/******************************************************************* 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); }