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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
#pragma once
#include <algorithm>
#include <array>
#include <utility>
#include "util/autovector.h"
namespace ROCKSDB_NAMESPACE {
// This is similar to std::unordered_map, except that it tries to avoid
// allocating or deallocating memory as much as possible. With
// std::unordered_map, an allocation/deallocation is made for every insertion
// or deletion because of the requirement that iterators remain valid even
// with insertions or deletions. This means that the hash chains will be
// implemented as linked lists.
//
// This implementation uses autovector as hash chains insteads.
//
template <typename K, typename V, size_t size = 128>
class HashMap {
std::array<autovector<std::pair<K, V>, 1>, size> table_;
public:
bool Contains(K key) {
auto& bucket = table_[key % size];
auto it = std::find_if(
bucket.begin(), bucket.end(),
[key](const std::pair<K, V>& p) { return p.first == key; });
return it != bucket.end();
}
void Insert(K key, const V& value) {
auto& bucket = table_[key % size];
bucket.push_back({key, value});
}
void Delete(K key) {
auto& bucket = table_[key % size];
auto it = std::find_if(
bucket.begin(), bucket.end(),
[key](const std::pair<K, V>& p) { return p.first == key; });
if (it != bucket.end()) {
auto last = bucket.end() - 1;
if (it != last) {
*it = *last;
}
bucket.pop_back();
}
}
V& Get(K key) {
auto& bucket = table_[key % size];
auto it = std::find_if(
bucket.begin(), bucket.end(),
[key](const std::pair<K, V>& p) { return p.first == key; });
return it->second;
}
};
} // namespace ROCKSDB_NAMESPACE
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