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df3855a471
ut_hash_ulint(): Remove. The exclusive OR before a modulus operation does not serve any useful purpose; it is only obfuscating code and wasting some CPU cycles. Reviewed by: Debarun Banerjee
116 lines
3.3 KiB
C++
116 lines
3.3 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, 2021, 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 std::atomic<uint32_t> 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= ut_rnd_current.load(std::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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ut_rnd_current.store(rnd, std::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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# if SIZEOF_SIZE_T < 8
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inline size_t ut_fold_ull(uint64_t d) noexcept
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{
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return size_t(d) * 31 + size_t(d >> (SIZEOF_SIZE_T * CHAR_BIT));
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}
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# else
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# define ut_fold_ull(d) d
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# endif
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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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