release/src/router/mysql/storage/innodb_plugin/ut/ut0rnd.c

   1 /*****************************************************************************
   2
   3 Copyright (c) 1994, 2009, Innobase Oy. All Rights Reserved.
   4
   5 This program is free software; you can redistribute it and/or modify it under
   6 the terms of the GNU General Public License as published by the Free Software
   7 Foundation; version 2 of the License.
   8
   9 This program is distributed in the hope that it will be useful, but WITHOUT
  10 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  11 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
  12
  13 You should have received a copy of the GNU General Public License along with
  14 this program; if not, write to the Free Software Foundation, Inc.,
  15 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  16
  17 *****************************************************************************/
  18
  19 /***************************************************************//**
  20 @file ut/ut0rnd.c
  21 Random numbers and hashing
  22
  23 Created 5/11/1994 Heikki Tuuri
  24 ********************************************************************/
  25
  26 #include "ut0rnd.h"
  27
  28 #ifdef UNIV_NONINL
  29 #include "ut0rnd.ic"
  30 #endif
  31
  32 /** These random numbers are used in ut_find_prime */
  33 /*@{*/
  34 #define UT_RANDOM_1     1.0412321
  35 #define UT_RANDOM_2     1.1131347
  36 #define UT_RANDOM_3     1.0132677
  37 /*@}*/
  38
  39 /** Seed value of ut_rnd_gen_ulint(). */
  40 UNIV_INTERN ulint       ut_rnd_ulint_counter = 65654363;
  41
  42 /***********************************************************//**
  43 Looks for a prime number slightly greater than the given argument.
  44 The prime is chosen so that it is not near any power of 2.
  45 @return prime */
  46 UNIV_INTERN
  47 ulint
  48 ut_find_prime(
  49 /*==========*/
  50         ulint   n)      /*!< in: positive number > 100 */
  51 {
  52         ulint   pow2;
  53         ulint   i;
  54
  55         n += 100;
  56
  57         pow2 = 1;
  58         while (pow2 * 2 < n) {
  59                 pow2 = 2 * pow2;
  60         }
  61
  62         if ((double)n < 1.05 * (double)pow2) {
  63                 n = (ulint) ((double)n * UT_RANDOM_1);
  64         }
  65
  66         pow2 = 2 * pow2;
  67
  68         if ((double)n > 0.95 * (double)pow2) {
  69                 n = (ulint) ((double)n * UT_RANDOM_2);
  70         }
  71
  72         if (n > pow2 - 20) {
  73                 n += 30;
  74         }
  75
  76         /* Now we have n far enough from powers of 2. To make
  77         n more random (especially, if it was not near
  78         a power of 2), we then multiply it by a random number. */
  79
  80         n = (ulint) ((double)n * UT_RANDOM_3);
  81
  82         for (;; n++) {
  83                 i = 2;
  84                 while (i * i <= n) {
  85                         if (n % i == 0) {
  86                                 goto next_n;
  87                         }
  88                         i++;
  89                 }
  90
  91                 /* Found a prime */
  92                 break;
  93 next_n:         ;
  94         }
  95
  96         return(n);
  97 }