arb/acb_dft/dft_pol.c

/*
    Copyright (C) 2016 Pascal Molin

    This file is part of Arb.

    Arb is free software: you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 2.1 of the License, or
    (at your option) any later version.  See <http://www.gnu.org/licenses/>.
*/

#include "acb_poly.h"
#include "acb_dft.h"

/* all roots are already computed */
void
_acb_dft_pol(acb_ptr w, acb_srcptr v, slong dv, acb_srcptr z, slong dz, slong len, slong prec)
{
    slong i, j;
    acb_ptr wi;
    acb_srcptr vj;

    for (i = 0, wi = w; i < len; i++, wi++)
    {
        acb_zero(wi);
        for (j = 0, vj = v; j < len; j++, vj += dv)
            acb_addmul(wi, vj, z + dz * (i * j % len), prec);
    }
}

void
acb_dft_pol(acb_ptr w, acb_srcptr v, slong len, slong prec)
{
    acb_ptr z;
    z = _acb_vec_init(len);
    _acb_vec_unit_roots(z, len, prec);
    _acb_dft_pol(w, v, 1, z, 1, len, prec);
    _acb_vec_clear(z, len);
}

void
_acb_dft_pol_init(acb_dft_pol_t pol, slong dv, acb_ptr z, slong dz, slong len, slong prec)
{
    pol->n = len;
    pol->dv = dv;

    if (z == NULL)
    {
        if (DFT_VERB)
            flint_printf("warning: init z[%ld] in dft_pol, should be avoided\n",len);
        pol->z = _acb_vec_init(len);
        _acb_vec_unit_roots(pol->z, len, prec);
        pol->dz = 1;
        pol->zclear = 1;
    }
    else
    {
        pol->z = z;
        pol->dz = dz;
        pol->zclear = 0;
    }
}