pqc/external/flint-2.4.3/fmpz_poly/interpolate_fmpz_vec.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
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) 2011 Fredrik Johansson
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_poly.h"
static void
_fmpz_poly_interpolate_newton(fmpz * ys, const fmpz * xs, slong n)
{
fmpz_t p, q, t;
slong i, j;
fmpz_init(p);
fmpz_init(q);
fmpz_init(t);
for (i = 1; i < n; i++)
{
fmpz_set(t, ys + i - 1);
for (j = i; j < n; j++)
{
fmpz_sub(p, ys + j, t);
fmpz_sub(q, xs + j, xs + j - i);
fmpz_set(t, ys + j);
fmpz_divexact(ys + j, p, q);
}
}
fmpz_clear(p);
fmpz_clear(q);
fmpz_clear(t);
}
void
fmpz_poly_interpolate_fmpz_vec(fmpz_poly_t poly,
const fmpz * xs, const fmpz * ys, slong n)
{
if (n == 0)
{
fmpz_poly_zero(poly);
return;
}
else if (n == 1)
{
fmpz_poly_set_fmpz(poly, ys);
return;
}
else
{
fmpz_poly_fit_length(poly, n);
_fmpz_vec_set(poly->coeffs, ys, n);
_fmpz_poly_interpolate_newton(poly->coeffs, xs, n);
_fmpz_poly_set_length(poly, n);
_fmpz_poly_normalise(poly);
_fmpz_poly_newton_to_monomial(poly->coeffs, xs, poly->length);
}
}