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/*
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 "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"
/* Assumes poly1 and poly2 are not length 0 and len1 >= len2. */
void
_fmpz_poly_mulmid_classical(fmpz * res, const fmpz * poly1,
slong len1, const fmpz * poly2, slong len2)
{
if ((len1 == 1) && (len2 == 1)) /* Special case if the length of both inputs is 1 */
{
fmpz_mul(res, poly1, poly2);
}
else /* Ordinary case */
{
slong i;
/* Set res[i] = poly1[i]*poly2[0] */
_fmpz_vec_scalar_mul_fmpz(res, poly1 + len2 - 1, len1 - len2 + 1,
poly2);
/* out[i+j] += in1[i]*in2[j] */
for (i = 0; i < len2 - 1; i++)
_fmpz_vec_scalar_addmul_fmpz(res, poly2 + len2 - i - 1,
FLINT_MIN(i + 1, len1 - len2 + 1),
poly1 + i);
for (; i < len1 - 1; i++)
_fmpz_vec_scalar_addmul_fmpz(res + i - len2 + 2, poly2 + 1,
FLINT_MIN(len2 - 1, len1 - i - 1),
poly1 + i);
}
}
void
fmpz_poly_mulmid_classical(fmpz_poly_t res,
const fmpz_poly_t poly1, const fmpz_poly_t poly2)
{
slong len_out;
if (poly1->length == 0 || poly2->length == 0)
{
fmpz_poly_zero(res);
return;
}
len_out = poly1->length - poly2->length + 1;
if (res == poly1 || res == poly2)
{
fmpz_poly_t temp;
fmpz_poly_init2(temp, len_out);
_fmpz_poly_mulmid_classical(temp->coeffs, poly1->coeffs, poly1->length,
poly2->coeffs, poly2->length);
fmpz_poly_swap(res, temp);
fmpz_poly_clear(temp);
}
else
{
fmpz_poly_fit_length(res, len_out);
_fmpz_poly_mulmid_classical(res->coeffs, poly1->coeffs, poly1->length,
poly2->coeffs, poly2->length);
}
_fmpz_poly_set_length(res, len_out);
_fmpz_poly_normalise(res);
}