pqc/external/flint-2.4.3/fmpz_poly/sqrlow_classical.c
2014-05-24 23:16:06 +02:00

92 lines
2.6 KiB
C

/*=============================================================================
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) 2011 Sebastian Pancratz
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"
/*
Assumes len > 0 and 0 < n <= 2 * len - 1.
*/
void _fmpz_poly_sqrlow_classical(fmpz *rop, const fmpz *op, slong len, slong n)
{
if (len == 1 || n == 1) /* Special case */
{
fmpz_mul(rop, op, op);
}
else /* Ordinary case */
{
slong i;
_fmpz_vec_scalar_mul_fmpz(rop, op, FLINT_MIN(len, n), op);
_fmpz_vec_scalar_mul_fmpz(rop + len, op + 1, n - len, op + len - 1);
for (i = 1; i < len - 1; i++)
_fmpz_vec_scalar_addmul_fmpz(rop + i + 1,
op + 1, FLINT_MIN(i - 1, n - (i + 1)), op + i);
for (i = 1; i < FLINT_MIN(2 * len - 2, n); i++)
fmpz_mul_ui(rop + i, rop + i, 2);
for (i = 1; i < FLINT_MIN(len - 1, (n + 1) / 2); i++)
fmpz_addmul(rop + 2 * i, op + i, op + i);
}
}
void
fmpz_poly_sqrlow_classical(fmpz_poly_t res, const fmpz_poly_t poly, slong n)
{
slong len = poly->length;
if (len == 0 || n == 0)
{
fmpz_poly_zero(res);
return;
}
n = FLINT_MIN(2 * len - 1, n);
if (res == poly)
{
fmpz_poly_t t;
fmpz_poly_init2(t, n);
_fmpz_poly_sqrlow_classical(t->coeffs, poly->coeffs, len, n);
fmpz_poly_swap(res, t);
fmpz_poly_clear(t);
}
else
{
fmpz_poly_fit_length(res, n);
_fmpz_poly_sqrlow_classical(res->coeffs, poly->coeffs, len, n);
}
_fmpz_poly_set_length(res, n);
_fmpz_poly_normalise(res);
}