diff options
Diffstat (limited to 'src/third_party/abseil-cpp-master/abseil-cpp/absl/hash/hash.h')
| -rw-r--r-- | src/third_party/abseil-cpp-master/abseil-cpp/absl/hash/hash.h | 47 |
1 files changed, 30 insertions, 17 deletions
diff --git a/src/third_party/abseil-cpp-master/abseil-cpp/absl/hash/hash.h b/src/third_party/abseil-cpp-master/abseil-cpp/absl/hash/hash.h index 36c7c2b3b6d..5de132cac8a 100644 --- a/src/third_party/abseil-cpp-master/abseil-cpp/absl/hash/hash.h +++ b/src/third_party/abseil-cpp-master/abseil-cpp/absl/hash/hash.h @@ -4,7 +4,7 @@ // 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 +// 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, @@ -36,25 +36,37 @@ // 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 +// // 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: +// 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. // @@ -64,6 +76,7 @@ #include "absl/hash/internal/hash.h" namespace absl { +ABSL_NAMESPACE_BEGIN // ----------------------------------------------------------------------------- // `absl::Hash` @@ -75,7 +88,6 @@ namespace absl { // * 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: @@ -88,6 +100,7 @@ namespace absl { // * 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) @@ -114,8 +127,6 @@ namespace absl { // * 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 @@ -235,7 +246,7 @@ using Hash = absl::hash_internal::Hash<T>; // } // private: // virtual void HashValue(absl::HashState state) const = 0; -// }; +// }; // // class Impl : Interface { // private: @@ -243,7 +254,7 @@ using Hash = absl::hash_internal::Hash<T>; // absl::HashState::combine(std::move(state), v1_, v2_); // } // int v1_; -// string v2_; +// std::string v2_; // }; class HashState : public hash_internal::HashStateBase<HashState> { public: @@ -308,5 +319,7 @@ class HashState : public hash_internal::HashStateBase<HashState> { void (*combine_contiguous_)(void*, const unsigned char*, size_t); }; +ABSL_NAMESPACE_END } // namespace absl + #endif // ABSL_HASH_HASH_H_ |