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// lru-ish map.h
/* Copyright 2009 10gen Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include "../pch.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
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