bignum-random-prime.c

/* bignum-random-prime.c

   Generation of random provable primes.

   Copyright (C) 2010, 2013 Niels Möller

   This file is part of GNU Nettle.

   GNU Nettle is free software: you can redistribute it and/or
   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at your
       option) any later version.

   or

     * 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.

   or both in parallel, as here.

   GNU Nettle 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 copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see http://www.gnu.org/licenses/.
*/

#if HAVE_CONFIG_H
# include "config.h"
#endif

#ifndef RANDOM_PRIME_VERBOSE
#define RANDOM_PRIME_VERBOSE 0
#endif

#include <assert.h>
#include <stdlib.h>

#if RANDOM_PRIME_VERBOSE
#include <stdio.h>
#define VERBOSE(x) (fputs((x), stderr))
#else
#define VERBOSE(x)
#endif

#include "bignum.h"
#include "hogweed-internal.h"
#include "macros.h"

/* Use a table of p_2 = 3 to p_{172} = 1021, used for sieving numbers
   of up to 20 bits. */

#define NPRIMES 171
#define TRIAL_DIV_BITS 20
#define TRIAL_DIV_MASK ((1 << TRIAL_DIV_BITS) - 1)

/* A 20-bit number x is divisible by p iff

     ((x * inverse) & TRIAL_DIV_MASK) <= limit
*/
struct trial_div_info {
  uint32_t inverse; /* p^{-1} (mod 2^20) */
  uint32_t limit;   /* floor( (2^20 - 1) / p) */
};