95 lines
2.5 KiB
C++
95 lines
2.5 KiB
C++
/*****************************************************************************
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Copyright (c) 1994, 2018, Oracle and/or its affiliates. All Rights Reserved.
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This program is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License, version 2.0, as published by the
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Free Software Foundation.
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This program is also distributed with certain software (including but not
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limited to OpenSSL) that is licensed under separate terms, as designated in a
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particular file or component or in included license documentation. The authors
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of MySQL hereby grant you an additional permission to link the program and
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your derivative works with the separately licensed software that they have
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included with MySQL.
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This program is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License, version 2.0,
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for more details.
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You should have received a copy of the GNU General Public License along with
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this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*****************************************************************************/
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/** @file ut/ut0rnd.cc
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Random numbers and hashing
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Created 5/11/1994 Heikki Tuuri
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********************************************************************/
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#include "ut0rnd.h"
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/** These random numbers are used in ut_find_prime */
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/*@{*/
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#define UT_RANDOM_1 1.0412321
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#define UT_RANDOM_2 1.1131347
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#define UT_RANDOM_3 1.0132677
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/*@}*/
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thread_local ulint ut_rnd_ulint_counter = 0;
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/** Looks for a prime number slightly greater than the given argument.
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The prime is chosen so that it is not near any power of 2.
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@return prime */
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ulint ut_find_prime(ulint n) /*!< in: positive number > 100 */
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{
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ulint pow2;
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ulint i;
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n += 100;
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pow2 = 1;
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while (pow2 * 2 < n) {
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pow2 = 2 * pow2;
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}
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if ((double)n < 1.05 * (double)pow2) {
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n = (ulint)((double)n * UT_RANDOM_1);
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}
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pow2 = 2 * pow2;
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if ((double)n > 0.95 * (double)pow2) {
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n = (ulint)((double)n * UT_RANDOM_2);
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}
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if (n > pow2 - 20) {
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n += 30;
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}
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/* Now we have n far enough from powers of 2. To make
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n more random (especially, if it was not near
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a power of 2), we then multiply it by a random number. */
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n = (ulint)((double)n * UT_RANDOM_3);
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for (;; n++) {
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i = 2;
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while (i * i <= n) {
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if (n % i == 0) {
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goto next_n;
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}
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i++;
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}
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/* Found a prime */
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break;
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next_n:;
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}
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return (n);
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}
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