helpers.c

/* helpers.c -- helper functions for the gmp version of tests
 *
 * Copyright 2014 by Colin Benner <colin-software@yzhs.de>
 *
 * This file is part of frobenius-test.
 *
 * frobenius-test 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 3 of the License, or
 * (at your option) any later version.
 *
 * frobenius-test 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 frobenius-test.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdlib.h>
#include <sys/time.h>

#include "helpers.h"

gmp_randstate_t r_state;

mpz_t bb4c, base_x, base_1, tmp0, tmp1, tmp2;

/*
 * Seed random number generators.
 */
int init(void)
{
	long int seed = 123457;

	/* Uncomment the following lines to use a dynamic seed. */
	//struct timeval tv;
	//gettimeofday(&tv, NULL);
	//seed = tv.tv_usec;

	gmp_randinit_default(r_state);
	gmp_randseed_ui(r_state, seed);

	srand((unsigned int)seed);
	mpz_inits(bb4c, base_x, base_1, tmp0, tmp1, tmp2, NULL);

	return 0;
}

/*
 * Whatever is to be done before programme shutdown.
 */
int cleanup(void)
{
	mpz_clears(bb4c, base_x, base_1, tmp0, tmp1, tmp2, NULL);
	gmp_randclear(r_state);
	return 0;
}


/*
 * Calculate s, d such that n-1=2^s*d where d is odd.
 */
void split(uint64_t *s, mpz_t d, const mpz_t n)
{
	// Find the least significant bit that is set, except for the 2^0 bit.
	*s = mpz_scan1(n, 1);

	mpz_fdiv_q_2exp(d, n, *s);
}

/**
 * This function generates a random integer between 2 and n-2.
 */
void get_random(mpz_t result, const mpz_t n)
{
	mpz_t tmp;

	mpz_init(tmp);
	mpz_sub_ui(tmp, n, 3);

	// Generate a random number between 0 and tmp-1.  The results of
	// mpz_urandomm are uniformly distributed.
	mpz_urandomm(result, r_state, tmp);

	mpz_add_ui(result, result, 2);
	mpz_clear(tmp);
}

/*
 * Generate a random integer between low and high, both included.
 */
unsigned randint(const unsigned low, const unsigned high)
{
	// TODO make the distribution is uniform
	return low + (unsigned)rand() % (high - low + 1);
}