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tdutils/td/utils/Hash.h

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+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2017-2019 Telegram Systems LLP
+*/
+#pragma once
+
+#include "td/utils/common.h"
+
+#if TD_HAVE_ABSL
+#include <absl/hash/hash.h>
+#endif
+
+#include <utility>
+
+namespace td {
+// A simple wrapper for absl::flat_hash_map, std::unordered_map and probably some our implementaion of hash map in
+// the future
+
+// We will introduce out own Hashing utility like an absl one.
+class Hasher {
+ public:
+  Hasher() = default;
+  explicit Hasher(size_t init_value) : hash_(init_value) {
+  }
+  std::size_t finalize() const {
+    return hash_;
+  }
+
+  static Hasher combine(Hasher hasher, size_t value) {
+    hasher.hash_ ^= value;
+    return hasher;
+  }
+
+  template <class A, class B>
+  static Hasher combine(Hasher hasher, const std::pair<A, B> &value) {
+    hasher = AbslHashValue(std::move(hasher), value.first);
+    hasher = AbslHashValue(std::move(hasher), value.second);
+    return hasher;
+  }
+
+ private:
+  std::size_t hash_{0};
+};
+
+template <class IgnoreT>
+class TdHash {
+ public:
+  template <class T>
+  std::size_t operator()(const T &value) const noexcept {
+    return AbslHashValue(Hasher(), value).finalize();
+  }
+};
+
+#if TD_HAVE_ABSL
+template <class T>
+using AbslHash = absl::Hash<T>;
+#endif
+
+// default hash implementations
+template <class H, class T>
+decltype(H::combine(std::declval<H>(), std::declval<T>())) AbslHashValue(H hasher, const T &value) {
+  return H::combine(std::move(hasher), value);
+}
+
+#if TD_HAVE_ABSL
+template <class T>
+using Hash = AbslHash<T>;
+#else
+template <class T>
+using Hash = TdHash<T>;
+#endif
+
+}  // namespace td