68 lines
1.9 KiB
C
68 lines
1.9 KiB
C
|
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved. This
|
||
|
|
// source code is licensed under the BSD-style license found in the LICENSE
|
||
|
|
// file in the root directory of this source tree. An additional grant of
|
||
|
|
// patent rights can be found in the PATENTS file in the same directory.
|
||
|
|
//
|
||
|
|
|
||
|
|
#pragma once
|
||
|
|
|
||
|
|
#include <algorithm>
|
||
|
|
#include <array>
|
||
|
|
#include <utility>
|
||
|
|
|
||
|
|
#include "util/autovector.h"
|
||
|
|
|
||
|
|
namespace rocksdb {
|
||
|
|
|
||
|
|
// 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, 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
|