153 lines
3.8 KiB
C
153 lines
3.8 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) 2007, 2008 William Hart
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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 "mpn_extras.h"
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#include "nmod_vec.h"
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#include "nmod_poly.h"
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mp_limb_t
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_nmod_poly_resultant_euclidean(mp_srcptr poly1, slong len1,
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mp_srcptr poly2, slong len2, nmod_t mod)
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{
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if (poly1 == poly2)
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{
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return 0;
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}
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else if (len2 == 1)
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{
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if (len1 == 1)
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{
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return 1;
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}
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else if (len1 == 2)
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{
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return poly2[0];
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}
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else
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{
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return n_powmod2_ui_preinv(poly2[0], len1 - 1, mod.n, mod.ninv);
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}
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}
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else /* len1 >= len2 >= 2 */
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{
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mp_limb_t res = 1;
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mp_ptr u, v, r, t, w;
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slong l0, l1, l2;
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mp_limb_t lc;
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w = _nmod_vec_init(3 * len1);
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u = w;
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v = w + len1;
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r = v + len1;
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_nmod_vec_set(u, poly1, len1);
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_nmod_vec_set(v, poly2, len2);
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l1 = len1;
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l2 = len2;
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do
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{
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l0 = l1;
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l1 = l2;
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lc = v[l1 - 1];
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_nmod_poly_rem(r, u, l0, v, l1, mod);
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l2 = l1 - 1;
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MPN_NORM(r, l2);
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{
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t = u;
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u = v;
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v = r;
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r = t;
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}
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if (l2 >= 1)
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{
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lc = n_powmod2_preinv(lc, l0 - l2, mod.n, mod.ninv);
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res = n_mulmod2_preinv(res, lc, mod.n, mod.ninv);
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if (((l0 | l1) & 1) == 0)
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{
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res = nmod_neg(res, mod);
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}
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}
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else
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{
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if (l1 == 1)
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{
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lc = n_powmod2_preinv(lc, l0 - 1, mod.n, mod.ninv);
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res = n_mulmod2_preinv(res, lc, mod.n, mod.ninv);
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}
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else
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{
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res = 0;
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}
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}
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}
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while (l2 > 0);
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_nmod_vec_clear(w);
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return res;
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}
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}
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mp_limb_t
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nmod_poly_resultant_euclidean(const nmod_poly_t f, const nmod_poly_t g)
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{
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const slong len1 = f->length;
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const slong len2 = g->length;
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mp_limb_t r;
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if (len1 == 0 || len2 == 0)
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{
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r = 0;
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}
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else
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{
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if (len1 >= len2)
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{
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r = _nmod_poly_resultant_euclidean(f->coeffs, len1,
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g->coeffs, len2, f->mod);
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}
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else
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{
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r = _nmod_poly_resultant_euclidean(g->coeffs, len2,
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f->coeffs, len1, f->mod);
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if (((len1 | len2) & WORD(1)) == WORD(0))
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r = nmod_neg(r, f->mod);
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}
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}
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return r;
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}
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