109 lines
2.8 KiB
C
109 lines
2.8 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_mod_poly.h"
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int _fmpz_mod_poly_invmod(fmpz *A,
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const fmpz *B, slong lenB,
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const fmpz *P, slong lenP, const fmpz_t p)
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{
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fmpz *G;
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slong lenG;
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FMPZ_VEC_NORM(B, lenB);
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G = _fmpz_vec_init(lenB);
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lenG = _fmpz_mod_poly_gcdinv(G, A, B, lenB, P, lenP, p);
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if (lenG == 1 && !fmpz_is_one(G + 0))
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{
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fmpz_t invG;
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fmpz_init(invG);
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fmpz_invmod(invG, G + 0, p);
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_fmpz_mod_poly_scalar_mul_fmpz(A, A, lenP - 1, invG, p);
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fmpz_clear(invG);
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}
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_fmpz_vec_clear(G, lenB);
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return (lenG == 1);
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}
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int fmpz_mod_poly_invmod(fmpz_mod_poly_t A,
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const fmpz_mod_poly_t B, const fmpz_mod_poly_t P)
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{
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const slong lenB = B->length, lenP = P->length;
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fmpz *t;
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int ans;
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if (lenP < 2)
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{
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flint_printf("Exception (fmpz_mod_poly_invmod). lenP < 2.\n");
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abort();
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}
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if (lenB == 0)
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{
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fmpz_mod_poly_zero(A);
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return 0;
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}
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if (lenB >= lenP)
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{
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fmpz_mod_poly_t T;
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fmpz_mod_poly_init(T, &B->p);
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fmpz_mod_poly_rem(T, B, P);
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ans = fmpz_mod_poly_invmod(A, T, P);
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fmpz_mod_poly_clear(T);
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return ans;
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}
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if (A != B && A != P)
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{
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fmpz_mod_poly_fit_length(A, lenP - 1);
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t = A->coeffs;
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}
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else
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{
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t = _fmpz_vec_init(lenP);
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}
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ans = _fmpz_mod_poly_invmod(t, B->coeffs, lenB, P->coeffs, lenP, &B->p);
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if (A == B || A == P)
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{
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_fmpz_vec_clear(A->coeffs, A->alloc);
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A->coeffs = t;
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A->alloc = lenP - 1;
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}
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_fmpz_mod_poly_set_length(A, lenP - 1);
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_fmpz_mod_poly_normalise(A);
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return ans;
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}
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