pqc/external/flint-2.4.3/ulong_extras/euler_phi.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 Fredrik Johansson
******************************************************************************/
#include "flint.h"
#include "ulong_extras.h"
mp_limb_t n_euler_phi(mp_limb_t n)
{
int i;
mp_limb_t phi;
n_factor_t fac;
if (n < 2)
return n;
n_factor_init(&fac);
n_factor(&fac, n, 1);
phi = UWORD(1);
for (i = 0; i < fac.num; i++)
phi *= (fac.p[i]-1) * n_pow(fac.p[i], fac.exp[i]-1);
return phi;
}