74 lines
1.7 KiB
C++
74 lines
1.7 KiB
C++
//
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// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2019
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#pragma once
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#include "td/utils/common.h"
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#if TD_HAVE_ABSL
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#include <absl/hash/hash.h>
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#endif
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namespace td {
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// A simple wrapper for absl::flat_hash_map, std::unordered_map and probably some our implementaion of hash map in
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// the future
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// We will introduce out own Hashing utility like an absl one.
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class Hasher {
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public:
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Hasher() = default;
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explicit Hasher(size_t init_value) : hash_(init_value) {
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}
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std::size_t finalize() const {
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return hash_;
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}
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static Hasher combine(Hasher hasher, size_t value) {
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hasher.hash_ ^= value;
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return hasher;
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}
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template <class A, class B>
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static Hasher combine(Hasher hasher, const std::pair<A, B> &value) {
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hasher = AbslHashValue(std::move(hasher), value.first);
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hasher = AbslHashValue(std::move(hasher), value.second);
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return hasher;
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}
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private:
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std::size_t hash_{0};
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};
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template <class IgnoreT>
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class TdHash {
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public:
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template <class T>
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std::size_t operator()(const T &value) const noexcept {
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return AbslHashValue(Hasher(), value).finalize();
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}
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};
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#if TD_HAVE_ABSL
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template <class T>
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using AbslHash = absl::Hash<T>;
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#endif
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// default hash implementations
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template <class H, class T>
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decltype(H::combine(std::declval<H>(), std::declval<T>())) AbslHashValue(H hasher, const T &value) {
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return H::combine(std::move(hasher), value);
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}
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#if TD_HAVE_ABSL
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template <class T>
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using Hash = AbslHash<T>;
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#else
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template <class T>
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using Hash = TdHash<T>;
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#endif
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} // namespace td
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