157 lines
4.7 KiB
C
157 lines
4.7 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, 2012 Sebastian Pancratz
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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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#define __set(B, lenB, A, lenA) \
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do { \
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_nmod_vec_set((B), (A), (lenA)); \
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(lenB) = (lenA); \
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} while (0)
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#define __rem(R, lenR, A, lenA, B, lenB) \
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do { \
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if ((lenA) >= (lenB)) \
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{ \
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_nmod_poly_rem((R), (A), (lenA), (B), (lenB), mod); \
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(lenR) = (lenB) - 1; \
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MPN_NORM((R), (lenR)); \
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} \
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else \
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{ \
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_nmod_vec_set((R), (A), (lenA)); \
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(lenR) = (lenA); \
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} \
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} while (0)
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/*
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XXX: Incidentally, this implementation currently supports aliasing.
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But since this may change in the future, no function other than
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nmod_poly_gcd_hgcd() should rely on this.
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*/
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slong _nmod_poly_gcd_hgcd(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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const slong cutoff = FLINT_BIT_COUNT(mod.n) <= 8 ?
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NMOD_POLY_SMALL_GCD_CUTOFF : NMOD_POLY_GCD_CUTOFF;
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mp_ptr J = _nmod_vec_init(2 * lenB);
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mp_ptr R = J + lenB;
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slong lenG, lenJ, lenR;
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__rem(R, lenR, A, lenA, B, lenB);
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if (lenR == 0)
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{
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__set(G, lenG, B, lenB);
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}
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else
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{
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_nmod_poly_hgcd(NULL, NULL, G, &(lenG), J, &(lenJ), B, lenB, R, lenR, mod);
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while (lenJ != 0)
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{
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__rem(R, lenR, G, lenG, J, lenJ);
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if (lenR == 0)
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{
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__set(G, lenG, J, lenJ);
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break;
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}
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if (lenJ < cutoff)
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{
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lenG = _nmod_poly_gcd_euclidean(G, J, lenJ, R, lenR, mod);
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break;
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}
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_nmod_poly_hgcd(NULL, NULL, G, &(lenG), J, &(lenJ), J, lenJ, R, lenR, mod);
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}
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}
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_nmod_vec_clear(J);
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return lenG;
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}
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void nmod_poly_gcd_hgcd(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_hgcd(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_hgcd(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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#undef __set
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#undef __rem
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