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/*
Copyright (C) 2007, David Howden.
Copyright (C) 2010 William Hart
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 "nmod.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
void
_nmod_poly_sub(nn_ptr res, nn_srcptr poly1, slong len1, nn_srcptr poly2,
slong len2, nmod_t mod)
{
slong i, min = FLINT_MIN(len1, len2);
_nmod_vec_sub(res, poly1, poly2, min, mod);
if (poly1 != res) /* Copy any remaining coefficients from poly1 */
for (i = min; i < len1; i++)
res[i] = poly1[i];
/*
Careful, it is *always* necessary to negate coeffs from poly2,
even if this is already res.
*/
for (i = min; i < len2; i++)
res[i] = nmod_neg(poly2[i], mod);
}
void
nmod_poly_sub(nmod_poly_t res, const nmod_poly_t poly1,
const nmod_poly_t poly2)
{
slong max = FLINT_MAX(poly1->length, poly2->length);
nmod_poly_fit_length(res, max);
_nmod_poly_sub(res->coeffs, poly1->coeffs, poly1->length, poly2->coeffs,
poly2->length, poly1->mod);
res->length = max;
_nmod_poly_normalise(res); /* there may have been cancellation */
}