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https://github.com/Open-Cascade-SAS/OCCT.git
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dpasukhi
1b4bb62150
Refactor TCollection to use NCollection_Primes and remove obsolete TCollection.cxx New prime declaration now will be more clear to use.
48 lines
2.2 KiB
C++
48 lines
2.2 KiB
C++
// Copyright (c) 2024 OPEN CASCADE SAS
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//
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// This file is part of Open CASCADE Technology software library.
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//
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// This library is free software; you can redistribute it and/or modify it under
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// the terms of the GNU Lesser General Public License version 2.1 as published
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// by the Free Software Foundation, with special exception defined in the file
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// OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
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// distribution for complete text of the license and disclaimer of any warranty.
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//
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// Alternatively, this file may be used under the terms of Open CASCADE
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// commercial license or contractual agreement.
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#include <NCollection_Primes.hxx>
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#include <Standard_OutOfRange.hxx>
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#include <algorithm>
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#include <array>
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namespace
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{
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// The array of prime numbers used as consecutive steps for
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// size of array of buckets in the map.
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// The prime numbers are used for array size with the hope that this will
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// lead to less probability of having the same hash codes for
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// different map items (note that all hash codes are modulo that size).
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// The value of each next step is chosen to be ~2 times greater than previous.
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// Though this could be thought as too much, actually the amount of
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// memory overhead in that case is only ~15% as compared with total size of
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// all auxiliary data structures (each map node takes ~24 bytes),
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// and this proves to pay off in performance (see OCC13189).
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constexpr std::array<int, 24> THE_PRIME_VECTOR = {101, 1009, 2003, 5003, 10007, 20011,
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37003, 57037, 65003, 100019, 209953, 472393,
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995329, 2359297, 4478977, 9437185, 17915905, 35831809,
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71663617, 150994945, 301989889, 573308929, 1019215873, 2038431745};
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}
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int NCollection_Primes::NextPrimeForMap(const int theN)
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{
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auto aResult = std::lower_bound(THE_PRIME_VECTOR.begin(), THE_PRIME_VECTOR.end(), theN + 1);
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if (aResult == THE_PRIME_VECTOR.end())
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{
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throw Standard_OutOfRange("NCollection_Primes::NextPrimeForMap() - requested too big size");
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}
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return *aResult;
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}
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