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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 <gmp.h>
#include "ulong_extras.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
/* Assumes poly1 and poly2 are not length 0. */
void
_nmod_poly_mulhigh_classical(nn_ptr res, nn_srcptr poly1,
slong len1, nn_srcptr poly2, slong len2, slong start,
nmod_t mod)
{
slong m, n;
_nmod_vec_zero(res, start);
if (len1 == 1) /* Special case if the length of both inputs is 1 */
{
if (start == 0)
res[0] = n_mulmod2_preinv(poly1[0], poly2[0], mod.n, mod.ninv);
}
else /* Ordinary case */
{
slong i;
slong bits = FLINT_BITS - (slong) mod.norm;
slong log_len = FLINT_BIT_COUNT(len2);
if (2 * bits + log_len <= FLINT_BITS)
{
/* Set res[i] = poly1[i]*poly2[0] */
if (start < len1)
mpn_mul_1(res + start, poly1 + start, len1 - start, poly2[0]);
if (len2 != 1)
{
/* Set res[i+len1-1] = in1[len1-1]*in2[i] */
m = FLINT_MAX(len1 - 1, start);
FLINT_ASSERT(len2 - 1 + len1 - m > 0);
mpn_mul_1(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);
mpn_addmul_1(res + n, poly2 + n - i, len2 + i - n,
poly1[i]);
}
}
_nmod_vec_reduce(res, res, len1 + len2 - 1, mod);
}
else
{
/* Set res[i] = poly1[i]*poly2[0] */
if (start < len1)
_nmod_vec_scalar_mul_nmod(res + start, poly1 + start, len1 - start,
poly2[0], mod);
if (len2 == 1)
return;
/* Set res[i+len1-1] = in1[len1-1]*in2[i] */
m = FLINT_MAX(len1 - 1, start);
_nmod_vec_scalar_mul_nmod(res + m, poly2 + m - len1 + 1,
len2 - 1 + len1 - m, poly1[len1 - 1], mod);
/* 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);
_nmod_vec_scalar_addmul_nmod(res + n, poly2 + n - i, len2 + i - n,
poly1[i], mod);
}
}
}
}
void
nmod_poly_mulhigh_classical(nmod_poly_t res,
const nmod_poly_t poly1, const nmod_poly_t poly2,
slong start)
{
slong len_out = poly1->length + poly2->length - 1;
if (poly1->length == 0 || poly2->length == 0 || start >= len_out)
{
nmod_poly_zero(res);
return;
}
if (res == poly1 || res == poly2)
{
nmod_poly_t temp;
nmod_poly_init2_preinv(temp, poly1->mod.n, poly1->mod.ninv, len_out);
if (poly1->length >= poly2->length)
_nmod_poly_mulhigh_classical(temp->coeffs, poly1->coeffs,
poly1->length, poly2->coeffs,
poly2->length, start, poly1->mod);
else
_nmod_poly_mulhigh_classical(temp->coeffs, poly2->coeffs,
poly2->length, poly1->coeffs,
poly1->length, start, poly1->mod);
nmod_poly_swap(res, temp);
nmod_poly_clear(temp);
}
else
{
nmod_poly_fit_length(res, len_out);
if (poly1->length >= poly2->length)
_nmod_poly_mulhigh_classical(res->coeffs, poly1->coeffs,
poly1->length, poly2->coeffs,
poly2->length, start, poly1->mod);
else
_nmod_poly_mulhigh_classical(res->coeffs, poly2->coeffs,
poly2->length, poly1->coeffs,
poly1->length, start, poly1->mod);
}
res->length = len_out;
_nmod_poly_normalise(res);
}