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// lru-ish map.h
/* Copyright 2009 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
*/
#pragma once
#include "mongo/pch.h"
#include "mongo/util/goodies.h"
namespace mongo {
/* Your K object must define:
int hash() - must always return > 0.
operator==
*/
template <class K, class V, int MaxChain>
class LRUishMap {
public:
LRUishMap(int _n) {
n = nextPrime(_n);
keys = new K[n];
hashes = new int[n];
for ( int i = 0; i < n; i++ ) hashes[i] = 0;
}
~LRUishMap() {
delete[] keys;
delete[] hashes;
}
int _find(const K& k, bool& found) {
int h = k.hash();
verify( h > 0 );
int j = h % n;
int first = j;
for ( int i = 0; i < MaxChain; i++ ) {
if ( hashes[j] == h ) {
if ( keys[j] == k ) {
found = true;
return j;
}
}
else if ( hashes[j] == 0 ) {
found = false;
return j;
}
}
found = false;
return first;
}
V* find(const K& k) {
bool found;
int j = _find(k, found);
return found ? &values[j] : 0;
}
private:
int n;
K *keys;
int *hashes;
V *values;
};
} // namespace mongo
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