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

182 lines
5.0 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
Copyright (C) 2012 Lina Kulakova
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "fmpz_vec.h"
#include "fmpz_mod_poly.h"
#include "fmpz_mat.h"
#include "ulong_extras.h"
void
_fmpz_mod_poly_compose_mod_brent_kung(fmpz * res, const fmpz * poly1, slong len1,
const fmpz * poly2, const fmpz * poly3, slong len3,
const fmpz_t p)
{
fmpz_mat_t A, B, C;
fmpz * t, * h, * tmp;
slong i, j, n, m;
n = len3 - 1;
if (len3 == 1)
return;
if (len1 == 1)
{
fmpz_set(res, poly1);
return;
}
if (len3 == 2)
{
_fmpz_mod_poly_evaluate_fmpz(res, poly1, len1, poly2, p);
return;
}
m = n_sqrt(n) + 1;
fmpz_mat_init(A, m, n);
fmpz_mat_init(B, m, m);
fmpz_mat_init(C, m, n);
h = _fmpz_vec_init(2 * n - 1);
t = _fmpz_vec_init(2 * n - 1);
/* Set rows of B to the segments of poly1 */
for (i = 0; i < len1 / m; i++)
_fmpz_vec_set(B->rows[i], poly1 + i * m, m);
_fmpz_vec_set(B->rows[i], poly1 + i * m, len1 % m);
/* Set rows of A to powers of poly2 */
fmpz_one(A->rows[0]);
_fmpz_vec_set(A->rows[1], poly2, n);
tmp = _fmpz_vec_init(2 * n - 1);
for (i = 2; i < m; i++)
{
_fmpz_mod_poly_mulmod(tmp, A->rows[i - 1], n, poly2, n, poly3, len3, p);
_fmpz_vec_set(A->rows[i], tmp, n);
}
_fmpz_vec_clear(tmp, 2 * n - 1);
fmpz_mat_mul(C, B, A);
for (i = 0; i < m; i++)
for (j = 0; j < n; j++)
fmpz_mod(C->rows[i] + j, C->rows[i] + j, p);
/* Evaluate block composition using the Horner scheme */
_fmpz_vec_set(res, C->rows[m - 1], n);
_fmpz_mod_poly_mulmod(h, A->rows[m - 1], n, poly2, n, poly3, len3, p);
for (i = m - 2; i >= 0; i--)
{
_fmpz_mod_poly_mulmod(t, res, n, h, n, poly3, len3, p);
_fmpz_mod_poly_add(res, t, n, C->rows[i], n, p);
}
_fmpz_vec_clear(h, 2 * n - 1);
_fmpz_vec_clear(t, 2 * n - 1);
fmpz_mat_clear(A);
fmpz_mat_clear(B);
fmpz_mat_clear(C);
}
void
fmpz_mod_poly_compose_mod_brent_kung(fmpz_mod_poly_t res, const fmpz_mod_poly_t poly1,
const fmpz_mod_poly_t poly2, const fmpz_mod_poly_t poly3)
{
slong len1 = poly1->length;
slong len2 = poly2->length;
slong len3 = poly3->length;
slong len = len3 - 1;
slong vec_len = FLINT_MAX(len3 - 1, len2);
fmpz * ptr2;
fmpz_t inv3;
if (len3 == 0)
{
flint_printf("Exception (fmpz_mod_poly_compose_mod_brent_kung)."
"Division by zero in\n");
abort();
}
if (len1 >= len3)
{
flint_printf("Exception (fmpz_mod_poly_compose_brent_kung). the degree of the"
" first polynomial must be smaller than that of the modulus\n");
abort();
}
if (len1 == 0 || len3 == 1)
{
fmpz_mod_poly_zero(res);
return;
}
if (len1 == 1)
{
fmpz_mod_poly_set(res, poly1);
return;
}
if (res == poly3 || res == poly1)
{
fmpz_mod_poly_t tmp;
fmpz_mod_poly_init(tmp, &res->p);
fmpz_mod_poly_compose_mod_brent_kung(tmp, poly1, poly2, poly3);
fmpz_mod_poly_swap(tmp, res);
fmpz_mod_poly_clear(tmp);
return;
}
ptr2 = _fmpz_vec_init(vec_len);
if (len2 <= len)
{
_fmpz_vec_set(ptr2, poly2->coeffs, len2);
_fmpz_vec_zero(ptr2 + len2, vec_len - len2);
}
else
{
fmpz_init(inv3);
fmpz_invmod(inv3, poly3->coeffs + len, &res->p);
_fmpz_mod_poly_rem(ptr2, poly2->coeffs, len2,
poly3->coeffs, len3, inv3, &res->p);
fmpz_clear(inv3);
}
fmpz_mod_poly_fit_length(res, len);
_fmpz_mod_poly_compose_mod_brent_kung(res->coeffs,
poly1->coeffs, len1, ptr2, poly3->coeffs, len3, &res->p);
_fmpz_mod_poly_set_length(res, len);
_fmpz_mod_poly_normalise(res);
_fmpz_vec_clear(ptr2, vec_len);
}