pqc/external/flint-2.4.3/nmod_poly/compose_series_horner.c
2014-05-24 23:16:06 +02:00

128 lines
3.7 KiB
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) 2010 Sebastian Pancratz
Copyright (C) 2011 Fredrik Johansson
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
#include "ulong_extras.h"
void
_nmod_poly_compose_series_horner(mp_ptr res, mp_srcptr poly1, slong len1,
mp_srcptr poly2, slong len2, slong n, nmod_t mod)
{
if (n == 1)
{
res[0] = poly1[0];
}
else
{
slong i = len1 - 1;
slong lenr;
mp_ptr t = _nmod_vec_init(n);
lenr = len2;
_nmod_vec_scalar_mul_nmod(res, poly2, len2, poly1[i], mod);
i--;
res[0] = nmod_add(res[0], poly1[i], mod);
while (i > 0)
{
i--;
if (lenr + len2 - 1 < n)
{
_nmod_poly_mul(t, res, lenr, poly2, len2, mod);
lenr = lenr + len2 - 1;
}
else
{
_nmod_poly_mullow(t, res, lenr, poly2, len2, n, mod);
lenr = n;
}
_nmod_poly_add(res, t, lenr, poly1 + i, 1, mod);
}
_nmod_vec_zero(res + lenr, n - lenr);
_nmod_vec_clear(t);
}
}
void
nmod_poly_compose_series_horner(nmod_poly_t res,
const nmod_poly_t poly1, const nmod_poly_t poly2, slong n)
{
slong len1 = poly1->length;
slong len2 = poly2->length;
slong lenr;
if (len2 != 0 && poly2->coeffs[0] != 0)
{
flint_printf("Exception (nmod_poly_compose_series_horner). Inner polynomial "
"must have zero constant term.\n");
abort();
}
if (len1 == 0 || n == 0)
{
nmod_poly_zero(res);
return;
}
if (len2 == 0 || len1 == 1)
{
nmod_poly_fit_length(res, 1);
res->coeffs[0] = poly1->coeffs[0];
res->length = 1;
_nmod_poly_normalise(res);
return;
}
lenr = FLINT_MIN((len1 - 1) * (len2 - 1) + 1, n);
len1 = FLINT_MIN(len1, lenr);
len2 = FLINT_MIN(len2, lenr);
if ((res != poly1) && (res != poly2))
{
nmod_poly_fit_length(res, lenr);
_nmod_poly_compose_series_horner(res->coeffs, poly1->coeffs, len1,
poly2->coeffs, len2, lenr, res->mod);
res->length = lenr;
_nmod_poly_normalise(res);
}
else
{
nmod_poly_t t;
nmod_poly_init2_preinv(t, res->mod.n, res->mod.ninv, lenr);
_nmod_poly_compose_series_horner(t->coeffs, poly1->coeffs, len1,
poly2->coeffs, len2, lenr, res->mod);
t->length = lenr;
_nmod_poly_normalise(t);
nmod_poly_swap(res, t);
nmod_poly_clear(t);
}
}