pqc/external/flint-2.4.3/ulong_extras/is_oddprime_binary.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 Thomas Boothby
Copyright (C) 2009 William Hart
Copyright (C) 2010 Fredrik Johansson
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "ulong_extras.h"
int n_is_oddprime_binary(mp_limb_t n)
{
ulong diff, prime_lo, prime_hi;
const mp_limb_t * primes;
n_prime_pi_bounds(&prime_lo, &prime_hi, n);
primes = n_primes_arr_readonly(prime_hi + 1);
if (n == primes[prime_hi]) return 1;
if (n > primes[prime_hi]) return 0;
diff = (prime_hi - prime_lo + 1) / 2;
while (1)
{
ulong diff2;
if (primes[prime_lo + diff] <= n) prime_lo += diff;
if (diff <= UWORD(1)) break;
diff = (diff + 1)/2;
diff2 = (prime_hi - prime_lo + 1)/2;
if (diff > diff2) diff = diff2;
}
return (n == primes[prime_lo]);
}