pqc/external/flint-2.4.3/fmpz_poly/mullow_classical.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
This file is part of FLINT.
FLINT is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
FLINT is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2008, 2009 William Hart
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"
/*
Assumes poly1 and poly2 are not length 0 and 0 < n <= len1 + len2 - 1.
*/
void
_fmpz_poly_mullow_classical(fmpz * res, const fmpz * poly1, slong len1,
const fmpz * poly2, slong len2, slong n)
{
if ((len1 == 1 && len2 == 1) || n == 1) /* Special case if the length of output 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, FLINT_MIN(len1, n), poly2);
/* Set res[i+len1-1] = in1[len1-1]*in2[i] */
if (n > len1)
_fmpz_vec_scalar_mul_fmpz(res + len1, poly2 + 1, n - len1,
poly1 + len1 - 1);
/* out[i+j] += in1[i]*in2[j] */
for (i = 0; i < FLINT_MIN(len1, n) - 1; i++)
_fmpz_vec_scalar_addmul_fmpz(res + i + 1, poly2 + 1,
FLINT_MIN(len2, n - i) - 1,
poly1 + i);
}
}
void
fmpz_poly_mullow_classical(fmpz_poly_t res, const fmpz_poly_t poly1,
const fmpz_poly_t poly2, slong n)
{
slong len_out;
if (poly1->length == 0 || poly2->length == 0 || n == 0)
{
fmpz_poly_zero(res);
return;
}
len_out = poly1->length + poly2->length - 1;
if (n > len_out)
n = len_out;
if (res == poly1 || res == poly2)
{
fmpz_poly_t t;
fmpz_poly_init2(t, n);
_fmpz_poly_mullow_classical(t->coeffs, poly1->coeffs, poly1->length,
poly2->coeffs, poly2->length, n);
fmpz_poly_swap(res, t);
fmpz_poly_clear(t);
}
else
{
fmpz_poly_fit_length(res, n);
_fmpz_poly_mullow_classical(res->coeffs, poly1->coeffs, poly1->length,
poly2->coeffs, poly2->length, n);
}
_fmpz_poly_set_length(res, n);
_fmpz_poly_normalise(res);
}