~drizzle-trunk/drizzle/development

/*****************************************************************************

Copyright (c) 1994, 2009, Innobase Oy. All Rights Reserved.

This program 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; version 2 of the License.

This program 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

this program; if not, write to the Free Software Foundation, Inc., 59 Temple

Place, Suite 330, Boston, MA 02111-1307 USA

*****************************************************************************/

/***************************************************************//**

@file ut/ut0rnd.c

Random numbers and hashing

Created 5/11/1994 Heikki Tuuri

********************************************************************/

#include "ut0rnd.h"

#ifdef UNIV_NONINL

#include "ut0rnd.ic"

#endif

/** These random numbers are used in ut_find_prime */

/*@{*/

#define	UT_RANDOM_1	1.0412321

#define	UT_RANDOM_2	1.1131347

#define UT_RANDOM_3	1.0132677

/*@}*/

/** Seed value of ut_rnd_gen_ulint(). */

UNIV_INTERN ulint	ut_rnd_ulint_counter = 65654363;

/***********************************************************//**

Looks for a prime number slightly greater than the given argument.

The prime is chosen so that it is not near any power of 2.

@return	prime */

UNIV_INTERN

ulint

ut_find_prime(

/*==========*/

	ulint	n)	/*!< in: positive number > 100 */

{

	ulint	pow2;

	ulint	i;

	n += 100;

	pow2 = 1;

	while (pow2 * 2 < n) {

		pow2 = 2 * pow2;

	}

	if ((double)n < 1.05 * (double)pow2) {

		n = (ulint) ((double)n * UT_RANDOM_1);

	}

	pow2 = 2 * pow2;

	if ((double)n > 0.95 * (double)pow2) {

		n = (ulint) ((double)n * UT_RANDOM_2);

	}

	if (n > pow2 - 20) {

		n += 30;

	}

	/* Now we have n far enough from powers of 2. To make

	n more random (especially, if it was not near

	a power of 2), we then multiply it by a random number. */

	n = (ulint) ((double)n * UT_RANDOM_3);

	for (;; n++) {

		i = 2;

		while (i * i <= n) {

			if (n % i == 0) {

				goto next_n;

			}

			i++;

		}

		/* Found a prime */

		break;

next_n:		;

	}

	return(n);

}