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

141 lines
4.0 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) 2011 Fredrik Johansson
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
#include "nmod_mat.h"
#include "ulong_extras.h"
void
_nmod_poly_compose_series_brent_kung(mp_ptr res, mp_srcptr poly1, slong len1,
mp_srcptr poly2, slong len2, slong n, nmod_t mod)
{
nmod_mat_t A, B, C;
mp_ptr t, h;
slong i, m;
if (n == 1)
{
res[0] = poly1[0];
return;
}
m = n_sqrt(n) + 1;
nmod_mat_init(A, m, n, mod.n);
nmod_mat_init(B, m, m, mod.n);
nmod_mat_init(C, m, n, mod.n);
h = _nmod_vec_init(n);
t = _nmod_vec_init(n);
/* Set rows of B to the segments of poly1 */
for (i = 0; i < len1 / m; i++)
_nmod_vec_set(B->rows[i], poly1 + i*m, m);
_nmod_vec_set(B->rows[i], poly1 + i*m, len1 % m);
/* Set rows of A to powers of poly2 */
A->rows[0][0] = UWORD(1);
_nmod_vec_set(A->rows[1], poly2, len2);
for (i = 2; i < m; i++)
_nmod_poly_mullow(A->rows[i], A->rows[i-1], n, poly2, len2, n, mod);
nmod_mat_mul(C, B, A);
/* Evaluate block composition using the Horner scheme */
_nmod_vec_set(res, C->rows[m - 1], n);
_nmod_poly_mullow(h, A->rows[m - 1], n, poly2, len2, n, mod);
for (i = m - 2; i >= 0; i--)
{
_nmod_poly_mullow(t, res, n, h, n, n, mod);
_nmod_poly_add(res, t, n, C->rows[i], n, mod);
}
_nmod_vec_clear(h);
_nmod_vec_clear(t);
nmod_mat_clear(A);
nmod_mat_clear(B);
nmod_mat_clear(C);
}
void
nmod_poly_compose_series_brent_kung(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_brent_kung). Inner \n"
"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_brent_kung(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_brent_kung(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);
}
}