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authorGravatar Abseil Team <absl-team@google.com>2018-12-04 11:01:12 -0800
committerGravatar Ashley Hedberg <ahedberg@google.com>2018-12-04 16:54:40 -0500
commitfcb104594b0bb4b8ac306cb2f55ecdad40974683 (patch)
treed2d79d246c6a894ca6716f47c15ebb7b8796b36a /absl/hash/internal/hash.h
parent6c7de165d1c82684359ccb630bb5f83263fa5ebc (diff)
Creation of LTS branch "lts_2018_12_18"20181200
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diff --git a/absl/hash/internal/hash.h b/absl/hash/internal/hash.h
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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
+//
+// 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
+// -----------------------------------------------------------------------------
+//
+#ifndef ABSL_HASH_INTERNAL_HASH_H_
+#define ABSL_HASH_INTERNAL_HASH_H_
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <cstring>
+#include <deque>
+#include <forward_list>
+#include <functional>
+#include <iterator>
+#include <limits>
+#include <list>
+#include <map>
+#include <memory>
+#include <set>
+#include <string>
+#include <tuple>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include "absl/base/internal/endian.h"
+#include "absl/base/port.h"
+#include "absl/container/fixed_array.h"
+#include "absl/meta/type_traits.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"
+
+namespace absl {
+inline namespace lts_2018_12_18 {
+namespace hash_internal {
+
+// 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:
+//
+// * HashStateBase::combine()
+// * HashStateBase::combine_contiguous()
+//
+// A derived hash state class of type `H` must provide a static member function
+// with a signature similar to the following:
+//
+// `static H combine_contiguous(H state, const unsigned char*, size_t)`.
+//
+// `HashStateBase` will provide a complete implementations for a hash state
+// object in terms of this method.
+//
+// Example:
+//
+// // Use CRTP to define your derived class.
+// struct MyHashState : HashStateBase<MyHashState> {
+// static H combine_contiguous(H state, const unsigned char*, size_t);
+// using MyHashState::HashStateBase::combine;
+// using MyHashState::HashStateBase::combine_contiguous;
+// };
+template <typename H>
+class HashStateBase {
+ public:
+ // HashStateBase::combine()
+ //
+ // Combines an arbitrary number of values into a hash state, returning the
+ // updated state.
+ //
+ // Each of the value types `T` must be separately hashable by the Abseil
+ // hashing framework.
+ //
+ // NOTE:
+ //
+ // state = H::combine(std::move(state), value1, value2, value3);
+ //
+ // is 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);
+ template <typename T, typename... Ts>
+ static H combine(H state, const T& value, const Ts&... values);
+ static H combine(H state) { return state; }
+
+ // HashStateBase::combine_contiguous()
+ //
+ // Combines a contiguous array of `size` elements into a hash state, returning
+ // the updated state.
+ //
+ // NOTE:
+ //
+ // state = H::combine_contiguous(std::move(state), data, size);
+ //
+ // is NOT guaranteed to produce the same hash expansion as a for-loop (it may
+ // perform internal optimizations). If you need this guarantee, use the
+ // for-loop instead.
+ template <typename T>
+ static H combine_contiguous(H state, const T* data, size_t size);
+};
+
+// is_uniquely_represented
+//
+// `is_uniquely_represented<T>` is a trait class that indicates whether `T`
+// is uniquely represented.
+//
+// A type is "uniquely represented" if two equal values of that type are
+// guaranteed to have the same bytes in their underlying storage. In other
+// words, if `a == b`, then `memcmp(&a, &b, sizeof(T))` is guaranteed to be
+// zero. This property cannot be detected automatically, so this trait is false
+// by default, but can be specialized by types that wish to assert that they are
+// uniquely represented. This makes them eligible for certain optimizations.
+//
+// If you have any doubt whatsoever, do not specialize this template.
+// The default is completely safe, and merely disables some optimizations
+// that will not matter for most types. Specializing this template,
+// on the other hand, can be very hazardous.
+//
+// To be uniquely represented, a type must not have multiple ways of
+// representing the same value; for example, float and double are not
+// uniquely represented, because they have distinct representations for
+// +0 and -0. Furthermore, the type's byte representation must consist
+// solely of user-controlled data, with no padding bits and no compiler-
+// controlled data such as vptrs or sanitizer metadata. This is usually
+// very difficult to guarantee, because in most cases the compiler can
+// insert data and padding bits at its own discretion.
+//
+// If you specialize this template for a type `T`, you must do so in the file
+// that defines that type (or in this file). If you define that specialization
+// anywhere else, `is_uniquely_represented<T>` could have different meanings
+// in different places.
+//
+// The Enable parameter is meaningless; it is provided as a convenience,
+// to support certain SFINAE techniques when defining specializations.
+template <typename T, typename Enable = void>
+struct is_uniquely_represented : std::false_type {};
+
+// is_uniquely_represented<unsigned char>
+//
+// unsigned char is a synonym for "byte", so it is guaranteed to be
+// uniquely represented.
+template <>
+struct is_uniquely_represented<unsigned char> : std::true_type {};
+
+// is_uniquely_represented for non-standard integral types
+//
+// Integral types other than bool should be uniquely represented on any
+// platform that this will plausibly be ported to.
+template <typename Integral>
+struct is_uniquely_represented<
+ Integral, typename std::enable_if<std::is_integral<Integral>::value>::type>
+ : std::true_type {};
+
+// is_uniquely_represented<bool>
+//
+//
+template <>
+struct is_uniquely_represented<bool> : std::false_type {};
+
+// hash_bytes()
+//
+// Convenience function that combines `hash_state` with the byte representation
+// of `value`.
+template <typename H, typename T>
+H hash_bytes(H hash_state, const T& value) {
+ const unsigned char* start = reinterpret_cast<const unsigned char*>(&value);
+ return H::combine_contiguous(std::move(hash_state), start, sizeof(value));
+}
+
+// -----------------------------------------------------------------------------
+// AbslHashValue for Basic Types
+// -----------------------------------------------------------------------------
+
+// Note: Default `AbslHashValue` implementations live in `hash_internal`. This
+// allows us to block lexical scope lookup when doing an unqualified call to
+// `AbslHashValue` below. User-defined implementations of `AbslHashValue` can
+// only be found via ADL.
+
+// AbslHashValue() for hashing bool values
+//
+// We use SFINAE to ensure that this overload only accepts bool, not types that
+// are convertible to bool.
+template <typename H, typename B>
+typename std::enable_if<std::is_same<B, bool>::value, H>::type AbslHashValue(
+ H hash_state, B value) {
+ return H::combine(std::move(hash_state),
+ static_cast<unsigned char>(value ? 1 : 0));
+}
+
+// AbslHashValue() for hashing enum values
+template <typename H, typename Enum>
+typename std::enable_if<std::is_enum<Enum>::value, H>::type AbslHashValue(
+ H hash_state, Enum e) {
+ // In practice, we could almost certainly just invoke hash_bytes directly,
+ // but it's possible that a sanitizer might one day want to
+ // store data in the unused bits of an enum. To avoid that risk, we
+ // convert to the underlying type before hashing. Hopefully this will get
+ // optimized away; if not, we can reopen discussion with c-toolchain-team.
+ return H::combine(std::move(hash_state),
+ static_cast<typename std::underlying_type<Enum>::type>(e));
+}
+// AbslHashValue() for hashing floating-point values
+template <typename H, typename Float>
+typename std::enable_if<std::is_floating_point<Float>::value, H>::type
+AbslHashValue(H hash_state, Float value) {
+ return hash_internal::hash_bytes(std::move(hash_state),
+ value == 0 ? 0 : value);
+}
+
+// Long double has the property that it might have extra unused bytes in it.
+// For example, in x86 sizeof(long double)==16 but it only really uses 80-bits
+// of it. This means we can't use hash_bytes on a long double and have to
+// convert it to something else first.
+template <typename H>
+H AbslHashValue(H hash_state, long double value) {
+ const int category = std::fpclassify(value);
+ switch (category) {
+ case FP_INFINITE:
+ // Add the sign bit to differentiate between +Inf and -Inf
+ hash_state = H::combine(std::move(hash_state), std::signbit(value));
+ break;
+
+ case FP_NAN:
+ case FP_ZERO:
+ default:
+ // Category is enough for these.
+ break;
+
+ case FP_NORMAL:
+ case FP_SUBNORMAL:
+ // We can't convert `value` directly to double because this would have
+ // undefined behavior if the value is out of range.
+ // std::frexp gives us a value in the range (-1, -.5] or [.5, 1) that is
+ // guaranteed to be in range for `double`. The truncation is
+ // implementation defined, but that works as long as it is deterministic.
+ int exp;
+ auto mantissa = static_cast<double>(std::frexp(value, &exp));
+ hash_state = H::combine(std::move(hash_state), mantissa, exp);
+ }
+
+ return H::combine(std::move(hash_state), category);
+}
+
+// AbslHashValue() for hashing pointers
+template <typename H, typename T>
+H AbslHashValue(H hash_state, T* ptr) {
+ return hash_internal::hash_bytes(std::move(hash_state), ptr);
+}
+
+// AbslHashValue() for hashing nullptr_t
+template <typename H>
+H AbslHashValue(H hash_state, std::nullptr_t) {
+ return H::combine(std::move(hash_state), static_cast<void*>(nullptr));
+}
+
+// -----------------------------------------------------------------------------
+// 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,
+ H>::type
+AbslHashValue(H hash_state, const std::pair<T1, T2>& p) {
+ return H::combine(std::move(hash_state), p.first, p.second);
+}
+
+// hash_tuple()
+//
+// Helper function for hashing a tuple. The third argument should
+// be an index_sequence running from 0 to tuple_size<Tuple> - 1.
+template <typename H, typename Tuple, size_t... Is>
+H hash_tuple(H hash_state, const Tuple& t, absl::index_sequence<Is...>) {
+ return H::combine(std::move(hash_state), std::get<Is>(t)...);
+}
+
+// AbslHashValue for hashing tuples
+template <typename H, typename... Ts>
+#if defined(_MSC_VER)
+// This SFINAE gets MSVC confused under some conditions. Let's just disable it
+// for now.
+H
+#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) {
+ return hash_internal::hash_tuple(std::move(hash_state), t,
+ absl::make_index_sequence<sizeof...(Ts)>());
+}
+
+// -----------------------------------------------------------------------------
+// AbslHashValue for Pointers
+// -----------------------------------------------------------------------------
+
+// AbslHashValue for hashing unique_ptr
+template <typename H, typename T, typename D>
+H AbslHashValue(H hash_state, const std::unique_ptr<T, D>& ptr) {
+ return H::combine(std::move(hash_state), ptr.get());
+}
+
+// AbslHashValue for hashing shared_ptr
+template <typename H, typename T>
+H AbslHashValue(H hash_state, const std::shared_ptr<T>& ptr) {
+ return H::combine(std::move(hash_state), ptr.get());
+}
+
+// -----------------------------------------------------------------------------
+// AbslHashValue for String-Like Types
+// -----------------------------------------------------------------------------
+
+// AbslHashValue for hashing strings
+//
+// All the string-like types supported here provide the same hash expansion for
+// the same character sequence. These types are:
+//
+// - `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.
+template <typename H>
+H AbslHashValue(H hash_state, absl::string_view str) {
+ return H::combine(
+ H::combine_contiguous(std::move(hash_state), str.data(), str.size()),
+ str.size());
+}
+
+// -----------------------------------------------------------------------------
+// AbslHashValue for Sequence Containers
+// -----------------------------------------------------------------------------
+
+// AbslHashValue for hashing std::array
+template <typename H, typename T, size_t N>
+typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
+ H hash_state, const std::array<T, N>& array) {
+ return H::combine_contiguous(std::move(hash_state), array.data(),
+ array.size());
+}
+
+// AbslHashValue for hashing std::deque
+template <typename H, typename T, typename Allocator>
+typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
+ H hash_state, const std::deque<T, Allocator>& deque) {
+ // TODO(gromer): investigate a more efficient implementation taking
+ // advantage of the chunk structure.
+ for (const auto& t : deque) {
+ hash_state = H::combine(std::move(hash_state), t);
+ }
+ return H::combine(std::move(hash_state), deque.size());
+}
+
+// AbslHashValue for hashing std::forward_list
+template <typename H, typename T, typename Allocator>
+typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
+ H hash_state, const std::forward_list<T, Allocator>& list) {
+ size_t size = 0;
+ for (const T& t : list) {
+ hash_state = H::combine(std::move(hash_state), t);
+ ++size;
+ }
+ return H::combine(std::move(hash_state), size);
+}
+
+// AbslHashValue for hashing std::list
+template <typename H, typename T, typename Allocator>
+typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
+ H hash_state, const std::list<T, Allocator>& list) {
+ for (const auto& t : list) {
+ hash_state = H::combine(std::move(hash_state), t);
+ }
+ return H::combine(std::move(hash_state), list.size());
+}
+
+// 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.
+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(H::combine_contiguous(std::move(hash_state), vector.data(),
+ vector.size()),
+ vector.size());
+}
+
+// -----------------------------------------------------------------------------
+// AbslHashValue for Ordered Associative Containers
+// -----------------------------------------------------------------------------
+
+// AbslHashValue for hashing std::map
+template <typename H, typename Key, typename T, typename Compare,
+ typename Allocator>
+typename std::enable_if<is_hashable<Key>::value && is_hashable<T>::value,
+ H>::type
+AbslHashValue(H hash_state, const std::map<Key, T, Compare, Allocator>& map) {
+ for (const auto& t : map) {
+ hash_state = H::combine(std::move(hash_state), t);
+ }
+ return H::combine(std::move(hash_state), map.size());
+}
+
+// AbslHashValue for hashing std::multimap
+template <typename H, typename Key, typename T, typename Compare,
+ typename Allocator>
+typename std::enable_if<is_hashable<Key>::value && is_hashable<T>::value,
+ H>::type
+AbslHashValue(H hash_state,
+ const std::multimap<Key, T, Compare, Allocator>& map) {
+ for (const auto& t : map) {
+ hash_state = H::combine(std::move(hash_state), t);
+ }
+ return H::combine(std::move(hash_state), map.size());
+}
+
+// AbslHashValue for hashing std::set
+template <typename H, typename Key, typename Compare, typename Allocator>
+typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue(
+ H hash_state, const std::set<Key, Compare, Allocator>& set) {
+ for (const auto& t : set) {
+ hash_state = H::combine(std::move(hash_state), t);
+ }
+ return H::combine(std::move(hash_state), set.size());
+}
+
+// AbslHashValue for hashing std::multiset
+template <typename H, typename Key, typename Compare, typename Allocator>
+typename std::enable_if<is_hashable<Key>::value, H>::type AbslHashValue(
+ H hash_state, const std::multiset<Key, Compare, Allocator>& set) {
+ for (const auto& t : set) {
+ hash_state = H::combine(std::move(hash_state), t);
+ }
+ return H::combine(std::move(hash_state), set.size());
+}
+
+// -----------------------------------------------------------------------------
+// AbslHashValue for Wrapper Types
+// -----------------------------------------------------------------------------
+
+// AbslHashValue for hashing absl::optional
+template <typename H, typename T>
+typename std::enable_if<is_hashable<T>::value, H>::type AbslHashValue(
+ H hash_state, const absl::optional<T>& opt) {
+ if (opt) hash_state = H::combine(std::move(hash_state), *opt);
+ return H::combine(std::move(hash_state), opt.has_value());
+}
+
+// VariantVisitor
+template <typename H>
+struct VariantVisitor {
+ H&& hash_state;
+ template <typename T>
+ H operator()(const T& t) const {
+ return H::combine(std::move(hash_state), t);
+ }
+};
+
+// AbslHashValue for hashing absl::variant
+template <typename H, typename... T>
+typename std::enable_if<conjunction<is_hashable<T>...>::value, H>::type
+AbslHashValue(H hash_state, const absl::variant<T...>& v) {
+ if (!v.valueless_by_exception()) {
+ hash_state = absl::visit(VariantVisitor<H>{std::move(hash_state)}, v);
+ }
+ return H::combine(std::move(hash_state), v.index());
+}
+
+// -----------------------------------------------------------------------------
+// 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.
+
+// -----------------------------------------------------------------------------
+
+// hash_range_or_bytes()
+//
+// Mixes all values in the range [data, data+size) into the hash state.
+// This overload accepts only uniquely-represented types, and hashes them by
+// hashing the entire range of bytes.
+template <typename H, typename T>
+typename std::enable_if<is_uniquely_represented<T>::value, H>::type
+hash_range_or_bytes(H hash_state, const T* data, size_t size) {
+ const auto* bytes = reinterpret_cast<const unsigned char*>(data);
+ return H::combine_contiguous(std::move(hash_state), bytes, sizeof(T) * size);
+}
+
+// hash_range_or_bytes()
+template <typename H, typename T>
+typename std::enable_if<!is_uniquely_represented<T>::value, H>::type
+hash_range_or_bytes(H hash_state, const T* data, size_t size) {
+ for (const auto end = data + size; data < end; ++data) {
+ hash_state = H::combine(std::move(hash_state), *data);
+ }
+ return hash_state;
+}
+
+// InvokeHashTag
+//
+// InvokeHash(H, const T&) invokes the appropriate hash implementation for a
+// hasher of type `H` and a value of type `T`. If `T` is not hashable, there
+// will be no matching overload of InvokeHash().
+// Note: Some platforms (eg MSVC) do not support the detect idiom on
+// std::hash. In those platforms the last fallback will be std::hash and
+// InvokeHash() will always have a valid overload even if std::hash<T> is not
+// valid.
+//
+// We try the following options in order:
+// * If is_uniquely_represented, hash bytes directly.
+// * ADL AbslHashValue(H, const T&) call.
+// * std::hash<T>
+
+// In MSVC we can't probe std::hash or stdext::hash because it triggers a
+// static_assert instead of failing substitution.
+#if defined(_MSC_VER)
+#define ABSL_HASH_INTERNAL_CAN_POISON_ 0
+#else // _MSC_VER
+#define ABSL_HASH_INTERNAL_CAN_POISON_ 1
+#endif // _MSC_VER
+
+#if defined(ABSL_INTERNAL_LEGACY_HASH_NAMESPACE) && \
+ ABSL_HASH_INTERNAL_CAN_POISON_
+#define ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ 1
+#else
+#define ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_ 0
+#endif
+
+enum class InvokeHashTag {
+ kUniquelyRepresented,
+ kHashValue,
+#if ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
+ kLegacyHash,
+#endif // ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
+ kStdHash,
+ kNone
+};
+
+// HashSelect
+//
+// Type trait to select the appropriate hash implementation to use.
+// HashSelect<T>::value is an instance of InvokeHashTag that indicates the best
+// available hashing mechanism.
+// See `Note` above about MSVC.
+template <typename T>
+struct HashSelect {
+ private:
+ struct State : HashStateBase<State> {
+ static State combine_contiguous(State hash_state, const unsigned char*,
+ size_t);
+ using State::HashStateBase::combine_contiguous;
+ };
+
+ // `Probe<V, Tag>::value` evaluates to `V<T>::value` if it is a valid
+ // expression, and `false` otherwise.
+ // `Probe<V, Tag>::tag` always evaluates to `Tag`.
+ template <template <typename> class V, InvokeHashTag Tag>
+ struct Probe {
+ private:
+ template <typename U, typename std::enable_if<V<U>::value, int>::type = 0>
+ static std::true_type Test(int);
+ template <typename U>
+ static std::false_type Test(char);
+
+ public:
+ static constexpr InvokeHashTag kTag = Tag;
+ static constexpr bool value = decltype(
+ Test<absl::remove_const_t<absl::remove_reference_t<T>>>(0))::value;
+ };
+
+ template <typename U>
+ using ProbeUniquelyRepresented = is_uniquely_represented<U>;
+
+ template <typename U>
+ using ProbeHashValue =
+ std::is_same<State, decltype(AbslHashValue(std::declval<State>(),
+ std::declval<const U&>()))>;
+
+#if ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
+ template <typename U>
+ using ProbeLegacyHash =
+ std::is_convertible<decltype(ABSL_INTERNAL_LEGACY_HASH_NAMESPACE::hash<
+ U>()(std::declval<const U&>())),
+ size_t>;
+#endif // ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
+
+ template <typename U>
+ using ProbeStdHash =
+#if ABSL_HASH_INTERNAL_CAN_POISON_
+ std::is_convertible<decltype(std::hash<U>()(std::declval<const U&>())),
+ size_t>;
+#else // ABSL_HASH_INTERNAL_CAN_POISON_
+ std::true_type;
+#endif // ABSL_HASH_INTERNAL_CAN_POISON_
+
+ template <typename U>
+ using ProbeNone = std::true_type;
+
+ public:
+ // Probe each implementation in order.
+ // disjunction provides short circuting wrt instantiation.
+ static constexpr InvokeHashTag value = absl::disjunction<
+ Probe<ProbeUniquelyRepresented, InvokeHashTag::kUniquelyRepresented>,
+ Probe<ProbeHashValue, InvokeHashTag::kHashValue>,
+#if ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
+ Probe<ProbeLegacyHash, InvokeHashTag::kLegacyHash>,
+#endif // ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
+ Probe<ProbeStdHash, InvokeHashTag::kStdHash>,
+ Probe<ProbeNone, InvokeHashTag::kNone>>::kTag;
+};
+
+template <typename T>
+struct is_hashable : std::integral_constant<bool, HashSelect<T>::value !=
+ InvokeHashTag::kNone> {};
+
+template <typename H, typename T>
+absl::enable_if_t<HashSelect<T>::value == InvokeHashTag::kUniquelyRepresented,
+ H>
+InvokeHash(H state, const T& value) {
+ return hash_internal::hash_bytes(std::move(state), value);
+}
+
+template <typename H, typename T>
+absl::enable_if_t<HashSelect<T>::value == InvokeHashTag::kHashValue, H>
+InvokeHash(H state, const T& value) {
+ return AbslHashValue(std::move(state), value);
+}
+
+#if ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
+template <typename H, typename T>
+absl::enable_if_t<HashSelect<T>::value == InvokeHashTag::kLegacyHash, H>
+InvokeHash(H state, const T& value) {
+ return hash_internal::hash_bytes(
+ std::move(state), ABSL_INTERNAL_LEGACY_HASH_NAMESPACE::hash<T>{}(value));
+}
+#endif // ABSL_HASH_INTERNAL_SUPPORT_LEGACY_HASH_
+
+template <typename H, typename T>
+absl::enable_if_t<HashSelect<T>::value == InvokeHashTag::kStdHash, H>
+InvokeHash(H state, const T& value) {
+ return hash_internal::hash_bytes(std::move(state), std::hash<T>{}(value));
+}
+
+// CityHashState
+class CityHashState : public HashStateBase<CityHashState> {
+ // 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
+ using uint128 = __uint128_t;
+#else // ABSL_HAVE_INTRINSIC_INT128
+ using uint128 = absl::uint128;
+#endif // ABSL_HAVE_INTRINSIC_INT128
+
+ static constexpr uint64_t kMul =
+ sizeof(size_t) == 4 ? uint64_t{0xcc9e2d51} : uint64_t{0x9ddfea08eb382d69};
+
+ template <typename T>
+ using IntegralFastPath =
+ conjunction<std::is_integral<T>, is_uniquely_represented<T>>;
+
+ public:
+ // Move only
+ CityHashState(CityHashState&&) = default;
+ CityHashState& operator=(CityHashState&&) = default;
+
+ // CityHashState::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(
+ CombineContiguousImpl(hash_state.state_, first, size,
+ std::integral_constant<int, sizeof(size_t)>{}));
+ }
+ using CityHashState::HashStateBase::combine_contiguous;
+
+ // CityHashState::hash()
+ //
+ // For performance reasons in non-opt mode, we specialize this for
+ // integral types.
+ // Otherwise we would be instantiating and calling dozens of functions for
+ // something that is just one multiplication and a couple xor's.
+ // 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)));
+ }
+
+ // Overload of CityHashState::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_);
+ }
+
+ 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()) {}
+
+ // 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;
+
+ explicit CityHashState(uint64_t state) : state_(state) {}
+
+ // Implementation of the base case for combine_contiguous where we actually
+ // mix the bytes into the state.
+ // Dispatch to different implementations of the combine_contiguous depending
+ // on the value of `sizeof(size_t)`.
+ static uint64_t CombineContiguousImpl(uint64_t state,
+ const unsigned char* first, size_t len,
+ std::integral_constant<int, 4>
+ /* sizeof_size_t */);
+ static uint64_t CombineContiguousImpl(uint64_t state,
+ const unsigned char* first, size_t len,
+ std::integral_constant<int, 8>
+ /* sizeof_size_t*/);
+
+ // Reads 9 to 16 bytes from p.
+ // The first 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)};
+ }
+
+ // 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);
+ }
+
+ // 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)));
+ }
+
+ ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Mix(uint64_t state, uint64_t v) {
+ 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
+ // multiplication is fast. If we were to do it as MultType the compiler has
+ // to assume that the high word is non-zero and needs to perform 2
+ // multiplications instead of one.
+ MultType m = state + v;
+ m *= kMul;
+ return static_cast<uint64_t>(m ^ (m >> (sizeof(m) * 8 / 2)));
+ }
+
+ // Seed()
+ //
+ // A non-deterministic seed.
+ //
+ // The current purpose of this seed is to generate non-deterministic results
+ // and prevent having users depend on the particular hash values.
+ // It is not meant as a security feature right now, but it leaves the door
+ // open to upgrade it to a true per-process random seed. A true random seed
+ // costs more and we don't need to pay for that right now.
+ //
+ // On platforms with ASLR, we take advantage of it to make a per-process
+ // random value.
+ // See https://en.wikipedia.org/wiki/Address_space_layout_randomization
+ //
+ // 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() {
+ return static_cast<uint64_t>(reinterpret_cast<uintptr_t>(kSeed));
+ }
+ static const void* const kSeed;
+
+ uint64_t state_;
+};
+
+// CityHashState::CombineContiguousImpl()
+inline uint64_t CityHashState::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
+ // multiplicative hash.
+ uint64_t v;
+ if (len > 8) {
+ v = absl::hash_internal::CityHash32(reinterpret_cast<const char*>(first), len);
+ } else if (len >= 4) {
+ v = Read4To8(first, len);
+ } else if (len > 0) {
+ v = Read1To3(first, len);
+ } else {
+ // Empty ranges have no effect.
+ return state;
+ }
+ return Mix(state, v);
+}
+
+// Overload of CityHashState::CombineContiguousImpl()
+inline uint64_t CityHashState::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.
+ uint64_t v;
+ if (len > 16) {
+ v = absl::hash_internal::CityHash64(reinterpret_cast<const char*>(first), len);
+ } else if (len > 8) {
+ auto p = Read9To16(first, len);
+ state = Mix(state, p.first);
+ v = p.second;
+ } else if (len >= 4) {
+ v = Read4To8(first, len);
+ } else if (len > 0) {
+ v = Read1To3(first, len);
+ } else {
+ // Empty ranges have no effect.
+ return state;
+ }
+ return Mix(state, v);
+}
+
+
+struct AggregateBarrier {};
+
+// HashImpl
+
+// Add a private base class to make sure this type is not an aggregate.
+// Aggregates can be aggregate initialized even if the default constructor is
+// deleted.
+struct PoisonedHash : private AggregateBarrier {
+ PoisonedHash() = delete;
+ PoisonedHash(const PoisonedHash&) = delete;
+ PoisonedHash& operator=(const PoisonedHash&) = delete;
+};
+
+template <typename T>
+struct HashImpl {
+ size_t operator()(const T& value) const { return CityHashState::hash(value); }
+};
+
+template <typename T>
+struct Hash
+ : absl::conditional_t<is_hashable<T>::value, HashImpl<T>, PoisonedHash> {};
+
+template <typename H>
+template <typename T, typename... Ts>
+H HashStateBase<H>::combine(H state, const T& value, const Ts&... values) {
+ return H::combine(hash_internal::InvokeHash(std::move(state), value),
+ values...);
+}
+
+// HashStateBase::combine_contiguous()
+template <typename H>
+template <typename T>
+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);
+}
+} // namespace hash_internal
+} // inline namespace lts_2018_12_18
+} // namespace absl
+
+#endif // ABSL_HASH_INTERNAL_HASH_H_