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

169 lines
4.4 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_mod_brent_kung(mp_ptr res, mp_srcptr poly1, slong len1,
mp_srcptr poly2,
mp_srcptr poly3, slong len3, nmod_t mod)
{
nmod_mat_t A, B, C;
mp_ptr t, h;
slong i, n, m;
n = len3 - 1;
if (len3 == 1)
return;
if (len1 == 1)
{
res[0] = poly1[0];
return;
}
if (len3 == 2)
{
res[0] = _nmod_poly_evaluate_nmod(poly1, len1, poly2[0], mod);
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, n);
for (i = 2; i < m; i++)
_nmod_poly_mulmod(A->rows[i], A->rows[i-1],
n, poly2, n, poly3, len3, 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_mulmod(h, A->rows[m - 1], n, poly2, n, poly3, len3, mod);
for (i = m - 2; i >= 0; i--)
{
_nmod_poly_mulmod(t, res, n, h, n, poly3, len3, 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_mod_brent_kung(nmod_poly_t res,
const nmod_poly_t poly1, const nmod_poly_t poly2,
const nmod_poly_t poly3)
{
slong len1 = poly1->length;
slong len2 = poly2->length;
slong len3 = poly3->length;
slong len = len3 - 1;
mp_ptr ptr2;
if (len3 == 0)
{
flint_printf("Exception (nmod_poly_compose_mod_brent_kung). Division by zero.\n");
abort();
}
if (len1 >= len3)
{
flint_printf("Exception (nmod_poly_compose_brent_kung). The degree of the \n"
"first polynomial must be smaller than that of the modulus.\n");
abort();
}
if (len1 == 0 || len3 == 1)
{
nmod_poly_zero(res);
return;
}
if (len1 == 1)
{
nmod_poly_set(res, poly1);
return;
}
if (res == poly3 || res == poly1)
{
nmod_poly_t tmp;
nmod_poly_init_preinv(tmp, res->mod.n, res->mod.ninv);
nmod_poly_compose_mod_brent_kung(tmp, poly1, poly2, poly3);
nmod_poly_swap(tmp, res);
nmod_poly_clear(tmp);
return;
}
ptr2 = _nmod_vec_init(len);
if (len2 <= len)
{
flint_mpn_copyi(ptr2, poly2->coeffs, len2);
flint_mpn_zero(ptr2 + len2, len - len2);
}
else
{
_nmod_poly_rem(ptr2, poly2->coeffs, len2,
poly3->coeffs, len3, res->mod);
}
nmod_poly_fit_length(res, len);
_nmod_poly_compose_mod_brent_kung(res->coeffs,
poly1->coeffs, len1, ptr2, poly3->coeffs, len3, res->mod);
res->length = len;
_nmod_poly_normalise(res);
_nmod_vec_clear(ptr2);
}