pqc/external/flint-2.4.3/nmod_poly/inv_series_newton.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
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
Copyright (C) 2011 Fredrik Johansson
Copyright (C) 2011 Sebastian Pancratz
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
#include "ulong_extras.h"
#define NMOD_POLY_INV_NEWTON_CUTOFF 400
void
_nmod_poly_inv_series_newton(mp_ptr Qinv, mp_srcptr Q, slong n, nmod_t mod)
{
if (n < NMOD_POLY_INV_NEWTON_CUTOFF)
{
_nmod_poly_inv_series_basecase(Qinv, Q, n, mod);
}
else
{
slong *a, i, m;
mp_ptr W;
for (i = 1; (WORD(1) << i) < n; i++) ;
W = flint_malloc(n * sizeof(mp_limb_t) + i * sizeof(slong));
a = (slong *) (W + n);
a[i = 0] = n;
while (n >= NMOD_POLY_INV_NEWTON_CUTOFF)
a[++i] = (n = (n + 1) / 2);
_nmod_poly_inv_series_basecase(Qinv, Q, n, mod);
for (i--; i >= 0; i--)
{
m = n;
n = a[i];
_nmod_poly_mullow(W, Q, n, Qinv, m, n, mod);
_nmod_poly_mullow(Qinv + m, Qinv, m, W + m, n - m, n - m, mod);
_nmod_vec_neg(Qinv + m, Qinv + m, n - m, mod);
}
flint_free(W);
}
}
void
nmod_poly_inv_series_newton(nmod_poly_t Qinv, const nmod_poly_t Q, slong n)
{
const slong Qlen = Q->length;
mp_ptr q, qinv;
if (n == 0 || Q->length == 0 || Q->coeffs[0] == 0)
{
flint_printf("Exception (nmod_poly_inv_series_newton). Division by zero.\n");
abort();
}
if (Qlen < n)
{
q = _nmod_vec_init(n);
flint_mpn_copyi(q, Q->coeffs, Qlen);
flint_mpn_zero(q + Qlen, n - Qlen);
}
else
{
q = Q->coeffs;
}
if (Q == Qinv && Qlen >= n)
{
qinv = _nmod_vec_init(n);
}
else
{
nmod_poly_fit_length(Qinv, n);
qinv = Qinv->coeffs;
}
_nmod_poly_inv_series_newton(qinv, q, n, Q->mod);
if (Q == Qinv && Qlen >= n)
{
flint_free(Qinv->coeffs);
Qinv->coeffs = qinv;
Qinv->alloc = n;
Qinv->length = n;
}
else
{
Qinv->length = n;
}
if (Qlen < n)
{
_nmod_vec_clear(q);
}
_nmod_poly_normalise(Qinv);
}