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67 lines
2 KiB
C++
67 lines
2 KiB
C++
/**
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* Copyright (C) 2003 Maksim Orlovich <maksim.orlovich@kdemail.net>
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*
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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; either version 2 of the License, or (at your option) any later
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* version.
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*
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* This program is distributed in the hope that it will be useful, but WITHOUT ANY
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* WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
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* PARTICULAR PURPOSE. See the GNU General Public License for more details.
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*
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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, see <http://www.gnu.org/licenses/>.
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*/
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#include "stringshare.h"
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#include <QHash>
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const int SIZE = 5003;
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StringShare::Data* StringShare::s_data = 0;
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/**
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* We store the strings in a simple direct-mapped (i.e. no collision handling,
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* just replace) hash, which contain strings or null objects. This costs only
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* 4 bytes per slot on 32-bit archs, so with the default constant size we only
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* really use 40K or so.
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*
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* The end result is that many strings end up pointing to the same underlying data
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* object, instead of each one having its own little copy.
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*
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* More importantly, the way the tryShare function is coded ensures that
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* most-recently inserted text stays in the cache, which gives a better chance
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* of continuing to share data. (Even if something old ("foo") that was shared
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* gets kicked out, all the other "foo"s will still be sharing each other's
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* data.
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*/
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struct StringShare::Data
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{
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QString qstringHash [SIZE];
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};
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StringShare::Data* StringShare::data()
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{
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if (!s_data)
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s_data = new Data;
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return s_data;
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}
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QString StringShare::tryShare(const QString& in)
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{
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uint index = qHash(in) % SIZE;
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Data* dat = data();
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if (dat->qstringHash[index] == in) //Match
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return dat->qstringHash[index];
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else
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{
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//Else replace whatever was there before
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dat->qstringHash[index] = in;
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return in;
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}
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}
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// vim: set et sw=4 tw=0 sta:
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