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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. */
void
_fmpz_poly_mulhigh_classical(fmpz * res, const fmpz * poly1,
slong len1, const fmpz * poly2, slong len2,
slong start)
{
_fmpz_vec_zero(res, start);
if (len1 == 1 && len2 == 1) /* Special case if the length of both inputs is 1 */
{
if (start == 0)
fmpz_mul(res, poly1, poly2);
}
else /* Ordinary case */
{
slong i, m, n;
/* Set res[i] = poly1[i]*poly2[0] */
if (start < len1)
_fmpz_vec_scalar_mul_fmpz(res + start, poly1 + start, len1 - start,
poly2);
/* Set res[i+len1-1] = in1[len1-1]*in2[i] */
m = FLINT_MAX(len1 - 1, start);
_fmpz_vec_scalar_mul_fmpz(res + m, poly2 + m - len1 + 1,
len2 - 1 + len1 - m, poly1 + len1 - 1);
/* out[i+j] += in1[i]*in2[j] */
m = FLINT_MAX(start, len2 - 1);
for (i = m - len2 + 1; i < len1 - 1; i++)
{
n = FLINT_MAX(i + 1, start);
_fmpz_vec_scalar_addmul_fmpz(res + n, poly2 + n - i, len2 + i - n,
poly1 + i);
}
}
}
void
fmpz_poly_mulhigh_classical(fmpz_poly_t res,
const fmpz_poly_t poly1, const fmpz_poly_t poly2,
slong start)
{
slong len_out = poly1->length + poly2->length - 1;
if (poly1->length == 0 || poly2->length == 0 || start >= len_out)
{
fmpz_poly_zero(res);
return;
}
if (res == poly1 || res == poly2)
{
fmpz_poly_t temp;
fmpz_poly_init2(temp, len_out);
_fmpz_poly_mulhigh_classical(temp->coeffs, poly1->coeffs,
poly1->length, poly2->coeffs,
poly2->length, start);
fmpz_poly_swap(res, temp);
fmpz_poly_clear(temp);
}
else
{
fmpz_poly_fit_length(res, len_out);
_fmpz_poly_mulhigh_classical(res->coeffs, poly1->coeffs, poly1->length,
poly2->coeffs, poly2->length, start);
}
_fmpz_poly_set_length(res, len_out);
}