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