Creation of LTS branch "lts_2018_12_18"

  - 44b0fafc62d9b8f192e8180cbe9c4b806b339d57 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 926bfeb9fff223429c12224b7514243886323e8d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 13327debebc5c2d1d4991b69fe50450e340e50e4 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 3088e76c597e068479e82508b1770a7ad0c806b6 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f6ae816808cd913e0e2b3e2af14f328fa1071af0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a06c4a1d9093137b7217a5aaba8920d62e835dc0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 7b46e1d31a6b08b1c6da2a13e7b151a20446fa07 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 070f6e47b33a2909d039e620c873204f78809492 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 7990fd459e9339467814ddb95000c87cb1e4d945 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f95179062eb65ce40895cc76f1398cce25394369 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - cc8dcd307b76a575d2e3e0958a4fe4c7193c2f68 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a705aa78dc76fc5c79d501e61dcc077eca68a8a4 Merge pull request #194 from Mizux/windows by Xiaoyi Zhang <zhangxy988@gmail.com>
  - a4c3ffff11eec0ee45742f915c255e9f870b7e0f Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 01174578651b73021d9b8c3820f6fea707dacdf0 Merge pull request #201 from ccawley2011/fix-byteswap by Matt Calabrese <38107210+mattcalabrese-google@users.noreply.github.com>
  - f86f9413856b65afdd61fea938d684b8ab73115a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 94c298e2a0ae409e283cab96c954a685bd865a70 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 0884a6a04e4497d11b1b398cc0e422b118bf977a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - c16d5557cd05119b5b7b1318ef778ebe3195b4a1 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 45221ccc4ed643e4209b0cc5798e97203f108fa8 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 2019e17a520575ab365b2b5134d71068182c70b8 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5b70a8910b2e6fb0ce5193a41873139a126d2f7f Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a00bdd176d66ef0b417d9576052a19091fbdf891 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f340f773edab951656b19b6f1a77c964a78ec4c2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 445998d7ac4e5d3c50411d377e3b50e960d2d6c2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - e821380d69a549dc64900693942789d21aa4df5e Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f21d187b80e3b7f08fb279775ea9c8b48c636030 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5441bbe1db5d0f2ca24b5b60166367b0966790af Fix code snippet in comment (#174) by Loo Rong Jie <loorongjie@gmail.com>
  - 5aae0cffae8ffaacab965756169b34e511b353df Fix CMake build (#173) by Stephan Dollberg <stephan.dollberg@gmail.com>
  - 48cd2c3f351ff188bc85684b84a91b6e6d17d896 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - e291c279e458761e77a69b09b129d3d1e81f1e80 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - e01d95528ea2137a4a27a88d1f57c6cb260aafed Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 8ff1374008259719b54a8cb128ef951c02da164c Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 02451914b9ad5320f81f56a89f3eef1f8683227c Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 921fd5cf02ec0d665439a790148d59faa7d4a72c Merge pull request #166 from rongjiecomputer/cmake-test by Gennadiy Civil <gennadiycivil@users.noreply.github.com>
  - fb462224c058487763f263b7995d70efd0242c17 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - c075ad321696fa5072e097f0a51e4fe76a6fe13e Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 0f4bc966754ec6cd28d5f03467d56f1efdc598e3 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 6c7e5ffc43decd92f7bdfc510ad8a245a20b6dea Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - d6df769173bf0263489f98874b93034db0e479a2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 28080f5f050c9530aa9f2b39c60d8217038d64ff Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 9c987f429bba32fb4446280fd3b91e2472d71d4d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 5e7d459eeca7bc53deab0ee9634601386b53d7c0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - bed5bd6e185c7e0311f3a1f2dab4c96083dac636 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - fefc83638fb69395d259ed245699310610429064 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - d8cfe9f2a77fbee02c09642491e62a3f3677e0f6 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - ad5c960b2eb914881d1ceba0e996a0a8f3f6ca59 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 86f0fe93ad9d6d033a319476736a3256369c1f75 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f0f15c2778b0e4959244dd25e63f445a455870f5 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 29ff6d4860070bf8fcbd39c8805d0c32d56628a3 Removed "warning treated as error" flag from MSVC (#153) by vocaviking <vocaviking@users.noreply.github.com>
  - 083d04dd4a62ebbf037079b06e49b323c5e1192a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - bea85b52733022294eef108a2e42d77b616ddca2 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 8f96be6ca60d967bd4b37f93d0a03bcff4145200 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 92e07e5590752d6b8e67f7f2f86c6286561e8cea Merge pull request #152 from clnperez/fix-multi-defines-p... by Derek Mauro <761129+derekmauro@users.noreply.github.com>
  - 2125e6444a9de9e41f21ecdc674dd7d8759c149d Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 9acad869d21731f5bc50430a33fe61cc0ffcbb0b Merge pull request #150 from OlafvdSpek/patch-2 by Jonathan Cohen <cohenjon@google.com>
  - c2e00d341913bf03b4597ade5b056042e23e8c58 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 9e060686d1c325f34f9806b45fe77bafeed00aee Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 7aa411ceafc1272a28579cca739a97a2fb79055a Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 2c5af55ed34850d8b7dd46177c8ca53fdfda920e Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 44aa275286baf97fc13529aca547a88b180beb08 Merge pull request #143 from rongjiecomputer/kernel by Xiaoyi Zhang <zhangxy988@gmail.com>
  - 42f22a28401c952f1fc5942231c7fdac80811bf5 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - b973bc53ef366f0253b85eeed9a79b241884a843 Merge pull request #139 from siepkes/smartos-support by ahedberg <ahedberg@google.com>
  - e0def7473e52336f58759e11db4cd9467e5e0356 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - f826f1d489b61b64df1d94afbe5981841a82e5fa Merge pull request #138 from edbaunton/remove-deprecated-... by ahedberg <ahedberg@google.com>
  - 7b50a4a94b0c7df68b3a854c850b551aaef0a8b4 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - a5030ca5125b9d557ecfeea8acc8b1a8e49f6d27 Merge pull request #144 from rongjiecomputer/winsock2 by Xiaoyi Zhang <zhangxy988@gmail.com>
  - 02687955b7ca8fc02ada9b14bc247deeb108d341 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 8f612ebb152fb7e05643a2bcf78cb89a8c0641ad Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 134496a31d8b324f762de3bee9a002658c984456 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - ba8d6cf07766263723e86736f20a51c1c9c67b19 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - be1e84b988fceabcea4fc9e93f899539f0c81901 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 16ac2ec2e38cdf47f9330a312e319d57da659c10 Merge pull request #134 from rongjiecomputer/cmake by Alex Strelnikov <strel@google.com>
  - 7efd8dc0f1075356e9c7caa950afd1ecf854e8b9 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 87a4c07856e7dc69958019d47b2f02ae47746ec0 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>
  - 4491d606df34c44efda47b6d17b605262f17e182 Export of internal Abseil changes. by Abseil Team <absl-team@google.com>

GitOrigin-RevId: 44b0fafc62d9b8f192e8180cbe9c4b806b339d57
Change-Id: I2c427b5b41b2d34101922048b00f3d9dafcb498d

1 files changed, 314 insertions, 0 deletions

diff --git a/absl/hash/hash.h b/absl/hash/hash.h
new file mode 100644
index 00000000..2c8982b8
--- /dev/null
+++ b/absl/hash/hash.h
@@ -0,0 +1,314 @@
+// 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
+//
+//      http://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`.
+//
+// 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 an ordinary
+//   // function `AbslHashValue()`, and return the combined hash state of the
+//   // existing hash state and the class state:
+//
+//     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 {
+inline namespace lts_2018_12_18 {
+
+// -----------------------------------------------------------------------------
+// `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 `HASH_NAMESPACE::hash<T>`
+//  - 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:
+//     * 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 `HASH_NAMESPACE::hash<T>` specialization (aka
+//     `__gnu_cxx::hash<T>` for gcc/Clang or `stdext::hash<T>` for MSVC)
+//   * 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_;
+//     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);
+};
+
+}  // inline namespace lts_2018_12_18
+}  // namespace absl
+#endif  // ABSL_HASH_HASH_H_