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author | Colin Cross <ccross@android.com> | 2022-04-13 03:15:00 +0000 |
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committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | 2022-04-13 03:15:00 +0000 |
commit | 6c9587948173932b64d97c288a947e43d2a2ac14 (patch) | |
tree | 2ce94d7f0804ccb77d1fa9b2a1bca00eecdff1e2 /third_party/abseil-cpp/absl/hash/hash.h | |
parent | f60eaea2240ba9e1c508e8e0c91d39ee9fc47be5 (diff) | |
parent | 43d8f56cdc20240b37c36bf417dd0d6999bce738 (diff) | |
download | webrtc-android13-qpr3-c-s11-release.tar.gz |
Merge changes I0ab600cd,I1e74c64a am: 798f3afdf6 am: 2f9c4b2c3b am: a9167328fc am: 7563023510 am: 43d8f56cdcandroid-13.0.0_r83android-13.0.0_r82android-13.0.0_r81android-13.0.0_r80android-13.0.0_r79android-13.0.0_r78android-13.0.0_r77android-13.0.0_r76android-13.0.0_r75android-13.0.0_r74android-13.0.0_r73android-13.0.0_r72android-13.0.0_r71android-13.0.0_r70android-13.0.0_r69android-13.0.0_r68android-13.0.0_r67android-13.0.0_r66android-13.0.0_r65android-13.0.0_r64android-13.0.0_r63android-13.0.0_r62android-13.0.0_r61android-13.0.0_r60android-13.0.0_r59android-13.0.0_r58android-13.0.0_r56android-13.0.0_r54android-13.0.0_r53android-13.0.0_r52android-13.0.0_r51android-13.0.0_r50android-13.0.0_r49android-13.0.0_r48android-13.0.0_r47android-13.0.0_r46android-13.0.0_r45android-13.0.0_r44android-13.0.0_r43android-13.0.0_r42android-13.0.0_r41android-13.0.0_r40android-13.0.0_r39android-13.0.0_r38android-13.0.0_r37android-13.0.0_r36android-13.0.0_r35android-13.0.0_r34android-13.0.0_r33android-13.0.0_r32android13-qpr3-s9-releaseandroid13-qpr3-s8-releaseandroid13-qpr3-s7-releaseandroid13-qpr3-s6-releaseandroid13-qpr3-s5-releaseandroid13-qpr3-s4-releaseandroid13-qpr3-s3-releaseandroid13-qpr3-s2-releaseandroid13-qpr3-s14-releaseandroid13-qpr3-s13-releaseandroid13-qpr3-s12-releaseandroid13-qpr3-s11-releaseandroid13-qpr3-s10-releaseandroid13-qpr3-s1-releaseandroid13-qpr3-releaseandroid13-qpr3-c-s8-releaseandroid13-qpr3-c-s7-releaseandroid13-qpr3-c-s6-releaseandroid13-qpr3-c-s5-releaseandroid13-qpr3-c-s4-releaseandroid13-qpr3-c-s3-releaseandroid13-qpr3-c-s2-releaseandroid13-qpr3-c-s12-releaseandroid13-qpr3-c-s11-releaseandroid13-qpr3-c-s10-releaseandroid13-qpr3-c-s1-releaseandroid13-qpr2-s9-releaseandroid13-qpr2-s8-releaseandroid13-qpr2-s7-releaseandroid13-qpr2-s6-releaseandroid13-qpr2-s5-releaseandroid13-qpr2-s3-releaseandroid13-qpr2-s2-releaseandroid13-qpr2-s12-releaseandroid13-qpr2-s11-releaseandroid13-qpr2-s10-releaseandroid13-qpr2-s1-releaseandroid13-qpr2-releaseandroid13-qpr2-b-s1-releaseandroid13-d4-s2-releaseandroid13-d4-s1-releaseandroid13-d4-release
Original change: https://android-review.googlesource.com/c/platform/external/webrtc/+/2062410
Change-Id: I1aa9f459b825711b800cc65782979943a9151ec7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
Diffstat (limited to 'third_party/abseil-cpp/absl/hash/hash.h')
-rw-r--r-- | third_party/abseil-cpp/absl/hash/hash.h | 33 |
1 files changed, 28 insertions, 5 deletions
diff --git a/third_party/abseil-cpp/absl/hash/hash.h b/third_party/abseil-cpp/absl/hash/hash.h index 23a65ea868..8282ea53c6 100644 --- a/third_party/abseil-cpp/absl/hash/hash.h +++ b/third_party/abseil-cpp/absl/hash/hash.h @@ -37,8 +37,11 @@ // 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. +// 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: // @@ -70,6 +73,8 @@ #ifndef ABSL_HASH_HASH_H_ #define ABSL_HASH_HASH_H_ +#include <tuple> + #include "absl/hash/internal/hash.h" namespace absl { @@ -85,7 +90,6 @@ ABSL_NAMESPACE_BEGIN // * 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: @@ -98,6 +102,7 @@ ABSL_NAMESPACE_BEGIN // * 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) @@ -124,8 +129,6 @@ ABSL_NAMESPACE_BEGIN // * 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 @@ -213,6 +216,26 @@ ABSL_NAMESPACE_BEGIN template <typename T> using Hash = absl::hash_internal::Hash<T>; +// HashOf +// +// absl::HashOf() is a helper that generates a hash from the values of its +// arguments. It dispatches to absl::Hash directly, as follows: +// * HashOf(t) == absl::Hash<T>{}(t) +// * HashOf(a, b, c) == HashOf(std::make_tuple(a, b, c)) +// +// HashOf(a1, a2, ...) == HashOf(b1, b2, ...) is guaranteed when +// * The argument lists have pairwise identical C++ types +// * a1 == b1 && a2 == b2 && ... +// +// The requirement that the arguments match in both type and value is critical. +// It means that `a == b` does not necessarily imply `HashOf(a) == HashOf(b)` if +// `a` and `b` have different types. For example, `HashOf(2) != HashOf(2.0)`. +template <int&... ExplicitArgumentBarrier, typename... Types> +size_t HashOf(const Types&... values) { + auto tuple = std::tie(values...); + return absl::Hash<decltype(tuple)>{}(tuple); +} + // HashState // // A type erased version of the hash state concept, for use in user-defined |