE(T, poly_set_length) (res, 1, ctx);
        }
        else if (e == UWORD(1))
        {
            TEMPLATE(T, poly_set) (res, poly, ctx);
        }
        else
            TEMPLATE(T, poly_mulmod) (res, poly, poly, f, ctx);
        return;
    }

    if (lenf == 1 || len == 0)
    {
        TEMPLATE(T, poly_zero) (res, ctx);
        return;
    }

    if (len < trunc)
    {
        q = _TEMPLATE(T, vec_init) (trunc, ctx);
        _TEMPLATE(T, vec_set) (q, poly->coeffs, len, ctx);
        _TEMPLATE(T, vec_zero) (q + len, trunc - len, ctx);
        qcopy = 1;
    }
    else
        q = poly->coeffs;

    if ((res == poly && !qcopy) || (res == f))
    {
        TEMPLATE(T, poly_t) t;
        TEMPLATE(T, poly_init2) (t, 2 * lenf - 3, ctx);
        _TEMPLATE(T, poly_powmod_ui_binexp) (t->coeffs, q, e, f->coeffs, lenf,
                                             ctx);
        TEMPLATE(T, poly_swap) (res, t, ctx);
        TEMPLATE(T, poly_clear) (t, ctx);
    }
    else
    {
        TEMPLATE(T, poly_fit_length) (res, 2 * lenf - 3, ctx);
        _TEMPLATE(T, poly_powmod_ui_binexp) (res->coeffs, q, e, f->coeffs,
                                             lenf, ctx);
    }

    if (qcopy)
        _TEMPLATE(T, vec_clear) (q, trunc, ctx);

    _TEMPLATE(T, poly_set_length) (res, trunc, ctx);
    _TEMPLATE(T, poly_normalise) (res, ctx);
}


#endif