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

106 lines
2.7 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) 2011 William Hart
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
#include "ulong_extras.h"
void
_nmod_poly_inv_series_basecase(mp_ptr Qinv,
mp_srcptr Q, slong n, nmod_t mod)
{
mp_ptr X2n, Qrev;
X2n = _nmod_vec_init(2*n);
Qrev = X2n + n;
_nmod_poly_reverse(Qrev, Q, n, n);
X2n[n - 1] = 1;
flint_mpn_zero(X2n, n - 1);
X2n -= (n - 1);
_nmod_poly_div_divconquer(Qinv, X2n, 2*n - 1, Qrev, n, mod);
_nmod_poly_reverse(Qinv, Qinv, n, n);
_nmod_vec_clear(X2n + n - 1);
}
void
nmod_poly_inv_series_basecase(nmod_poly_t Qinv,
const nmod_poly_t Q, slong n)
{
mp_ptr Qinv_coeffs, Q_coeffs;
nmod_poly_t t1;
slong Qlen;
Qlen = Q->length;
if (n == 0 || Q->length == 0 || Q->coeffs[0] == 0)
{
flint_printf("Exception (nmod_poly_inv_series_basecase). Division by zero.\n");
abort();
}
if (Qlen < n)
{
Q_coeffs = _nmod_vec_init(n);
flint_mpn_copyi(Q_coeffs, Q->coeffs, Qlen);
flint_mpn_zero(Q_coeffs + Qlen, n - Qlen);
}
else
Q_coeffs = Q->coeffs;
if (Q == Qinv && Qlen >= n)
{
nmod_poly_init2(t1, Q->mod.n, n);
Qinv_coeffs = t1->coeffs;
}
else
{
nmod_poly_fit_length(Qinv, n);
Qinv_coeffs = Qinv->coeffs;
}
_nmod_poly_inv_series_basecase(Qinv_coeffs, Q_coeffs, n, Q->mod);
if (Q == Qinv && Qlen >= n)
{
nmod_poly_swap(Qinv, t1);
nmod_poly_clear(t1);
}
Qinv->length = n;
if (Qlen < n)
_nmod_vec_clear(Q_coeffs);
_nmod_poly_normalise(Qinv);
}