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

156 lines
4.0 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
Copyright (C) 2011 Fredrik Johansson
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
#include "ulong_extras.h"
void
_nmod_poly_powmod_ui_binexp(mp_ptr res, mp_srcptr poly,
ulong e, mp_srcptr f, slong lenf, nmod_t mod)
{
mp_ptr T, Q;
slong lenT, lenQ;
int i;
if (lenf == 2)
{
res[0] = n_powmod2_ui_preinv(poly[0], e, mod.n, mod.ninv);
return;
}
lenT = 2 * lenf - 3;
lenQ = FLINT_MAX(lenT - lenf + 1, 1);
T = _nmod_vec_init(lenT + lenQ);
Q = T + lenT;
_nmod_vec_set(res, poly, lenf - 1);
for (i = ((int) FLINT_BIT_COUNT(e) - 2); i >= 0; i--)
{
_nmod_poly_mul(T, res, lenf - 1, res, lenf - 1, mod);
_nmod_poly_divrem(Q, res, T, 2 * lenf - 3, f, lenf, mod);
if (e & (UWORD(1) << i))
{
_nmod_poly_mul(T, res, lenf - 1, poly, lenf - 1, mod);
_nmod_poly_divrem(Q, res, T, 2 * lenf - 3, f, lenf, mod);
}
}
_nmod_vec_clear(T);
}
void
nmod_poly_powmod_ui_binexp(nmod_poly_t res,
const nmod_poly_t poly, ulong e,
const nmod_poly_t f)
{
mp_ptr p;
slong len = poly->length;
slong lenf = f->length;
slong trunc = lenf - 1;
int pcopy = 0;
if (lenf == 0)
{
flint_printf("Exception (nmod_poly_powmod). Divide by zero.\n");
abort();
}
if (len >= lenf)
{
nmod_poly_t t, r;
nmod_poly_init_preinv(t, res->mod.n, res->mod.ninv);
nmod_poly_init_preinv(r, res->mod.n, res->mod.ninv);
nmod_poly_divrem(t, r, poly, f);
nmod_poly_powmod_ui_binexp(res, r, e, f);
nmod_poly_clear(t);
nmod_poly_clear(r);
return;
}
if (e <= 2)
{
if (e == UWORD(0))
{
nmod_poly_fit_length(res, 1);
res->coeffs[0] = UWORD(1);
res->length = 1;
}
else if (e == UWORD(1))
{
nmod_poly_set(res, poly);
}
else
nmod_poly_mulmod(res, poly, poly, f);
return;
}
if (lenf == 1 || len == 0)
{
nmod_poly_zero(res);
return;
}
if (len < trunc)
{
p = _nmod_vec_init(trunc);
flint_mpn_copyi(p, poly->coeffs, len);
flint_mpn_zero(p + len, trunc - len);
pcopy = 1;
} else
p = poly->coeffs;
if ((res == poly && !pcopy) || (res == f))
{
nmod_poly_t t;
nmod_poly_init2(t, poly->mod.n, trunc);
_nmod_poly_powmod_ui_binexp(t->coeffs,
p, e, f->coeffs, lenf, poly->mod);
nmod_poly_swap(res, t);
nmod_poly_clear(t);
}
else
{
nmod_poly_fit_length(res, trunc);
_nmod_poly_powmod_ui_binexp(res->coeffs,
p, e, f->coeffs, lenf, poly->mod);
}
if (pcopy)
_nmod_vec_clear(p);
res->length = trunc;
_nmod_poly_normalise(res);
}