pqc/external/flint-2.4.3/fmpz_poly/compose_horner.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) 2010 Sebastian Pancratz
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"
void
_fmpz_poly_compose_horner(fmpz * res, const fmpz * poly1, slong len1,
const fmpz * poly2, slong len2)
{
if (len1 == 1)
{
fmpz_set(res, poly1);
}
else
{
const slong alloc = (len1 - 1) * (len2 - 1) + 1;
slong i = len1 - 1, lenr;
fmpz * t = _fmpz_vec_init(alloc);
/*
Perform the first two steps as one,
"res = a(m) * poly2 + a(m-1)".
*/
{
lenr = len2;
_fmpz_vec_scalar_mul_fmpz(res, poly2, len2, poly1 + i);
i--;
fmpz_add(res, res, poly1 + i);
}
while (i--)
{
_fmpz_poly_mul(t, res, lenr, poly2, len2);
lenr += len2 - 1;
_fmpz_poly_add(res, t, lenr, poly1 + i, 1);
}
_fmpz_vec_clear(t, alloc);
}
}
void
fmpz_poly_compose_horner(fmpz_poly_t res,
const fmpz_poly_t poly1, const fmpz_poly_t poly2)
{
const slong len1 = poly1->length;
const slong len2 = poly2->length;
if (len1 == 0)
{
fmpz_poly_zero(res);
}
else if (len1 == 1 || len2 == 0)
{
fmpz_poly_set_fmpz(res, poly1->coeffs);
}
else
{
const slong lenr = (len1 - 1) * (len2 - 1) + 1;
if ((res != poly1) && (res != poly2))
{
fmpz_poly_fit_length(res, lenr);
_fmpz_poly_compose_horner(res->coeffs, poly1->coeffs, len1,
poly2->coeffs, len2);
_fmpz_poly_set_length(res, lenr);
}
else
{
fmpz_poly_t t;
fmpz_poly_init2(t, lenr);
_fmpz_poly_compose_horner(t->coeffs, poly1->coeffs, len1,
poly2->coeffs, len2);
_fmpz_poly_set_length(t, lenr);
fmpz_poly_swap(res, t);
fmpz_poly_clear(t);
}
_fmpz_poly_normalise(res);
}
}