pqc/external/flint-2.4.3/nmod_poly/pow_trunc_binexp.c

174 lines
4.5 KiB
C
Raw Normal View History

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
Copyright (C) 2010 William Hart
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
void
_nmod_poly_pow_trunc_binexp(mp_ptr res, mp_srcptr poly,
ulong e, slong trunc, nmod_t mod)
{
ulong bit = ~((~UWORD(0)) >> 1);
mp_ptr v = _nmod_vec_init(trunc);
mp_ptr R, S, T;
/*
Set bits to the bitmask with a 1 one place lower than the msb of e
*/
while ((bit & e) == UWORD(0))
bit >>= 1;
bit >>= 1;
/*
Trial run without any polynomial arithmetic to determine the parity
of the number of swaps; then set R and S accordingly
*/
{
unsigned int swaps = 0U;
ulong bit2 = bit;
if ((bit2 & e))
swaps = ~swaps;
while (bit2 >>= 1)
if ((bit2 & e) == UWORD(0))
swaps = ~swaps;
if (swaps == 0U)
{
R = res;
S = v;
}
else
{
R = v;
S = res;
}
}
/*
We unroll the first step of the loop, referring to {poly, len}
*/
_nmod_poly_mullow(R, poly, trunc, poly, trunc, trunc, mod);
if ((bit & e))
{
_nmod_poly_mullow(S, R, trunc, poly, trunc, trunc, mod);
T = R;
R = S;
S = T;
}
while ((bit >>= 1))
{
if ((bit & e))
{
_nmod_poly_mullow(S, R, trunc, R, trunc, trunc, mod);
_nmod_poly_mullow(R, S, trunc, poly, trunc, trunc, mod);
}
else
{
_nmod_poly_mullow(S, R, trunc, R, trunc, trunc, mod);
T = R;
R = S;
S = T;
}
}
_nmod_vec_clear(v);
}
void
nmod_poly_pow_trunc_binexp(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_binexp(res->coeffs, p, e, trunc, poly->mod);
}
else
{
nmod_poly_t t;
nmod_poly_init2(t, poly->mod.n, trunc);
_nmod_poly_pow_trunc_binexp(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);
}