131 lines
3.2 KiB
C
131 lines
3.2 KiB
C
/*=============================================================================
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This file is part of FLINT.
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FLINT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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FLINT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with FLINT; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2011 William Hart
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Copyright (C) 2011 Fredrik Johansson
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Copyright (C) 2011 Sebastian Pancratz
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******************************************************************************/
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#include <stdlib.h>
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#include <gmp.h>
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#include "flint.h"
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#include "nmod_vec.h"
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#include "nmod_poly.h"
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#include "ulong_extras.h"
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#define NMOD_POLY_INV_NEWTON_CUTOFF 400
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void
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_nmod_poly_inv_series_newton(mp_ptr Qinv, mp_srcptr Q, slong n, nmod_t mod)
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{
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if (n < NMOD_POLY_INV_NEWTON_CUTOFF)
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{
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_nmod_poly_inv_series_basecase(Qinv, Q, n, mod);
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}
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else
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{
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slong *a, i, m;
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mp_ptr W;
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for (i = 1; (WORD(1) << i) < n; i++) ;
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W = flint_malloc(n * sizeof(mp_limb_t) + i * sizeof(slong));
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a = (slong *) (W + n);
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a[i = 0] = n;
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while (n >= NMOD_POLY_INV_NEWTON_CUTOFF)
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a[++i] = (n = (n + 1) / 2);
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_nmod_poly_inv_series_basecase(Qinv, Q, n, mod);
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for (i--; i >= 0; i--)
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{
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m = n;
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n = a[i];
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_nmod_poly_mullow(W, Q, n, Qinv, m, n, mod);
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_nmod_poly_mullow(Qinv + m, Qinv, m, W + m, n - m, n - m, mod);
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_nmod_vec_neg(Qinv + m, Qinv + m, n - m, mod);
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}
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flint_free(W);
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}
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}
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void
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nmod_poly_inv_series_newton(nmod_poly_t Qinv, const nmod_poly_t Q, slong n)
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{
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const slong Qlen = Q->length;
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mp_ptr q, qinv;
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if (n == 0 || Q->length == 0 || Q->coeffs[0] == 0)
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{
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flint_printf("Exception (nmod_poly_inv_series_newton). Division by zero.\n");
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abort();
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}
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if (Qlen < n)
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{
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q = _nmod_vec_init(n);
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flint_mpn_copyi(q, Q->coeffs, Qlen);
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flint_mpn_zero(q + Qlen, n - Qlen);
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}
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else
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{
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q = Q->coeffs;
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}
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if (Q == Qinv && Qlen >= n)
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{
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qinv = _nmod_vec_init(n);
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}
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else
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{
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nmod_poly_fit_length(Qinv, n);
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qinv = Qinv->coeffs;
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}
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_nmod_poly_inv_series_newton(qinv, q, n, Q->mod);
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if (Q == Qinv && Qlen >= n)
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{
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flint_free(Qinv->coeffs);
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Qinv->coeffs = qinv;
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Qinv->alloc = n;
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Qinv->length = n;
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}
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else
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{
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Qinv->length = n;
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}
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if (Qlen < n)
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{
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_nmod_vec_clear(q);
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}
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_nmod_poly_normalise(Qinv);
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}
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