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/* hashtab.h
Simple, fixed size hash table. Darn simple.
Uses a contiguous block of memory, so you can put it in a memory mapped file very easily.
*/
/* 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 "../stdafx.h"
#include <map>
namespace mongo {
#pragma pack(1)
/* you should define:
int Key::hash() return > 0 always.
*/
template <
class Key,
class Type
>
class HashTable {
public:
const char *name;
struct Node {
int hash;
Key k;
Type value;
bool inUse() {
return hash != 0;
}
void setUnused() {
hash = 0;
}
} *nodes;
int n;
int maxChain;
int _find(const Key& k, bool& found) {
found = false;
int h = k.hash();
int i = h % n;
int start = i;
int chain = 0;
while ( 1 ) {
if ( !nodes[i].inUse() ) {
return i;
}
if ( nodes[i].hash == h && nodes[i].k == k ) {
found = true;
return i;
}
chain++;
i = (i+1) % n;
if ( i == start ) {
// shouldn't get here / defensive for infinite loops
out() << "error: hashtable " << name << " is full n:" << n << endl;
return -1;
}
if( chain >= maxChain ) {
out() << "error: hashtable " << name << " max chain n:" << n << endl;
return -1;
}
if ( chain == 200 )
out() << "warning: hashtable " << name << " long chain " << endl;
}
}
public:
/* buf must be all zeroes on initialization. */
HashTable(void *buf, int buflen, const char *_name) : name(_name) {
int m = sizeof(Node);
// out() << "hashtab init, buflen:" << buflen << " m:" << m << endl;
n = buflen / m;
if ( (n & 1) == 0 )
n--;
maxChain = (int) (n * 0.05);
nodes = (Node *) buf;
assert( sizeof(Node) == 628 );
//out() << "HashTable() " << _name << " sizeof(node):" << sizeof(Node) << " n:" << n << endl;
}
Type* get(const Key& k) {
bool found;
int i = _find(k, found);
if ( found )
return &nodes[i].value;
return 0;
}
void kill(const Key& k) {
bool found;
int i = _find(k, found);
if ( i >= 0 && found ) {
//TEMP nodes[i].k.kill();
nodes[i].setUnused();
}
}
/*
void drop(const Key& k) {
bool found;
int i = _find(k, found);
if ( i >= 0 && found ) {
nodes[i].setUnused();
}
}
*/
/** returns false if too full */
bool put(const Key& k, const Type& value) {
bool found;
int i = _find(k, found);
if ( i < 0 )
return false;
if ( !found ) {
nodes[i].k = k;
nodes[i].hash = k.hash();
}
else {
assert( nodes[i].hash == k.hash() );
}
nodes[i].value = value;
return true;
}
};
#pragma pack()
} // namespace mongo
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