pqc/external/flint-2.4.3/fmpz_mod_poly/powmod_x_fmpz_preinv.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
Copyright (C) 2010 William Hart
Copyright (C) 2011 Fredrik Johansson
Copyright (C) 2012 Lina Kulakova
Copyright (C) 2013 Martin Lee
******************************************************************************/
#undef ulong
#define ulong ulongxx/* interferes with system includes */
#include <stdlib.h>
#undef ulong
#include <gmp.h>
#define ulong mp_limb_t
#include "flint.h"
#include "fmpz_vec.h"
#include "fmpz_mod_poly.h"
#include "long_extras.h"
void
_fmpz_mod_poly_powmod_x_fmpz_preinv(fmpz * res, const fmpz_t e, const fmpz * f,
slong lenf, const fmpz* finv, slong lenfinv,
const fmpz_t p)
{
fmpz * T, * Q;
slong lenT, lenQ;
slong i, window, l, c;
lenT = 2 * lenf - 3;
lenQ = lenT - lenf + 1;
T = _fmpz_vec_init(lenT + lenQ);
Q = T + lenT;
fmpz_one (res);
l = z_sizeinbase (lenf - 1, 2) - 2;
window = WORD(0);
window = (WORD(1) << l);
c = l;
i = fmpz_sizeinbase(e, 2) - 2;
if (i <= l)
{
window = WORD(0);
window = (WORD(1) << i);
c = i;
l = i;
}
if (c == 0)
{
_fmpz_mod_poly_shift_left(T, res, lenf - 1, window);
_fmpz_mod_poly_divrem_newton_n_preinv(Q, res, T, lenf - 1 + window, f,
lenf, finv, lenfinv, p);
c = l + 1;
window = WORD(0);
}
for (; i >= 0; i--)
{
_fmpz_mod_poly_sqr(T, res, lenf - 1, p);
_fmpz_mod_poly_divrem_newton_n_preinv(Q, res, T, 2 * lenf - 3, f, lenf,
finv, lenfinv, p);
c--;
if (fmpz_tstbit(e, i))
{
if (window == WORD(0) && i <= l - 1)
c = i;
if ( c >= 0)
window = window | (WORD(1) << c);
}
else if (window == WORD(0))
c = l + 1;
if (c == 0)
{
_fmpz_mod_poly_shift_left(T, res, lenf - 1, window);
_fmpz_mod_poly_divrem_newton_n_preinv(Q, res, T, lenf - 1 + window,
f, lenf, finv, lenfinv, p);
c = l + 1;
window = WORD(0);
}
}
_fmpz_vec_clear(T, lenT + lenQ);
}
void
fmpz_mod_poly_powmod_x_fmpz_preinv(fmpz_mod_poly_t res, const fmpz_t e,
const fmpz_mod_poly_t f, const fmpz_mod_poly_t finv)
{
slong lenf = f->length;
slong trunc = lenf - 1;
fmpz_mod_poly_t tmp;
if (lenf == 0)
{
flint_printf("Exception (fmpz_mod_poly_powmod_x_fmpz_preinv)."
"Divide by zero\n");
abort();
}
if (fmpz_sgn(e) < 0)
{
flint_printf("Exception (fmpz_mod_poly_powmod_x_fmpz_preinv)."
"Negative exp not implemented\n");
abort();
}
if (lenf == 1)
{
fmpz_mod_poly_zero(res);
return;
}
if (lenf == 2)
{
fmpz_mod_poly_t r, poly;
fmpz_mod_poly_init(tmp, &res->p);
fmpz_mod_poly_init(r, &res->p);
fmpz_mod_poly_init2(poly, &res->p, 2);
fmpz_mod_poly_set_coeff_ui (poly, 1, 1);
fmpz_mod_poly_divrem(tmp, r, poly, f);
fmpz_mod_poly_powmod_fmpz_binexp_preinv(res, r, e, f, finv);
fmpz_mod_poly_clear(tmp);
fmpz_mod_poly_clear(r);
fmpz_mod_poly_clear(poly);
return;
}
if (fmpz_abs_fits_ui(e))
{
ulong exp = fmpz_get_ui(e);
if (exp <= 2)
{
if (exp == UWORD(0))
{
fmpz_mod_poly_fit_length(res, 1);
fmpz_one(res->coeffs);
_fmpz_mod_poly_set_length(res, 1);
}
else if (exp == UWORD(1))
{
fmpz_mod_poly_t r;
fmpz_mod_poly_init2(r, &f->p, 2);
fmpz_mod_poly_set_coeff_ui(r, 1, 1);
fmpz_mod_poly_init(tmp, &f->p);
fmpz_mod_poly_divrem(tmp, res, r, f);
fmpz_mod_poly_clear(tmp);
fmpz_mod_poly_clear(r);
}
else
{
fmpz_mod_poly_init2(tmp, &f->p, 3);
fmpz_mod_poly_set_coeff_ui(tmp, 1, 1);
fmpz_mod_poly_mulmod(res, tmp, tmp, f);
fmpz_mod_poly_clear(tmp);
}
return;
}
}
if ((res == f) || (res == finv))
{
fmpz_mod_poly_init2(tmp, &f->p, trunc);
_fmpz_mod_poly_powmod_x_fmpz_preinv(tmp->coeffs, e, f->coeffs, lenf,
finv->coeffs, finv->length, &f->p);
fmpz_mod_poly_swap(res, tmp);
fmpz_mod_poly_clear(tmp);
}
else
{
fmpz_mod_poly_fit_length(res, trunc);
_fmpz_mod_poly_powmod_x_fmpz_preinv(res->coeffs, e, f->coeffs, lenf,
finv->coeffs, finv->length, &f->p);
}
_fmpz_mod_poly_set_length(res, trunc);
_fmpz_mod_poly_normalise(res);
}