134 lines
3.5 KiB
C
134 lines
3.5 KiB
C
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/*=============================================================================
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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) 2012 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_gcdinv(fmpz *G, fmpz *S,
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const fmpz *A, slong lenA, const fmpz *B, slong lenB,
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const fmpz_t p)
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{
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fmpz *T;
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fmpz_t inv;
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slong ans;
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T = _fmpz_vec_init(lenA - 1);
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fmpz_init(inv);
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fmpz_invmod(inv, A + (lenA - 1), p);
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ans = _fmpz_mod_poly_xgcd(G, T, S, B, lenB, A, lenA, inv, p);
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fmpz_clear(inv);
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_fmpz_vec_clear(T, lenA - 1);
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return ans;
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}
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void fmpz_mod_poly_gcdinv(fmpz_mod_poly_t G, fmpz_mod_poly_t S,
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const fmpz_mod_poly_t A, const fmpz_mod_poly_t B)
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{
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const slong lenA = A->length, lenB = B->length;
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if (lenB < 2)
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{
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flint_printf("Exception (fmpz_mod_poly_gcdinv). lenB < 2.\n");
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abort();
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}
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if (lenA >= lenB)
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{
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fmpz_mod_poly_t T;
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fmpz_mod_poly_init(T, &A->p);
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fmpz_mod_poly_rem(T, A, B);
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fmpz_mod_poly_gcdinv(G, S, T, B);
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fmpz_mod_poly_clear(T);
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return;
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}
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if (lenA == 0)
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{
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fmpz_mod_poly_zero(G);
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fmpz_mod_poly_zero(S);
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}
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else
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{
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fmpz *g, *s;
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slong lenG;
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if (G == A || G == B)
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{
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g = _fmpz_vec_init(lenA);
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}
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else
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{
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fmpz_mod_poly_fit_length(G, lenA);
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g = G->coeffs;
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}
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if (S == A || S == B)
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{
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s = _fmpz_vec_init(lenB - 1);
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}
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else
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{
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fmpz_mod_poly_fit_length(S, lenB - 1);
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s = S->coeffs;
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}
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lenG = _fmpz_mod_poly_gcdinv(g, s,
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A->coeffs, lenA, B->coeffs, lenB, &A->p);
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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 = lenA;
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}
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if (S == A || S == B)
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{
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_fmpz_vec_clear(S->coeffs, S->alloc);
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S->coeffs = s;
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S->alloc = lenB - 1;
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}
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_fmpz_mod_poly_set_length(G, lenG);
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_fmpz_mod_poly_set_length(S, lenB - lenG);
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_fmpz_mod_poly_normalise(S);
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if (!fmpz_is_one(fmpz_mod_poly_lead(G)))
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{
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fmpz_t inv;
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fmpz_init(inv);
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fmpz_invmod(inv, fmpz_mod_poly_lead(G), &A->p);
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fmpz_mod_poly_scalar_mul_fmpz(G, G, inv);
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fmpz_mod_poly_scalar_mul_fmpz(S, S, inv);
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fmpz_clear(inv);
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}
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}
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}
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