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/*****************************************************************************
Copyright (c) 1994, 2016, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2019, 2020, MariaDB Corporation.
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.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA
*****************************************************************************/
/***************************************************************//**
@file ut/ut0rnd.cc
Random numbers and hashing
Created 5/11/1994 Heikki Tuuri
********************************************************************/
#include "ut0rnd.h"
/** Seed value of ut_rnd_gen() */
std::atomic<uint32_t> ut_rnd_current;
/** 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
/*@}*/
/***********************************************************//**
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 */
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);
}
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