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b1f2d3a8c8
We should not need anywhere near 32 bits of entropy, so we might just limit ourselves to a 32-bit random number generator. Also, it might be cheaper to use exclusive-or, bit shifting and conditional jumps, instead of multiplication and addition. We use relaxed atomic operations on the global random number generator state in order in an attempt to silence any warnings about race conditions. There is an obvious race condition between the load and store in ut_rnd_gen(), but we do not think that it matters much that the state of the random number generator could 'stutter'. This change seems makes the 'uncompress_ops' nondeterministic in innodb_zip.cmp_per_index after the restart. It looks like there is an inherent race condition in the test, because the table could be opened for InnoDB statistics recalculation already before innodb_cmp_per_index_enabled was set. We might end up having uncompress_ops anywhere between 0 and 9, or perhaps even more. Let us remove that part of the test.
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.ic"
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#endif
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