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

135 lines
3.7 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) 2010, 2011 Sebastian Pancratz
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"
#include "fmpz_mod_poly.h"
#define FMPZ_MOD_POLY_INV_NEWTON_CUTOFF 64
void
_fmpz_mod_poly_inv_series_newton(fmpz * Qinv, const fmpz * Q, slong n,
const fmpz_t cinv, const fmpz_t p)
{
if (n == 1) /* {Q,1} * cinv == 1 mod (x) */
{
fmpz_set(Qinv, cinv);
}
else
{
const slong alloc = FLINT_MAX(n, 3 * FMPZ_MOD_POLY_INV_NEWTON_CUTOFF);
slong *a, i, m;
fmpz *W;
W = _fmpz_vec_init(alloc);
for (i = 1; (WORD(1) << i) < n; i++) ;
a = (slong *) flint_malloc(i * sizeof(slong));
a[i = 0] = n;
while (n >= FMPZ_MOD_POLY_INV_NEWTON_CUTOFF)
a[++i] = (n = (n + 1) / 2);
/* Base case */
{
fmpz *Qrev = W + 2 * FMPZ_MOD_POLY_INV_NEWTON_CUTOFF;
_fmpz_poly_reverse(Qrev, Q, n, n);
_fmpz_vec_zero(W, 2*n - 2);
fmpz_one(W + (2*n - 2));
_fmpz_mod_poly_div_basecase(Qinv, W, W, 2*n - 1, Qrev, n, cinv, p);
_fmpz_poly_reverse(Qinv, Qinv, n, n);
}
for (i--; i >= 0; i--)
{
m = n;
n = a[i];
_fmpz_mod_poly_mullow(W, Q, n, Qinv, m, p, n);
_fmpz_mod_poly_mullow(Qinv + m, Qinv, m, W + m, n - m, p, n - m);
_fmpz_mod_poly_neg(Qinv + m, Qinv + m, n - m, p);
}
_fmpz_vec_clear(W, alloc);
flint_free(a);
}
}
void fmpz_mod_poly_inv_series_newton(fmpz_mod_poly_t Qinv,
const fmpz_mod_poly_t Q, slong n)
{
const fmpz *p = &(Q->p);
fmpz_t cinv;
fmpz *Qcopy;
int Qalloc;
if (Q->length >= n)
{
Qcopy = Q->coeffs;
Qalloc = 0;
}
else
{
slong i;
Qcopy = (fmpz *) flint_malloc(n * sizeof(fmpz));
for (i = 0; i < Q->length; i++)
Qcopy[i] = Q->coeffs[i];
flint_mpn_zero((mp_ptr) Qcopy + i, n - i);
Qalloc = 1;
}
fmpz_init(cinv);
fmpz_invmod(cinv, Q->coeffs, p);
if (Qinv != Q)
{
fmpz_mod_poly_fit_length(Qinv, n);
_fmpz_mod_poly_inv_series_newton(Qinv->coeffs, Qcopy, n, cinv, p);
}
else
{
fmpz *t = _fmpz_vec_init(n);
_fmpz_mod_poly_inv_series_newton(t, Qcopy, n, cinv, p);
_fmpz_vec_clear(Qinv->coeffs, Qinv->alloc);
Qinv->coeffs = t;
Qinv->alloc = n;
Qinv->length = n;
}
_fmpz_mod_poly_set_length(Qinv, n);
_fmpz_mod_poly_normalise(Qinv);
if (Qalloc)
flint_free(Qcopy);
fmpz_clear(cinv);
}