pqc/external/flint-2.4.3/fmpz/powm.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) 2009 William Hart
Copyright (C) 2011 Sebastian Pancratz
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "ulong_extras.h"
void fmpz_powm(fmpz_t f, const fmpz_t g, const fmpz_t e, const fmpz_t m)
{
if (fmpz_sgn(m) <= 0)
{
flint_printf("Exception (fmpz_powm). Modulus is less than 1.\n");
abort();
}
else if (!COEFF_IS_MPZ(*e)) /* e is small */
{
fmpz_powm_ui(f, g, *e, m);
}
else /* e is large */
{
if (!COEFF_IS_MPZ(*m)) /* m is small */
{
ulong g1 = fmpz_fdiv_ui(g, *m);
mpz_t g2, m2;
__mpz_struct *mpz_ptr;
flint_mpz_init_set_ui(g2, g1);
flint_mpz_init_set_ui(m2, *m);
mpz_ptr = _fmpz_promote(f);
mpz_powm(mpz_ptr, g2, COEFF_TO_PTR(*e), m2);
mpz_clear(g2);
mpz_clear(m2);
_fmpz_demote_val(f);
}
else /* m is large */
{
if (!COEFF_IS_MPZ(*g)) /* g is small */
{
mpz_t g2;
__mpz_struct *mpz_ptr;
flint_mpz_init_set_si(g2, *g);
mpz_ptr = _fmpz_promote(f);
mpz_powm(mpz_ptr, g2, COEFF_TO_PTR(*e), COEFF_TO_PTR(*m));
mpz_clear(g2);
_fmpz_demote_val(f);
}
else /* g is large */
{
__mpz_struct *mpz_ptr = _fmpz_promote(f);
mpz_powm(mpz_ptr,
COEFF_TO_PTR(*g), COEFF_TO_PTR(*e), COEFF_TO_PTR(*m));
_fmpz_demote_val(f);
}
}
}
}