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80 lines
2.0 KiB
C++
80 lines
2.0 KiB
C++
// lru-ish map.h
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/**
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* Copyright (C) 2008 10gen Inc.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License, version 3,
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include "../stdafx.h"
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#include "../util/goodies.h"
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namespace mongo {
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/* Your K object must define:
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int hash() - must always return > 0.
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operator==
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*/
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template <class K, class V, int MaxChain>
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class LRUishMap {
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public:
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LRUishMap(int _n) {
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n = nextPrime(_n);
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keys = new K[n];
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hashes = new int[n];
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for ( int i = 0; i < n; i++ ) hashes[i] = 0;
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}
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~LRUishMap() {
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delete[] keys;
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delete[] hashes;
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}
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int _find(const K& k, bool& found) {
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int h = k.hash();
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assert( h > 0 );
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int j = h % n;
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int first = j;
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for ( int i = 0; i < MaxChain; i++ ) {
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if ( hashes[j] == h ) {
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if ( keys[j] == k ) {
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found = true;
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return j;
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}
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}
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else if ( hashes[j] == 0 ) {
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found = false;
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return j;
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}
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}
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found = false;
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return first;
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}
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V* find(const K& k) {
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bool found;
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int j = _find(k, found);
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return found ? &values[j] : 0;
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}
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private:
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int n;
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K *keys;
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int *hashes;
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V *values;
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};
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} // namespace mongo
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