diff options
Diffstat (limited to 'abseil-cpp/absl/hash/internal/hash.h')
| -rw-r--r-- | abseil-cpp/absl/hash/internal/hash.h | 476 |
1 files changed, 404 insertions, 72 deletions
diff --git a/abseil-cpp/absl/hash/internal/hash.h b/abseil-cpp/absl/hash/internal/hash.h index 9e608f7..ef3f366 100644 --- a/abseil-cpp/absl/hash/internal/hash.h +++ b/abseil-cpp/absl/hash/internal/hash.h @@ -21,7 +21,9 @@ #include <algorithm> #include <array> +#include <bitset> #include <cmath> +#include <cstddef> #include <cstring> #include <deque> #include <forward_list> @@ -35,22 +37,34 @@ #include <string> #include <tuple> #include <type_traits> +#include <unordered_map> +#include <unordered_set> #include <utility> #include <vector> -#include "absl/base/internal/endian.h" +#include "absl/base/config.h" +#include "absl/base/internal/unaligned_access.h" #include "absl/base/port.h" #include "absl/container/fixed_array.h" +#include "absl/hash/internal/city.h" +#include "absl/hash/internal/low_level_hash.h" #include "absl/meta/type_traits.h" +#include "absl/numeric/bits.h" #include "absl/numeric/int128.h" #include "absl/strings/string_view.h" #include "absl/types/optional.h" #include "absl/types/variant.h" #include "absl/utility/utility.h" -#include "absl/hash/internal/city.h" + +#ifdef ABSL_HAVE_STD_STRING_VIEW +#include <string_view> +#endif namespace absl { ABSL_NAMESPACE_BEGIN + +class HashState; + namespace hash_internal { // Internal detail: Large buffers are hashed in smaller chunks. This function @@ -112,24 +126,66 @@ class PiecewiseCombiner { size_t position_; }; +// is_hashable() +// +// Trait class which returns true if T is hashable by the absl::Hash framework. +// Used for the AbslHashValue implementations for composite types below. +template <typename T> +struct is_hashable; + // HashStateBase // -// A hash state object represents an intermediate state in the computation -// of an unspecified hash algorithm. `HashStateBase` provides a CRTP style -// base class for hash state implementations. Developers adding type support -// for `absl::Hash` should not rely on any parts of the state object other than -// the following member functions: +// An internal implementation detail that contains common implementation details +// for all of the "hash state objects" objects generated by Abseil. This is not +// a public API; users should not create classes that inherit from this. +// +// A hash state object is the template argument `H` passed to `AbslHashValue`. +// It represents an intermediate state in the computation of an unspecified hash +// algorithm. `HashStateBase` provides a CRTP style base class for hash state +// implementations. Developers adding type support for `absl::Hash` should not +// rely on any parts of the state object other than the following member +// functions: // // * HashStateBase::combine() // * HashStateBase::combine_contiguous() +// * HashStateBase::combine_unordered() // -// A derived hash state class of type `H` must provide a static member function +// A derived hash state class of type `H` must provide a public member function // with a signature similar to the following: // // `static H combine_contiguous(H state, const unsigned char*, size_t)`. // +// It must also provide a private template method named RunCombineUnordered. +// +// A "consumer" is a 1-arg functor returning void. Its argument is a reference +// to an inner hash state object, and it may be called multiple times. When +// called, the functor consumes the entropy from the provided state object, +// and resets that object to its empty state. +// +// A "combiner" is a stateless 2-arg functor returning void. Its arguments are +// an inner hash state object and an ElementStateConsumer functor. A combiner +// uses the provided inner hash state object to hash each element of the +// container, passing the inner hash state object to the consumer after hashing +// each element. +// +// Given these definitions, a derived hash state class of type H +// must provide a private template method with a signature similar to the +// following: +// +// `template <typename CombinerT>` +// `static H RunCombineUnordered(H outer_state, CombinerT combiner)` +// +// This function is responsible for constructing the inner state object and +// providing a consumer to the combiner. It uses side effects of the consumer +// and combiner to mix the state of each element in an order-independent manner, +// and uses this to return an updated value of `outer_state`. +// +// This inside-out approach generates efficient object code in the normal case, +// but allows us to use stack storage to implement the absl::HashState type +// erasure mechanism (avoiding heap allocations while hashing). +// // `HashStateBase` will provide a complete implementation for a hash state -// object in terms of this method. +// object in terms of these two methods. // // Example: // @@ -138,6 +194,10 @@ class PiecewiseCombiner { // static H combine_contiguous(H state, const unsigned char*, size_t); // using MyHashState::HashStateBase::combine; // using MyHashState::HashStateBase::combine_contiguous; +// using MyHashState::HashStateBase::combine_unordered; +// private: +// template <typename CombinerT> +// static H RunCombineUnordered(H state, CombinerT combiner); // }; template <typename H> class HashStateBase { @@ -178,7 +238,30 @@ class HashStateBase { template <typename T> static H combine_contiguous(H state, const T* data, size_t size); + template <typename I> + static H combine_unordered(H state, I begin, I end); + using AbslInternalPiecewiseCombiner = PiecewiseCombiner; + + template <typename T> + using is_hashable = absl::hash_internal::is_hashable<T>; + + private: + // Common implementation of the iteration step of a "combiner", as described + // above. + template <typename I> + struct CombineUnorderedCallback { + I begin; + I end; + + template <typename InnerH, typename ElementStateConsumer> + void operator()(InnerH inner_state, ElementStateConsumer cb) { + for (; begin != end; ++begin) { + inner_state = H::combine(std::move(inner_state), *begin); + cb(inner_state); + } + } + }; }; // is_uniquely_represented @@ -343,17 +426,43 @@ H AbslHashValue(H hash_state, std::nullptr_t) { return H::combine(std::move(hash_state), static_cast<void*>(nullptr)); } +// AbslHashValue() for hashing pointers-to-member +template <typename H, typename T, typename C> +H AbslHashValue(H hash_state, T C::*ptr) { + auto salient_ptm_size = [](std::size_t n) -> std::size_t { +#if defined(_MSC_VER) + // Pointers-to-member-function on MSVC consist of one pointer plus 0, 1, 2, + // or 3 ints. In 64-bit mode, they are 8-byte aligned and thus can contain + // padding (namely when they have 1 or 3 ints). The value below is a lower + // bound on the number of salient, non-padding bytes that we use for + // hashing. + if (alignof(T C::*) == alignof(int)) { + // No padding when all subobjects have the same size as the total + // alignment. This happens in 32-bit mode. + return n; + } else { + // Padding for 1 int (size 16) or 3 ints (size 24). + // With 2 ints, the size is 16 with no padding, which we pessimize. + return n == 24 ? 20 : n == 16 ? 12 : n; + } +#else + // On other platforms, we assume that pointers-to-members do not have + // padding. +#ifdef __cpp_lib_has_unique_object_representations + static_assert(std::has_unique_object_representations<T C::*>::value); +#endif // __cpp_lib_has_unique_object_representations + return n; +#endif + }; + return H::combine_contiguous(std::move(hash_state), + reinterpret_cast<unsigned char*>(&ptr), + salient_ptm_size(sizeof ptr)); +} + // ----------------------------------------------------------------------------- // AbslHashValue for Composite Types // ----------------------------------------------------------------------------- -// is_hashable() -// -// Trait class which returns true if T is hashable by the absl::Hash framework. -// Used for the AbslHashValue implementations for composite types below. -template <typename T> -struct is_hashable; - // AbslHashValue() for hashing pairs template <typename H, typename T1, typename T2> typename std::enable_if<is_hashable<T1>::value && is_hashable<T2>::value, @@ -377,7 +486,7 @@ template <typename H, typename... Ts> // This SFINAE gets MSVC confused under some conditions. Let's just disable it // for now. H -#else // _MSC_VER +#else // _MSC_VER typename std::enable_if<absl::conjunction<is_hashable<Ts>...>::value, H>::type #endif // _MSC_VER AbslHashValue(H hash_state, const std::tuple<Ts...>& t) { @@ -411,14 +520,15 @@ H AbslHashValue(H hash_state, const std::shared_ptr<T>& ptr) { // the same character sequence. These types are: // // - `absl::Cord` -// - `std::string` (and std::basic_string<char, std::char_traits<char>, A> for -// any allocator A) -// - `absl::string_view` and `std::string_view` -// -// For simplicity, we currently support only `char` strings. This support may -// be broadened, if necessary, but with some caution - this overload would -// misbehave in cases where the traits' `eq()` member isn't equivalent to `==` -// on the underlying character type. +// - `std::string` (and std::basic_string<T, std::char_traits<T>, A> for +// any allocator A and any T in {char, wchar_t, char16_t, char32_t}) +// - `absl::string_view`, `std::string_view`, `std::wstring_view`, +// `std::u16string_view`, and `std::u32_string_view`. +// +// For simplicity, we currently support only strings built on `char`, `wchar_t`, +// `char16_t`, or `char32_t`. This support may be broadened, if necessary, but +// with some caution - this overload would misbehave in cases where the traits' +// `eq()` member isn't equivalent to `==` on the underlying character type. template <typename H> H AbslHashValue(H hash_state, absl::string_view str) { return H::combine( @@ -439,6 +549,21 @@ H AbslHashValue( str.size()); } +#ifdef ABSL_HAVE_STD_STRING_VIEW + +// Support std::wstring_view, std::u16string_view and std::u32string_view. +template <typename Char, typename H, + typename = absl::enable_if_t<std::is_same<Char, wchar_t>::value || + std::is_same<Char, char16_t>::value || + std::is_same<Char, char32_t>::value>> +H AbslHashValue(H hash_state, std::basic_string_view<Char> str) { + return H::combine( + H::combine_contiguous(std::move(hash_state), str.data(), str.size()), + str.size()); +} + +#endif // ABSL_HAVE_STD_STRING_VIEW + // ----------------------------------------------------------------------------- // AbslHashValue for Sequence Containers // ----------------------------------------------------------------------------- @@ -487,8 +612,9 @@ typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue( // AbslHashValue for hashing std::vector // -// Do not use this for vector<bool>. It does not have a .data(), and a fallback -// for std::hash<> is most likely faster. +// Do not use this for vector<bool> on platforms that have a working +// implementation of std::hash. It does not have a .data(), and a fallback for +// std::hash<> is most likely faster. template <typename H, typename T, typename Allocator> typename std::enable_if<is_hashable<T>::value && !std::is_same<T, bool>::value, H>::type @@ -498,6 +624,44 @@ AbslHashValue(H hash_state, const std::vector<T, Allocator>& vector) { vector.size()); } +// AbslHashValue special cases for hashing std::vector<bool> + +#if defined(ABSL_IS_BIG_ENDIAN) && \ + (defined(__GLIBCXX__) || defined(__GLIBCPP__)) + +// std::hash in libstdc++ does not work correctly with vector<bool> on Big +// Endian platforms therefore we need to implement a custom AbslHashValue for +// it. More details on the bug: +// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102531 +template <typename H, typename T, typename Allocator> +typename std::enable_if<is_hashable<T>::value && std::is_same<T, bool>::value, + H>::type +AbslHashValue(H hash_state, const std::vector<T, Allocator>& vector) { + typename H::AbslInternalPiecewiseCombiner combiner; + for (const auto& i : vector) { + unsigned char c = static_cast<unsigned char>(i); + hash_state = combiner.add_buffer(std::move(hash_state), &c, sizeof(c)); + } + return H::combine(combiner.finalize(std::move(hash_state)), vector.size()); +} +#else +// When not working around the libstdc++ bug above, we still have to contend +// with the fact that std::hash<vector<bool>> is often poor quality, hashing +// directly on the internal words and on no other state. On these platforms, +// vector<bool>{1, 1} and vector<bool>{1, 1, 0} hash to the same value. +// +// Mixing in the size (as we do in our other vector<> implementations) on top +// of the library-provided hash implementation avoids this QOI issue. +template <typename H, typename T, typename Allocator> +typename std::enable_if<is_hashable<T>::value && std::is_same<T, bool>::value, + H>::type +AbslHashValue(H hash_state, const std::vector<T, Allocator>& vector) { + return H::combine(std::move(hash_state), + std::hash<std::vector<T, Allocator>>{}(vector), + vector.size()); +} +#endif + // ----------------------------------------------------------------------------- // AbslHashValue for Ordered Associative Containers // ----------------------------------------------------------------------------- @@ -548,6 +712,55 @@ typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue( } // ----------------------------------------------------------------------------- +// AbslHashValue for Unordered Associative Containers +// ----------------------------------------------------------------------------- + +// AbslHashValue for hashing std::unordered_set +template <typename H, typename Key, typename Hash, typename KeyEqual, + typename Alloc> +typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue( + H hash_state, const std::unordered_set<Key, Hash, KeyEqual, Alloc>& s) { + return H::combine( + H::combine_unordered(std::move(hash_state), s.begin(), s.end()), + s.size()); +} + +// AbslHashValue for hashing std::unordered_multiset +template <typename H, typename Key, typename Hash, typename KeyEqual, + typename Alloc> +typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue( + H hash_state, + const std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& s) { + return H::combine( + H::combine_unordered(std::move(hash_state), s.begin(), s.end()), + s.size()); +} + +// AbslHashValue for hashing std::unordered_set +template <typename H, typename Key, typename T, typename Hash, + typename KeyEqual, typename Alloc> +typename std::enable_if<is_hashable<Key>::value && is_hashable<T>::value, + H>::type +AbslHashValue(H hash_state, + const std::unordered_map<Key, T, Hash, KeyEqual, Alloc>& s) { + return H::combine( + H::combine_unordered(std::move(hash_state), s.begin(), s.end()), + s.size()); +} + +// AbslHashValue for hashing std::unordered_multiset +template <typename H, typename Key, typename T, typename Hash, + typename KeyEqual, typename Alloc> +typename std::enable_if<is_hashable<Key>::value && is_hashable<T>::value, + H>::type +AbslHashValue(H hash_state, + const std::unordered_multimap<Key, T, Hash, KeyEqual, Alloc>& s) { + return H::combine( + H::combine_unordered(std::move(hash_state), s.begin(), s.end()), + s.size()); +} + +// ----------------------------------------------------------------------------- // AbslHashValue for Wrapper Types // ----------------------------------------------------------------------------- @@ -590,9 +803,28 @@ AbslHashValue(H hash_state, const absl::variant<T...>& v) { // AbslHashValue for Other Types // ----------------------------------------------------------------------------- -// AbslHashValue for hashing std::bitset is not defined, for the same reason as -// for vector<bool> (see std::vector above): It does not expose the raw bytes, -// and a fallback to std::hash<> is most likely faster. +// AbslHashValue for hashing std::bitset is not defined on Little Endian +// platforms, for the same reason as for vector<bool> (see std::vector above): +// It does not expose the raw bytes, and a fallback to std::hash<> is most +// likely faster. + +#if defined(ABSL_IS_BIG_ENDIAN) && \ + (defined(__GLIBCXX__) || defined(__GLIBCPP__)) +// AbslHashValue for hashing std::bitset +// +// std::hash in libstdc++ does not work correctly with std::bitset on Big Endian +// platforms therefore we need to implement a custom AbslHashValue for it. More +// details on the bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102531 +template <typename H, size_t N> +H AbslHashValue(H hash_state, const std::bitset<N>& set) { + typename H::AbslInternalPiecewiseCombiner combiner; + for (int i = 0; i < N; i++) { + unsigned char c = static_cast<unsigned char>(set[i]); + hash_state = combiner.add_buffer(std::move(hash_state), &c, sizeof(c)); + } + return H::combine(combiner.finalize(std::move(hash_state)), N); +} +#endif // ----------------------------------------------------------------------------- @@ -712,9 +944,8 @@ template <typename T> struct is_hashable : std::integral_constant<bool, HashSelect::template Apply<T>::value> {}; -// CityHashState -class ABSL_DLL CityHashState - : public HashStateBase<CityHashState> { +// MixingHashState +class ABSL_DLL MixingHashState : public HashStateBase<MixingHashState> { // absl::uint128 is not an alias or a thin wrapper around the intrinsic. // We use the intrinsic when available to improve performance. #ifdef ABSL_HAVE_INTRINSIC_INT128 @@ -724,8 +955,8 @@ class ABSL_DLL CityHashState #endif // ABSL_HAVE_INTRINSIC_INT128 static constexpr uint64_t kMul = - sizeof(size_t) == 4 ? uint64_t{0xcc9e2d51} - : uint64_t{0x9ddfea08eb382d69}; + sizeof(size_t) == 4 ? uint64_t{0xcc9e2d51} + : uint64_t{0x9ddfea08eb382d69}; template <typename T> using IntegralFastPath = @@ -733,23 +964,23 @@ class ABSL_DLL CityHashState public: // Move only - CityHashState(CityHashState&&) = default; - CityHashState& operator=(CityHashState&&) = default; + MixingHashState(MixingHashState&&) = default; + MixingHashState& operator=(MixingHashState&&) = default; - // CityHashState::combine_contiguous() + // MixingHashState::combine_contiguous() // // Fundamental base case for hash recursion: mixes the given range of bytes // into the hash state. - static CityHashState combine_contiguous(CityHashState hash_state, - const unsigned char* first, - size_t size) { - return CityHashState( + static MixingHashState combine_contiguous(MixingHashState hash_state, + const unsigned char* first, + size_t size) { + return MixingHashState( CombineContiguousImpl(hash_state.state_, first, size, std::integral_constant<int, sizeof(size_t)>{})); } - using CityHashState::HashStateBase::combine_contiguous; + using MixingHashState::HashStateBase::combine_contiguous; - // CityHashState::hash() + // MixingHashState::hash() // // For performance reasons in non-opt mode, we specialize this for // integral types. @@ -758,27 +989,53 @@ class ABSL_DLL CityHashState // The result should be the same as running the whole algorithm, but faster. template <typename T, absl::enable_if_t<IntegralFastPath<T>::value, int> = 0> static size_t hash(T value) { - return static_cast<size_t>(Mix(Seed(), static_cast<uint64_t>(value))); + return static_cast<size_t>( + Mix(Seed(), static_cast<std::make_unsigned_t<T>>(value))); } - // Overload of CityHashState::hash() + // Overload of MixingHashState::hash() template <typename T, absl::enable_if_t<!IntegralFastPath<T>::value, int> = 0> static size_t hash(const T& value) { - return static_cast<size_t>(combine(CityHashState{}, value).state_); + return static_cast<size_t>(combine(MixingHashState{}, value).state_); } private: // Invoked only once for a given argument; that plus the fact that this is // move-only ensures that there is only one non-moved-from object. - CityHashState() : state_(Seed()) {} + MixingHashState() : state_(Seed()) {} + + friend class MixingHashState::HashStateBase; + + template <typename CombinerT> + static MixingHashState RunCombineUnordered(MixingHashState state, + CombinerT combiner) { + uint64_t unordered_state = 0; + combiner(MixingHashState{}, [&](MixingHashState& inner_state) { + // Add the hash state of the element to the running total, but mix the + // carry bit back into the low bit. This in intended to avoid losing + // entropy to overflow, especially when unordered_multisets contain + // multiple copies of the same value. + auto element_state = inner_state.state_; + unordered_state += element_state; + if (unordered_state < element_state) { + ++unordered_state; + } + inner_state = MixingHashState{}; + }); + return MixingHashState::combine(std::move(state), unordered_state); + } + + // Allow the HashState type-erasure implementation to invoke + // RunCombinedUnordered() directly. + friend class absl::HashState; // Workaround for MSVC bug. // We make the type copyable to fix the calling convention, even though we // never actually copy it. Keep it private to not affect the public API of the // type. - CityHashState(const CityHashState&) = default; + MixingHashState(const MixingHashState&) = default; - explicit CityHashState(uint64_t state) : state_(state) {} + explicit MixingHashState(uint64_t state) : state_(state) {} // Implementation of the base case for combine_contiguous where we actually // mix the bytes into the state. @@ -791,7 +1048,7 @@ class ABSL_DLL CityHashState static uint64_t CombineContiguousImpl(uint64_t state, const unsigned char* first, size_t len, std::integral_constant<int, 8> - /* sizeof_size_t*/); + /* sizeof_size_t */); // Slow dispatch path for calls to CombineContiguousImpl with a size argument // larger than PiecewiseChunkSize(). Has the same effect as calling @@ -804,29 +1061,60 @@ class ABSL_DLL CityHashState size_t len); // Reads 9 to 16 bytes from p. - // The first 8 bytes are in .first, the rest (zero padded) bytes are in - // .second. + // The least significant 8 bytes are in .first, the rest (zero padded) bytes + // are in .second. static std::pair<uint64_t, uint64_t> Read9To16(const unsigned char* p, size_t len) { - uint64_t high = little_endian::Load64(p + len - 8); - return {little_endian::Load64(p), high >> (128 - len * 8)}; + uint64_t low_mem = absl::base_internal::UnalignedLoad64(p); + uint64_t high_mem = absl::base_internal::UnalignedLoad64(p + len - 8); +#ifdef ABSL_IS_LITTLE_ENDIAN + uint64_t most_significant = high_mem; + uint64_t least_significant = low_mem; +#else + uint64_t most_significant = low_mem; + uint64_t least_significant = high_mem; +#endif + return {least_significant, most_significant}; } // Reads 4 to 8 bytes from p. Zero pads to fill uint64_t. static uint64_t Read4To8(const unsigned char* p, size_t len) { - return (static_cast<uint64_t>(little_endian::Load32(p + len - 4)) - << (len - 4) * 8) | - little_endian::Load32(p); + uint32_t low_mem = absl::base_internal::UnalignedLoad32(p); + uint32_t high_mem = absl::base_internal::UnalignedLoad32(p + len - 4); +#ifdef ABSL_IS_LITTLE_ENDIAN + uint32_t most_significant = high_mem; + uint32_t least_significant = low_mem; +#else + uint32_t most_significant = low_mem; + uint32_t least_significant = high_mem; +#endif + return (static_cast<uint64_t>(most_significant) << (len - 4) * 8) | + least_significant; } // Reads 1 to 3 bytes from p. Zero pads to fill uint32_t. static uint32_t Read1To3(const unsigned char* p, size_t len) { - return static_cast<uint32_t>((p[0]) | // - (p[len / 2] << (len / 2 * 8)) | // - (p[len - 1] << ((len - 1) * 8))); + // The trick used by this implementation is to avoid branches if possible. + unsigned char mem0 = p[0]; + unsigned char mem1 = p[len / 2]; + unsigned char mem2 = p[len - 1]; +#ifdef ABSL_IS_LITTLE_ENDIAN + unsigned char significant2 = mem2; + unsigned char significant1 = mem1; + unsigned char significant0 = mem0; +#else + unsigned char significant2 = mem0; + unsigned char significant1 = len == 2 ? mem0 : mem1; + unsigned char significant0 = mem2; +#endif + return static_cast<uint32_t>(significant0 | // + (significant1 << (len / 2 * 8)) | // + (significant2 << ((len - 1) * 8))); } ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Mix(uint64_t state, uint64_t v) { + // Though the 128-bit product on AArch64 needs two instructions, it is + // still a good balance between speed and hash quality. using MultType = absl::conditional_t<sizeof(size_t) == 4, uint64_t, uint128>; // We do the addition in 64-bit space to make sure the 128-bit @@ -838,6 +1126,19 @@ class ABSL_DLL CityHashState return static_cast<uint64_t>(m ^ (m >> (sizeof(m) * 8 / 2))); } + // An extern to avoid bloat on a direct call to LowLevelHash() with fixed + // values for both the seed and salt parameters. + static uint64_t LowLevelHashImpl(const unsigned char* data, size_t len); + + ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Hash64(const unsigned char* data, + size_t len) { +#ifdef ABSL_HAVE_INTRINSIC_INT128 + return LowLevelHashImpl(data, len); +#else + return hash_internal::CityHash64(reinterpret_cast<const char*>(data), len); +#endif + } + // Seed() // // A non-deterministic seed. @@ -855,15 +1156,23 @@ class ABSL_DLL CityHashState // On other platforms this is still going to be non-deterministic but most // probably per-build and not per-process. ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Seed() { +#if (!defined(__clang__) || __clang_major__ > 11) && \ + (!defined(__apple_build_version__) || \ + __apple_build_version__ >= 19558921) // Xcode 12 + return static_cast<uint64_t>(reinterpret_cast<uintptr_t>(&kSeed)); +#else + // Workaround the absence of + // https://github.com/llvm/llvm-project/commit/bc15bf66dcca76cc06fe71fca35b74dc4d521021. return static_cast<uint64_t>(reinterpret_cast<uintptr_t>(kSeed)); +#endif } static const void* const kSeed; uint64_t state_; }; -// CityHashState::CombineContiguousImpl() -inline uint64_t CityHashState::CombineContiguousImpl( +// MixingHashState::CombineContiguousImpl() +inline uint64_t MixingHashState::CombineContiguousImpl( uint64_t state, const unsigned char* first, size_t len, std::integral_constant<int, 4> /* sizeof_size_t */) { // For large values we use CityHash, for small ones we just use a @@ -873,7 +1182,7 @@ inline uint64_t CityHashState::CombineContiguousImpl( if (ABSL_PREDICT_FALSE(len > PiecewiseChunkSize())) { return CombineLargeContiguousImpl32(state, first, len); } - v = absl::hash_internal::CityHash32(reinterpret_cast<const char*>(first), len); + v = hash_internal::CityHash32(reinterpret_cast<const char*>(first), len); } else if (len >= 4) { v = Read4To8(first, len); } else if (len > 0) { @@ -885,22 +1194,35 @@ inline uint64_t CityHashState::CombineContiguousImpl( return Mix(state, v); } -// Overload of CityHashState::CombineContiguousImpl() -inline uint64_t CityHashState::CombineContiguousImpl( +// Overload of MixingHashState::CombineContiguousImpl() +inline uint64_t MixingHashState::CombineContiguousImpl( uint64_t state, const unsigned char* first, size_t len, std::integral_constant<int, 8> /* sizeof_size_t */) { - // For large values we use CityHash, for small ones we just use a - // multiplicative hash. + // For large values we use LowLevelHash or CityHash depending on the platform, + // for small ones we just use a multiplicative hash. uint64_t v; if (len > 16) { if (ABSL_PREDICT_FALSE(len > PiecewiseChunkSize())) { return CombineLargeContiguousImpl64(state, first, len); } - v = absl::hash_internal::CityHash64(reinterpret_cast<const char*>(first), len); + v = Hash64(first, len); } else if (len > 8) { + // This hash function was constructed by the ML-driven algorithm discovery + // using reinforcement learning. We fed the agent lots of inputs from + // microbenchmarks, SMHasher, low hamming distance from generated inputs and + // picked up the one that was good on micro and macrobenchmarks. auto p = Read9To16(first, len); - state = Mix(state, p.first); - v = p.second; + uint64_t lo = p.first; + uint64_t hi = p.second; + // Rotation by 53 was found to be most often useful when discovering these + // hashing algorithms with ML techniques. + lo = absl::rotr(lo, 53); + state += kMul; + lo += state; + state ^= hi; + uint128 m = state; + m *= lo; + return static_cast<uint64_t>(m ^ (m >> 64)); } else if (len >= 4) { v = Read4To8(first, len); } else if (len > 0) { @@ -927,7 +1249,9 @@ struct PoisonedHash : private AggregateBarrier { template <typename T> struct HashImpl { - size_t operator()(const T& value) const { return CityHashState::hash(value); } + size_t operator()(const T& value) const { + return MixingHashState::hash(value); + } }; template <typename T> @@ -949,6 +1273,14 @@ H HashStateBase<H>::combine_contiguous(H state, const T* data, size_t size) { return hash_internal::hash_range_or_bytes(std::move(state), data, size); } +// HashStateBase::combine_unordered() +template <typename H> +template <typename I> +H HashStateBase<H>::combine_unordered(H state, I begin, I end) { + return H::RunCombineUnordered(std::move(state), + CombineUnorderedCallback<I>{begin, end}); +} + // HashStateBase::PiecewiseCombiner::add_buffer() template <typename H> H PiecewiseCombiner::add_buffer(H state, const unsigned char* data, |