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

105 lines
3.1 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) 2010 Sebastian Pancratz
Copyright (C) 2010 William Hart
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
void
_nmod_poly_pow_trunc(mp_ptr res, mp_srcptr poly,
ulong e, slong trunc, nmod_t mod)
{
_nmod_poly_pow_trunc_binexp(res, poly, e, trunc, mod);
}
void
nmod_poly_pow_trunc(nmod_poly_t res,
const nmod_poly_t poly, ulong e, slong trunc)
{
const slong len = poly->length;
mp_ptr p;
int pcopy = 0;
if (len < 2 || e < UWORD(3) || trunc == 0)
{
if (len == 0 || trunc == 0)
nmod_poly_zero(res);
else if (len == 1)
{
nmod_poly_fit_length(res, 1);
res->coeffs[0] = n_powmod2_ui_preinv(poly->coeffs[0], e,
poly->mod.n, poly->mod.ninv);
res->length = 1;
_nmod_poly_normalise(res);
}
else if (e == UWORD(0))
{
nmod_poly_set_coeff_ui(res, 0, UWORD(1));
res->length = 1;
_nmod_poly_normalise(res);
}
else if (e == UWORD(1))
{
nmod_poly_set(res, poly);
nmod_poly_truncate(res, trunc);
}
else /* e == UWORD(2) */
nmod_poly_mullow(res, poly, poly, trunc);
return;
}
if (poly->length < trunc)
{
p = _nmod_vec_init(trunc);
flint_mpn_copyi(p, poly->coeffs, poly->length);
flint_mpn_zero(p + poly->length, trunc - poly->length);
pcopy = 1;
} else
p = poly->coeffs;
if (res != poly || pcopy)
{
nmod_poly_fit_length(res, trunc);
_nmod_poly_pow_trunc(res->coeffs, p, e, trunc, poly->mod);
}
else
{
nmod_poly_t t;
nmod_poly_init2(t, poly->mod.n, trunc);
_nmod_poly_pow_trunc(t->coeffs, p, e, trunc, poly->mod);
nmod_poly_swap(res, t);
nmod_poly_clear(t);
}
if (pcopy)
_nmod_vec_clear(p);
res->length = trunc;
_nmod_poly_normalise(res);
}