pqc/external/flint-2.4.3/ulong_extras/primitive_root_prime.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) 2013 Mike Hansen
******************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include "flint.h"
#include "ulong_extras.h"
mp_limb_t n_primitive_root_prime_prefactor(mp_limb_t p, n_factor_t * factors)
{
slong i;
int found;
mp_limb_t result, a, pm1;
double pinv;
if (p == 2)
{
return 1;
}
pm1 = p - 1;
pinv = n_precompute_inverse(p);
for (a = 2; a < p; a++)
{
found = 1;
for (i = 0; i < factors->num; i++)
{
result = n_powmod_precomp(a, pm1 / factors->p[i], p, pinv);
if (result == 1)
{
found = 0;
break;
}
}
if (found)
{
return a;
}
}
flint_printf("Exception (n_primitive_root_prime_prefactor). root not found.\n");
abort();
}
mp_limb_t n_primitive_root_prime(mp_limb_t p)
{
mp_limb_t a;
n_factor_t factors;
n_factor_init(&factors);
n_factor(&factors, p - 1, 1);
a = n_primitive_root_prime_prefactor(p, &factors);
return a;
}