mongodb/util/lruishmap.h

// lru-ish map.h

/**
*    Copyright (C) 2008 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/>.
*/

#pragma once

#include "../stdafx.h"
#include "../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();
        assert( 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