File indexing completed on 2021-12-21 13:28:00
0001 /** 0002 * Copyright (C) 2003 Maksim Orlovich <maksim.orlovich@kdemail.net> 0003 * 0004 * This program is free software; you can redistribute it and/or modify it under 0005 * the terms of the GNU General Public License as published by the Free Software 0006 * Foundation; either version 2 of the License, or (at your option) any later 0007 * version. 0008 * 0009 * This program is distributed in the hope that it will be useful, but WITHOUT ANY 0010 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A 0011 * PARTICULAR PURPOSE. See the GNU General Public License for more details. 0012 * 0013 * You should have received a copy of the GNU General Public License along with 0014 * this program. If not, see <http://www.gnu.org/licenses/>. 0015 */ 0016 #include "stringshare.h" 0017 0018 #include <QHash> 0019 0020 const int SIZE = 5003; 0021 0022 StringShare::Data* StringShare::s_data = 0; 0023 0024 /** 0025 * We store the strings in a simple direct-mapped (i.e. no collision handling, 0026 * just replace) hash, which contain strings or null objects. This costs only 0027 * 4 bytes per slot on 32-bit archs, so with the default constant size we only 0028 * really use 40K or so. 0029 * 0030 * The end result is that many strings end up pointing to the same underlying data 0031 * object, instead of each one having its own little copy. 0032 * 0033 * More importantly, the way the tryShare function is coded ensures that 0034 * most-recently inserted text stays in the cache, which gives a better chance 0035 * of continuing to share data. (Even if something old ("foo") that was shared 0036 * gets kicked out, all the other "foo"s will still be sharing each other's 0037 * data. 0038 */ 0039 0040 struct StringShare::Data 0041 { 0042 QString qstringHash [SIZE]; 0043 }; 0044 0045 StringShare::Data* StringShare::data() 0046 { 0047 if (!s_data) 0048 s_data = new Data; 0049 return s_data; 0050 } 0051 0052 QString StringShare::tryShare(const QString& in) 0053 { 0054 uint index = qHash(in) % SIZE; 0055 0056 Data* dat = data(); 0057 if (dat->qstringHash[index] == in) //Match 0058 return dat->qstringHash[index]; 0059 else 0060 { 0061 //Else replace whatever was there before 0062 dat->qstringHash[index] = in; 0063 return in; 0064 } 0065 } 0066 0067 // vim: set et sw=4 tw=0 sta: