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

123 lines
3.6 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 William Hart
Copyright (C) 2012 Sebastian Pancratz
******************************************************************************/
#include "nmod_poly.h"
#include "ulong_extras.h"
void
_nmod_poly_compose_horner(mp_ptr res, mp_srcptr poly1, slong len1,
mp_srcptr poly2, slong len2, nmod_t mod)
{
if (len1 == 1)
{
res[0] = poly1[0];
}
else if (len2 == 1)
{
res[0] = _nmod_poly_evaluate_nmod(poly1, len1, poly2[0], mod);
}
else if (len1 == 2)
{
_nmod_vec_scalar_mul_nmod(res, poly2, len2, poly1[1], mod);
res[0] = n_addmod(res[0], poly1[0], mod.n);
}
else
{
const slong alloc = (len1 - 1) * (len2 - 1) + 1;
slong i = len1 - 1, lenr = len2;
mp_limb_t *t, *t1, *t2;
t = _nmod_vec_init(alloc);
if (len1 % 2 == 0)
{
t1 = res;
t2 = t;
}
else
{
t1 = t;
t2 = res;
}
/* Perform the first two steps as one,
"res = a(m) * poly2 + a(m-1)". */
{
_nmod_vec_scalar_mul_nmod(t1, poly2, len2, poly1[i], mod);
i--;
t1[0] = n_addmod(t1[0], poly1[i], mod.n);
}
while (i--)
{
_nmod_poly_mul(t2, t1, lenr, poly2, len2, mod);
lenr += len2 - 1;
MP_PTR_SWAP(t1, t2);
t1[0] = n_addmod(t1[0], poly1[i], mod.n);
}
_nmod_vec_clear(t);
}
}
void nmod_poly_compose_horner(nmod_poly_t res,
const nmod_poly_t poly1, const nmod_poly_t poly2)
{
const slong len1 = poly1->length;
const slong len2 = poly2->length;
if (len1 == 0)
{
nmod_poly_zero(res);
}
else if (len1 == 1 || len2 == 0)
{
nmod_poly_fit_length(res, 1);
res->coeffs[0] = poly1->coeffs[0];
res->length = (res->coeffs[0] != 0);
}
else
{
const slong lenr = (len1 - 1) * (len2 - 1) + 1;
if (res != poly1 && res != poly2)
{
nmod_poly_fit_length(res, lenr);
_nmod_poly_compose_horner(res->coeffs, poly1->coeffs, len1,
poly2->coeffs, len2, poly1->mod);
}
else
{
nmod_poly_t t;
nmod_poly_init2(t, poly1->mod.n, lenr);
_nmod_poly_compose_horner(t->coeffs, poly1->coeffs, len1,
poly2->coeffs, len2, poly1->mod);
nmod_poly_swap(res, t);
nmod_poly_clear(t);
}
res->length = lenr;
_nmod_poly_normalise(res);
}
}