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138 lines
4 KiB
C
138 lines
4 KiB
C
/*****************************************************************************
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Copyright (c) 1994, 2016, Oracle and/or its affiliates. All Rights Reserved.
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Copyright (c) 2019, MariaDB Corporation.
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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 as published by the Free Software
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Foundation; version 2 of the License.
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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 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 Street, Fifth Floor, Boston, MA 02110-1335 USA
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*****************************************************************************/
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/******************************************************************//**
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@file include/ut0rnd.h
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Random numbers and hashing
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Created 1/20/1994 Heikki Tuuri
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***********************************************************************/
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#ifndef ut0rnd_h
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#define ut0rnd_h
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#include "ut0byte.h"
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#include <my_sys.h>
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#ifndef UNIV_INNOCHECKSUM
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/** Seed value of ut_rnd_gen() */
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extern int32 ut_rnd_current;
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/** @return a pseudo-random 32-bit number */
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inline uint32_t ut_rnd_gen()
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{
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/* This is a Galois linear-feedback shift register.
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https://en.wikipedia.org/wiki/Linear-feedback_shift_register#Galois_LFSRs
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The generating primitive Galois Field polynomial is the Castagnoli
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polynomial that was made popular by CRC-32C:
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x^32+x^28+x^27+x^26+x^25+x^23+x^22+x^20+
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x^19+x^18+x^14+x^13+x^11+x^10+x^9+x^8+x^6+1 */
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const uint32_t crc32c= 0x1edc6f41;
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uint32_t rnd= my_atomic_load32_explicit(&ut_rnd_current,
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MY_MEMORY_ORDER_RELAXED);
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if (UNIV_UNLIKELY(rnd == 0))
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{
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rnd= static_cast<uint32_t>(my_interval_timer());
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if (!rnd) rnd= 1;
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}
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else
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{
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bool lsb= rnd & 1;
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rnd>>= 1;
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if (lsb)
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rnd^= crc32c;
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}
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my_atomic_store32_explicit(&ut_rnd_current, rnd, MY_MEMORY_ORDER_RELAXED);
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return rnd;
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}
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/** @return a random number between 0 and n-1, inclusive */
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inline ulint ut_rnd_interval(ulint n)
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{
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return n > 1 ? static_cast<ulint>(ut_rnd_gen() % n) : 0;
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}
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/*******************************************************//**
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The following function generates a hash value for a ulint integer
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to a hash table of size table_size, which should be a prime or some
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random number to work reliably.
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@return hash value */
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UNIV_INLINE
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ulint
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ut_hash_ulint(
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/*==========*/
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ulint key, /*!< in: value to be hashed */
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ulint table_size); /*!< in: hash table size */
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/*************************************************************//**
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Folds a 64-bit integer.
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@return folded value */
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UNIV_INLINE
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ulint
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ut_fold_ull(
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/*========*/
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ib_uint64_t d) /*!< in: 64-bit integer */
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MY_ATTRIBUTE((const));
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/*************************************************************//**
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Folds a character string ending in the null character.
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@return folded value */
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UNIV_INLINE
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ulint
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ut_fold_string(
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/*===========*/
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const char* str) /*!< in: null-terminated string */
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MY_ATTRIBUTE((warn_unused_result));
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/***********************************************************//**
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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
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ut_find_prime(
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/*==========*/
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ulint n) /*!< in: positive number > 100 */
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MY_ATTRIBUTE((const));
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#endif /* !UNIV_INNOCHECKSUM */
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/*************************************************************//**
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Folds a pair of ulints.
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@return folded value */
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UNIV_INLINE
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ulint
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ut_fold_ulint_pair(
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/*===============*/
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ulint n1, /*!< in: ulint */
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ulint n2) /*!< in: ulint */
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MY_ATTRIBUTE((const));
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/*************************************************************//**
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Folds a binary string.
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@return folded value */
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UNIV_INLINE
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ulint
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ut_fold_binary(
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/*===========*/
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const byte* str, /*!< in: string of bytes */
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ulint len) /*!< in: length */
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MY_ATTRIBUTE((pure));
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#include "ut0rnd.inl"
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#endif
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