ut0rnd.c
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上传日期:2022-05-23
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- /*******************************************************************
- Random numbers and hashing
- (c) 1994, 1995 Innobase Oy
- 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
- 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. */
- ulint
- ut_find_prime(
- /*==========*/
- /* out: 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);
- }