150 lines
3.8 KiB
C
150 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) 2011 William Hart
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******************************************************************************/
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#include <stdlib.h>
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#include "nmod_poly.h"
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#include "mpn_extras.h"
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slong _nmod_poly_gcd_euclidean(mp_ptr G, mp_srcptr A, slong lenA,
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mp_srcptr B, slong lenB, nmod_t mod)
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{
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slong steps;
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slong lenR1, lenR2 = 0, lenG = 0;
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mp_ptr F, R1, R2, R3 = G, T;
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if (lenB == 1)
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{
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G[0] = B[0];
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return 1;
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}
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F = _nmod_vec_init(2*lenB - 3);
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R1 = F;
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R2 = R1 + lenB - 1;
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_nmod_poly_rem(R1, A, lenA, B, lenB, mod);
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lenR1 = lenB - 1;
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MPN_NORM(R1, lenR1);
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if (lenR1 > 1)
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{
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_nmod_poly_rem(R2, B, lenB, R1, lenR1, mod);
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lenR2 = lenR1 - 1;
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MPN_NORM(R2, lenR2);
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}
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else
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{
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if (lenR1 == 0)
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{
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flint_mpn_copyi(G, B, lenB);
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_nmod_vec_clear(F);
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return lenB;
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}
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else
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{
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G[0] = R1[0];
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_nmod_vec_clear(F);
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return 1;
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}
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}
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for (steps = 2; lenR2 > 1; steps++)
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{
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_nmod_poly_rem(R3, R1, lenR1, R2, lenR2, mod);
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lenR1 = lenR2--;
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MPN_NORM(R3, lenR2);
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T = R1; R1 = R2; R2 = R3; R3 = T;
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}
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if (lenR2 == 1)
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{
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lenG = 1;
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if (steps % 3)
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G[0] = R2[0];
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}
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else
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{
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lenG = lenR1;
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if (steps % 3 != 1)
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flint_mpn_copyi(G, R1, lenR1);
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}
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_nmod_vec_clear(F);
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return lenG;
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}
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void nmod_poly_gcd_euclidean(nmod_poly_t G,
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const nmod_poly_t A, const nmod_poly_t B)
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{
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if (A->length < B->length)
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{
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nmod_poly_gcd_euclidean(G, B, A);
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}
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else /* lenA >= lenB >= 0 */
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{
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slong lenA = A->length, lenB = B->length, lenG;
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nmod_poly_t tG;
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mp_ptr g;
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if (lenA == 0) /* lenA = lenB = 0 */
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{
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nmod_poly_zero(G);
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}
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else if (lenB == 0) /* lenA > lenB = 0 */
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{
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nmod_poly_make_monic(G, A);
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}
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else /* lenA >= lenB >= 1 */
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{
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if (G == A || G == B)
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{
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nmod_poly_init2(tG, A->mod.n, FLINT_MIN(lenA, lenB));
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g = tG->coeffs;
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}
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else
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{
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nmod_poly_fit_length(G, FLINT_MIN(lenA, lenB));
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g = G->coeffs;
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}
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lenG = _nmod_poly_gcd_euclidean(g, A->coeffs, lenA,
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B->coeffs, lenB, A->mod);
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if (G == A || G == B)
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{
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nmod_poly_swap(tG, G);
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nmod_poly_clear(tG);
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}
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G->length = lenG;
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if (G->length == 1)
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G->coeffs[0] = 1;
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else
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nmod_poly_make_monic(G, G);
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}
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}
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}
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