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limitedmap.h
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// Copyright (c) 2012-2016 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_LIMITEDMAP_H
#define BITCOIN_LIMITEDMAP_H
#include <assert.h>
#include <map>
/** STL-like map container that only keeps the N elements with the highest value. */
template <typename K, typename V>
class limitedmap
{
public:
typedef K key_type;
typedef V mapped_type;
typedef std::pair<const key_type, mapped_type> value_type;
typedef typename std::map<K, V>::const_iterator const_iterator;
typedef typename std::map<K, V>::size_type size_type;
protected:
std::map<K, V> map;
typedef typename std::map<K, V>::iterator iterator;
std::multimap<V, iterator> rmap;
typedef typename std::multimap<V, iterator>::iterator rmap_iterator;
size_type nMaxSize;
public:
limitedmap(size_type nMaxSizeIn)
{
assert(nMaxSizeIn > 0);
nMaxSize = nMaxSizeIn;
}
const_iterator begin() const { return map.begin(); }
const_iterator end() const { return map.end(); }
size_type size() const { return map.size(); }
bool empty() const { return map.empty(); }
const_iterator find(const key_type& k) const { return map.find(k); }
size_type count(const key_type& k) const { return map.count(k); }
void insert(const value_type& x)
{
std::pair<iterator, bool> ret = map.insert(x);
if (ret.second) {
if (map.size() > nMaxSize) {
map.erase(rmap.begin()->second);
rmap.erase(rmap.begin());
}
rmap.insert(make_pair(x.second, ret.first));
}
}
void erase(const key_type& k)
{
iterator itTarget = map.find(k);
if (itTarget == map.end())
return;
std::pair<rmap_iterator, rmap_iterator> itPair = rmap.equal_range(itTarget->second);
for (rmap_iterator it = itPair.first; it != itPair.second; ++it)
if (it->second == itTarget) {
rmap.erase(it);
map.erase(itTarget);
return;
}
// Shouldn't ever get here
assert(0);
}
void update(const_iterator itIn, const mapped_type& v)
{
// Using map::erase() with empty range instead of map::find() to get a non-const iterator,
// since it is a constant time operation in C++11. For more details, see
// https://stackoverflow.com/questions/765148/how-to-remove-constness-of-const-iterator
iterator itTarget = map.erase(itIn, itIn);
if (itTarget == map.end())
return;
std::pair<rmap_iterator, rmap_iterator> itPair = rmap.equal_range(itTarget->second);
for (rmap_iterator it = itPair.first; it != itPair.second; ++it)
if (it->second == itTarget) {
rmap.erase(it);
itTarget->second = v;
rmap.insert(make_pair(v, itTarget));
return;
}
// Shouldn't ever get here
assert(0);
}
size_type max_size() const { return nMaxSize; }
size_type max_size(size_type s)
{
assert(s > 0);
while (map.size() > s) {
map.erase(rmap.begin()->second);
rmap.erase(rmap.begin());
}
nMaxSize = s;
return nMaxSize;
}
};
#endif // BITCOIN_LIMITEDMAP_H

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