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/*****************************************************************************
Copyright (c) 1994, 2016, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2019, 2021, MariaDB Corporation.
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA
*****************************************************************************/
/******************************************************************//**
@file include/ut0rnd.h
Random numbers and hashing
Created 1/20/1994 Heikki Tuuri
***********************************************************************/
#ifndef ut0rnd_h
#define ut0rnd_h
#include "ut0byte.h"
#include <my_sys.h>
#ifndef UNIV_INNOCHECKSUM
/** Seed value of ut_rnd_gen() */
extern std::atomic<uint32_t> ut_rnd_current;
/** @return a pseudo-random 32-bit number */
inline uint32_t ut_rnd_gen()
{
/* This is a Galois linear-feedback shift register.
https://en.wikipedia.org/wiki/Linear-feedback_shift_register#Galois_LFSRs
The generating primitive Galois Field polynomial is the Castagnoli
polynomial that was made popular by CRC-32C:
x^32+x^28+x^27+x^26+x^25+x^23+x^22+x^20+
x^19+x^18+x^14+x^13+x^11+x^10+x^9+x^8+x^6+1 */
const uint32_t crc32c= 0x1edc6f41;
uint32_t rnd= ut_rnd_current.load(std::memory_order_relaxed);
if (UNIV_UNLIKELY(rnd == 0))
{
rnd= static_cast<uint32_t>(my_interval_timer());
if (!rnd) rnd= 1;
}
else
{
bool lsb= rnd & 1;
rnd>>= 1;
if (lsb)
rnd^= crc32c;
}
ut_rnd_current.store(rnd, std::memory_order_relaxed);
return rnd;
}
/** @return a random number between 0 and n-1, inclusive */
inline ulint ut_rnd_interval(ulint n)
{
return n > 1 ? static_cast<ulint>(ut_rnd_gen() % n) : 0;
}
/*******************************************************//**
The following function generates a hash value for a ulint integer
to a hash table of size table_size, which should be a prime or some
random number to work reliably.
@return hash value */
UNIV_INLINE
ulint
ut_hash_ulint(
/*==========*/
ulint key, /*!< in: value to be hashed */
ulint table_size); /*!< in: hash table size */
/*************************************************************//**
Folds a 64-bit integer.
@return folded value */
UNIV_INLINE
ulint
ut_fold_ull(
/*========*/
ib_uint64_t d) /*!< in: 64-bit integer */
MY_ATTRIBUTE((const));
/***********************************************************//**
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.
@return prime */
ulint
ut_find_prime(
/*==========*/
ulint n) /*!< in: positive number > 100 */
MY_ATTRIBUTE((const));
#endif /* !UNIV_INNOCHECKSUM */
/*************************************************************//**
Folds a pair of ulints.
@return folded value */
UNIV_INLINE
ulint
ut_fold_ulint_pair(
/*===============*/
ulint n1, /*!< in: ulint */
ulint n2) /*!< in: ulint */
MY_ATTRIBUTE((const));
/*************************************************************//**
Folds a binary string.
@return folded value */
UNIV_INLINE
ulint
ut_fold_binary(
/*===========*/
const byte* str, /*!< in: string of bytes */
ulint len) /*!< in: length */
MY_ATTRIBUTE((pure));
#include "ut0rnd.ic"
#endif
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