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87 lines
2.6 KiB
C
87 lines
2.6 KiB
C
/*---------------------------------------------------------------------------*\
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========= |
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\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
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\\ / O peration |
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\\ / A nd | Copyright (C) 2011-2012 OpenFOAM Foundation
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\\/ M anipulation |
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-------------------------------------------------------------------------------
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License
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This file is part of OpenFOAM.
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OpenFOAM is free software: you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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OpenFOAM 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
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with OpenFOAM. If not, see <http://www.gnu.org/licenses/>.
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\*---------------------------------------------------------------------------*/
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#include "StaticHashTable.H"
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#include "uLabel.H"
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// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
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namespace Foam
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{
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defineTypeNameAndDebug(StaticHashTableCore, 0);
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}
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// Approximately labelMax/4
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static const Foam::label maxTableSize(1L << (sizeof(Foam::label)*8-3));
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// * * * * * * * * * * * * * * Member Functions * * * * * * * * * * * * * * //
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Foam::label Foam::StaticHashTableCore::canonicalSize(const label requested_size)
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{
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if (requested_size < 1)
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{
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return 0;
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}
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else if (requested_size >= maxTableSize)
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{
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return maxTableSize;
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}
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// Enforce power of two - makes for a very fast modulus.
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// Use unsigned for these calculations.
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//
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// - The lower limit (8) is somewhat arbitrary, but if the hash table
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// is too small, there will be many direct table collisions.
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// - The upper limit (approx. labelMax/4) must be a power of two,
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// need not be extremely large for hashing.
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uLabel powerOfTwo = 8u; // lower-limit
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const uLabel size = requested_size;
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if (size <= powerOfTwo)
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{
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return powerOfTwo;
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}
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else if (size & (size-1)) // <- Modulus of i^2
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{
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// Determine power-of-two. Brute-force is fast enough.
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while (powerOfTwo < size)
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{
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powerOfTwo <<= 1;
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}
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return powerOfTwo;
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}
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else
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{
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return size;
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}
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}
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// ************************************************************************* //
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