pqc/external/flint-2.4.3/ulong_extras/prime_pi.c

67 lines
2.2 KiB
C
Raw Normal View History

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 <gmp.h>
#include "flint.h"
#include "ulong_extras.h"
const unsigned char FLINT_PRIME_PI_ODD_LOOKUP[] =
{
0,2,3,4,4,5,6,6,7,8,8,9,9,9,10,11,11,11,12,12,13,14,14,15,15,15,16,16,16,17,
18,18,18,19,19,20,21,21,21,22,22,23,23,23,24,24,24,24,25,25,26,27,27,28,29,
29,30,30,30,30,30,30,30,31,31,32,32,32,33,34,34,34,34,34,35,36,36,36,37,37,
37,38,38,39,39,39,40,40,40,41,42,42,42,42,42,43,44,44,45,46,46,46,46,46,46,
47,47,47,47,47,47,48,48,49,50,50,51,51,51,52,53,53,53,53,53,54,54,54,55,55,
55,56,56,56,57,58,58,58,59,59,60,61,61,61,61,61,62,62,62,62,62,62,62,63,63
};
ulong n_prime_pi(mp_limb_t n)
{
ulong low, mid, high;
const mp_limb_t * primes;
if (n < FLINT_PRIME_PI_ODD_LOOKUP_CUTOFF)
{
if (n < 3)
return (n == 2);
return FLINT_PRIME_PI_ODD_LOOKUP[(n-1)/2];
}
n_prime_pi_bounds(&low, &high, n);
primes = n_primes_arr_readonly(high + 1);
while (low < high)
{
mid = (low + high) / 2;
if (n < primes[mid-1])
high = mid;
else
low = mid + 1;
}
return low-1;
}