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/*
Copyright (C) 2011, 2014 William Hart
Copyright (C) 2011, 2012 Sebastian Pancratz
Copyright (C) 2024 Fredrik Johansson
This file is part of FLINT.
FLINT is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License (LGPL) as published
by the Free Software Foundation; either version 3 of the License, or
(at your option) any later version. See <https://www.gnu.org/licenses/>.
*/
#include "fmpz.h"
#include "fmpz_mod.h"
#include "fmpz_mod_poly.h"
#include "gr_poly.h"
void _fmpz_mod_poly_resultant(fmpz_t res, const fmpz *A, slong lenA,
const fmpz *B, slong lenB, const fmpz_mod_ctx_t ctx)
{
gr_ctx_t gr_ctx;
_gr_ctx_init_fmpz_mod_from_ref(gr_ctx, ctx);
GR_MUST_SUCCEED(_gr_poly_resultant(res, A, lenA, B, lenB, gr_ctx));
}
void fmpz_mod_poly_resultant(fmpz_t res, const fmpz_mod_poly_t A,
const fmpz_mod_poly_t B, const fmpz_mod_ctx_t ctx)
{
if (A->length == 0 || B->length == 0)
{
fmpz_zero(res);
}
else if (A->length < B->length)
{
fmpz_mod_poly_resultant(res, B, A, ctx);
if (((A->length | B->length) & 1) == 0)
fmpz_mod_neg(res, res, ctx);
}
else /* lenA >= lenB >= 0 */
{
slong lenA = A->length, lenB = B->length;
/* lenA >= lenB >= 1 */
_fmpz_mod_poly_resultant(res, A->coeffs, lenA, B->coeffs, lenB, ctx);
}
}