152 lines
4.3 KiB
C
152 lines
4.3 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 Sebastian Pancratz
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******************************************************************************/
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#include <stdlib.h>
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#include "fmpz_vec.h"
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#include "fmpz_mod_poly.h"
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slong _fmpz_mod_poly_gcd_euclidean(fmpz *G, const fmpz *A, slong lenA,
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const fmpz *B, slong lenB,
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const fmpz_t invB, const fmpz_t p)
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{
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if (lenB == 1)
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{
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fmpz_one(G);
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return 1;
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}
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else /* lenA >= lenB > 1 */
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{
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const slong lenW = FLINT_MAX(lenA - lenB + 1, lenB) + lenA + 2 * lenB;
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fmpz_t invR3;
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fmpz *Q, *R1, *R2, *R3, *T, *W;
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slong lenR2, lenR3;
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W = _fmpz_vec_init(lenW);
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Q = W;
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R1 = W + FLINT_MAX(lenA - lenB + 1, lenB);
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R2 = R1 + lenA;
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R3 = R2 + lenB;
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_fmpz_mod_poly_divrem(Q, R1, A, lenA, B, lenB, invB, p);
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lenR3 = lenB - 1;
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FMPZ_VEC_NORM(R1, lenR3);
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if (lenR3 == 0)
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{
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_fmpz_vec_set(G, B, lenB);
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_fmpz_vec_clear(W, lenW);
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return lenB;
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}
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fmpz_init(invR3);
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T = R3;
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R3 = R1;
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R1 = T;
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_fmpz_vec_set(R2, B, lenB);
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lenR2 = lenB;
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do
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{
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fmpz_invmod(invR3, R3 + (lenR3 - 1), p);
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_fmpz_mod_poly_divrem(Q, R1, R2, lenR2, R3, lenR3, invR3, p);
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lenR2 = lenR3--;
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FMPZ_VEC_NORM(R1, lenR3);
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T = R2; R2 = R3; R3 = R1; R1 = T;
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}
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while (lenR3 > 0);
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_fmpz_vec_set(G, R2, lenR2);
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_fmpz_vec_clear(W, lenW);
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fmpz_clear(invR3);
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return lenR2;
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}
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}
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void fmpz_mod_poly_gcd_euclidean(fmpz_mod_poly_t G,
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const fmpz_mod_poly_t A,
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const fmpz_mod_poly_t B)
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{
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if (A->length < B->length)
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{
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fmpz_mod_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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const slong lenA = A->length, lenB = B->length;
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slong lenG;
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fmpz *g;
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if (lenA == 0) /* lenA = lenB = 0 */
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{
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fmpz_mod_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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fmpz_mod_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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fmpz_t invB;
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if (G == A || G == B)
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{
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g = _fmpz_vec_init(FLINT_MIN(lenA, lenB));
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}
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else
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{
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fmpz_mod_poly_fit_length(G, FLINT_MIN(lenA, lenB));
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g = G->coeffs;
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}
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fmpz_init(invB);
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fmpz_invmod(invB, fmpz_mod_poly_lead(B), &(B->p));
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lenG = _fmpz_mod_poly_gcd_euclidean(g, A->coeffs, lenA,
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B->coeffs, lenB, invB, &(B->p));
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fmpz_clear(invB);
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if (G == A || G == B)
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{
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_fmpz_vec_clear(G->coeffs, G->alloc);
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G->coeffs = g;
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G->alloc = FLINT_MIN(lenA, lenB);
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G->length = FLINT_MIN(lenA, lenB);
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}
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_fmpz_mod_poly_set_length(G, lenG);
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if (lenG == 1)
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fmpz_one(G->coeffs);
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else
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fmpz_mod_poly_make_monic(G, G);
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}
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}
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}
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