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-// Copyright 2018 The Abseil Authors.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//      https://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-//
-// -----------------------------------------------------------------------------
-// File: hash.h
-// -----------------------------------------------------------------------------
-//
-// This header file defines the Abseil `hash` library and the Abseil hashing
-// framework. This framework consists of the following:
-//
-//   * The `absl::Hash` functor, which is used to invoke the hasher within the
-//     Abseil hashing framework. `absl::Hash<T>` supports most basic types and
-//     a number of Abseil types out of the box.
-//   * `AbslHashValue`, an extension point that allows you to extend types to
-//     support Abseil hashing without requiring you to define a hashing
-//     algorithm.
-//   * `HashState`, a type-erased class which implements the manipulation of the
-//     hash state (H) itself, contains member functions `combine()` and
-//     `combine_contiguous()`, which you can use to contribute to an existing
-//     hash state when hashing your types.
-//
-// Unlike `std::hash` or other hashing frameworks, the Abseil hashing framework
-// provides most of its utility by abstracting away the hash algorithm (and its
-// implementation) entirely. Instead, a type invokes the Abseil hashing
-// framework by simply combining its state with the state of known, hashable
-// types. Hashing of that combined state is separately done by `absl::Hash`.
-//
-// One should assume that a hash algorithm is chosen randomly at the start of
-// each process.  E.g., `absl::Hash<int>{}(9)` in one process and
-// `absl::Hash<int>{}(9)` in another process are likely to differ.
-//
-// `absl::Hash` is intended to strongly mix input bits with a target of passing
-// an [Avalanche Test](https://en.wikipedia.org/wiki/Avalanche_effect).
-//
-// Example:
-//
-//   // Suppose we have a class `Circle` for which we want to add hashing:
-//   class Circle {
-//    public:
-//     ...
-//    private:
-//     std::pair<int, int> center_;
-//     int radius_;
-//   };
-//
-//   // To add hashing support to `Circle`, we simply need to add a free
-//   // (non-member) function `AbslHashValue()`, and return the combined hash
-//   // state of the existing hash state and the class state. You can add such a
-//   // free function using a friend declaration within the body of the class:
-//   class Circle {
-//    public:
-//     ...
-//     template <typename H>
-//     friend H AbslHashValue(H h, const Circle& c) {
-//       return H::combine(std::move(h), c.center_, c.radius_);
-//     }
-//     ...
-//   };
-//
-// For more information, see Adding Type Support to `absl::Hash` below.
-//
-#ifndef ABSL_HASH_HASH_H_
-#define ABSL_HASH_HASH_H_
-
-#include "absl/hash/internal/hash.h"
-
-namespace absl {
-ABSL_NAMESPACE_BEGIN
-
-// -----------------------------------------------------------------------------
-// `absl::Hash`
-// -----------------------------------------------------------------------------
-//
-// `absl::Hash<T>` is a convenient general-purpose hash functor for any type `T`
-// satisfying any of the following conditions (in order):
-//
-//  * T is an arithmetic or pointer type
-//  * T defines an overload for `AbslHashValue(H, const T&)` for an arbitrary
-//    hash state `H`.
-//  - T defines a specialization of `std::hash<T>`
-//
-// `absl::Hash` intrinsically supports the following types:
-//
-//   * All integral types (including bool)
-//   * All enum types
-//   * All floating-point types (although hashing them is discouraged)
-//   * All pointer types, including nullptr_t
-//   * std::pair<T1, T2>, if T1 and T2 are hashable
-//   * std::tuple<Ts...>, if all the Ts... are hashable
-//   * std::unique_ptr and std::shared_ptr
-//   * All string-like types including:
-//     * absl::Cord
-//     * std::string
-//     * std::string_view (as well as any instance of std::basic_string that
-//       uses char and std::char_traits)
-//  * All the standard sequence containers (provided the elements are hashable)
-//  * All the standard ordered associative containers (provided the elements are
-//    hashable)
-//  * absl types such as the following:
-//    * absl::string_view
-//    * absl::InlinedVector
-//    * absl::FixedArray
-//    * absl::uint128
-//    * absl::Time, absl::Duration, and absl::TimeZone
-//
-// Note: the list above is not meant to be exhaustive. Additional type support
-// may be added, in which case the above list will be updated.
-//
-// -----------------------------------------------------------------------------
-// absl::Hash Invocation Evaluation
-// -----------------------------------------------------------------------------
-//
-// When invoked, `absl::Hash<T>` searches for supplied hash functions in the
-// following order:
-//
-//   * Natively supported types out of the box (see above)
-//   * Types for which an `AbslHashValue()` overload is provided (such as
-//     user-defined types). See "Adding Type Support to `absl::Hash`" below.
-//   * Types which define a `std::hash<T>` specialization
-//
-// The fallback to legacy hash functions exists mainly for backwards
-// compatibility. If you have a choice, prefer defining an `AbslHashValue`
-// overload instead of specializing any legacy hash functors.
-//
-// -----------------------------------------------------------------------------
-// The Hash State Concept, and using `HashState` for Type Erasure
-// -----------------------------------------------------------------------------
-//
-// The `absl::Hash` framework relies on the Concept of a "hash state." Such a
-// hash state is used in several places:
-//
-// * Within existing implementations of `absl::Hash<T>` to store the hashed
-//   state of an object. Note that it is up to the implementation how it stores
-//   such state. A hash table, for example, may mix the state to produce an
-//   integer value; a testing framework may simply hold a vector of that state.
-// * Within implementations of `AbslHashValue()` used to extend user-defined
-//   types. (See "Adding Type Support to absl::Hash" below.)
-// * Inside a `HashState`, providing type erasure for the concept of a hash
-//   state, which you can use to extend the `absl::Hash` framework for types
-//   that are otherwise difficult to extend using `AbslHashValue()`. (See the
-//   `HashState` class below.)
-//
-// The "hash state" concept contains two member functions for mixing hash state:
-//
-// * `H::combine(state, values...)`
-//
-//   Combines an arbitrary number of values into a hash state, returning the
-//   updated state. Note that the existing hash state is move-only and must be
-//   passed by value.
-//
-//   Each of the value types T must be hashable by H.
-//
-//   NOTE:
-//
-//     state = H::combine(std::move(state), value1, value2, value3);
-//
-//   must be guaranteed to produce the same hash expansion as
-//
-//     state = H::combine(std::move(state), value1);
-//     state = H::combine(std::move(state), value2);
-//     state = H::combine(std::move(state), value3);
-//
-// * `H::combine_contiguous(state, data, size)`
-//
-//    Combines a contiguous array of `size` elements into a hash state,
-//    returning the updated state. Note that the existing hash state is
-//    move-only and must be passed by value.
-//
-//    NOTE:
-//
-//      state = H::combine_contiguous(std::move(state), data, size);
-//
-//    need NOT be guaranteed to produce the same hash expansion as a loop
-//    (it may perform internal optimizations). If you need this guarantee, use a
-//    loop instead.
-//
-// -----------------------------------------------------------------------------
-// Adding Type Support to `absl::Hash`
-// -----------------------------------------------------------------------------
-//
-// To add support for your user-defined type, add a proper `AbslHashValue()`
-// overload as a free (non-member) function. The overload will take an
-// existing hash state and should combine that state with state from the type.
-//
-// Example:
-//
-//   template <typename H>
-//   H AbslHashValue(H state, const MyType& v) {
-//     return H::combine(std::move(state), v.field1, ..., v.fieldN);
-//   }
-//
-// where `(field1, ..., fieldN)` are the members you would use on your
-// `operator==` to define equality.
-//
-// Notice that `AbslHashValue` is not a class member, but an ordinary function.
-// An `AbslHashValue` overload for a type should only be declared in the same
-// file and namespace as said type. The proper `AbslHashValue` implementation
-// for a given type will be discovered via ADL.
-//
-// Note: unlike `std::hash', `absl::Hash` should never be specialized. It must
-// only be extended by adding `AbslHashValue()` overloads.
-//
-template <typename T>
-using Hash = absl::hash_internal::Hash<T>;
-
-// HashState
-//
-// A type erased version of the hash state concept, for use in user-defined
-// `AbslHashValue` implementations that can't use templates (such as PImpl
-// classes, virtual functions, etc.). The type erasure adds overhead so it
-// should be avoided unless necessary.
-//
-// Note: This wrapper will only erase calls to:
-//     combine_contiguous(H, const unsigned char*, size_t)
-//
-// All other calls will be handled internally and will not invoke overloads
-// provided by the wrapped class.
-//
-// Users of this class should still define a template `AbslHashValue` function,
-// but can use `absl::HashState::Create(&state)` to erase the type of the hash
-// state and dispatch to their private hashing logic.
-//
-// This state can be used like any other hash state. In particular, you can call
-// `HashState::combine()` and `HashState::combine_contiguous()` on it.
-//
-// Example:
-//
-//   class Interface {
-//    public:
-//     template <typename H>
-//     friend H AbslHashValue(H state, const Interface& value) {
-//       state = H::combine(std::move(state), std::type_index(typeid(*this)));
-//       value.HashValue(absl::HashState::Create(&state));
-//       return state;
-//     }
-//    private:
-//     virtual void HashValue(absl::HashState state) const = 0;
-//   };
-//
-//   class Impl : Interface {
-//    private:
-//     void HashValue(absl::HashState state) const override {
-//       absl::HashState::combine(std::move(state), v1_, v2_);
-//     }
-//     int v1_;
-//     std::string v2_;
-//   };
-class HashState : public hash_internal::HashStateBase<HashState> {
- public:
-  // HashState::Create()
-  //
-  // Create a new `HashState` instance that wraps `state`. All calls to
-  // `combine()` and `combine_contiguous()` on the new instance will be
-  // redirected to the original `state` object. The `state` object must outlive
-  // the `HashState` instance.
-  template <typename T>
-  static HashState Create(T* state) {
-    HashState s;
-    s.Init(state);
-    return s;
-  }
-
-  HashState(const HashState&) = delete;
-  HashState& operator=(const HashState&) = delete;
-  HashState(HashState&&) = default;
-  HashState& operator=(HashState&&) = default;
-
-  // HashState::combine()
-  //
-  // Combines an arbitrary number of values into a hash state, returning the
-  // updated state.
-  using HashState::HashStateBase::combine;
-
-  // HashState::combine_contiguous()
-  //
-  // Combines a contiguous array of `size` elements into a hash state, returning
-  // the updated state.
-  static HashState combine_contiguous(HashState hash_state,
-                                      const unsigned char* first, size_t size) {
-    hash_state.combine_contiguous_(hash_state.state_, first, size);
-    return hash_state;
-  }
-  using HashState::HashStateBase::combine_contiguous;
-
- private:
-  HashState() = default;
-
-  template <typename T>
-  static void CombineContiguousImpl(void* p, const unsigned char* first,
-                                    size_t size) {
-    T& state = *static_cast<T*>(p);
-    state = T::combine_contiguous(std::move(state), first, size);
-  }
-
-  template <typename T>
-  void Init(T* state) {
-    state_ = state;
-    combine_contiguous_ = &CombineContiguousImpl<T>;
-  }
-
-  // Do not erase an already erased state.
-  void Init(HashState* state) {
-    state_ = state->state_;
-    combine_contiguous_ = state->combine_contiguous_;
-  }
-
-  void* state_;
-  void (*combine_contiguous_)(void*, const unsigned char*, size_t);
-};
-
-ABSL_NAMESPACE_END
-}  // namespace absl
-
-#endif  // ABSL_HASH_HASH_H_