95 lines
3.4 KiB
C++
95 lines
3.4 KiB
C++
/*
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* FileIdentifier.h
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*
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* This source file is part of the FoundationDB open source project
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*
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* Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <cstdint>
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#include <type_traits>
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using FileIdentifier = uint32_t;
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struct Empty {};
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template <typename T, typename = int>
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struct HasFileIdentifierMember : std::false_type {};
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template <typename T>
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struct HasFileIdentifierMember<T, decltype((void)T::file_identifier, 0)> : std::true_type {};
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template <typename T, typename = int>
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struct CompositionDepthFor : std::integral_constant<int, 0> {};
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template <typename T>
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struct CompositionDepthFor<T, decltype((void)T::composition_depth, 0)>
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: std::integral_constant<int, T::composition_depth> {};
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template <class T, bool>
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struct FileIdentifierForBase;
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template <class T>
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struct FileIdentifierForBase<T, false> {};
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template <class T>
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struct FileIdentifierForBase<T, true> {
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static constexpr FileIdentifier value = T::file_identifier;
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static_assert(CompositionDepthFor<T>::value > 0 || T::file_identifier < (1 << 24),
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"non-composed file identifiers must be less than 2^24");
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};
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template <class T>
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struct FileIdentifierFor : FileIdentifierForBase<T, HasFileIdentifierMember<T>::value> {};
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template <typename T, typename = int>
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struct HasFileIdentifier : std::false_type {};
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template <typename T>
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struct HasFileIdentifier<T, decltype((void)FileIdentifierFor<T>::value, 0)> : std::true_type {};
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template <class T, uint8_t B, bool = (HasFileIdentifier<T>::value && CompositionDepthFor<T>::value < 2)>
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struct ComposedIdentifier;
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// Manually specified file identifiers must be less than 2^24.
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// The first 8 bits are used to identify the wrapper classes:
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// The 5th-8th bits represent the inner wrapper class
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// The 1st-4th bits represent the outer wrapper class
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// Types with more than two level of composition do not get file identifiers.
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template <class T, uint8_t B>
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struct ComposedIdentifier<T, B, true> {
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static_assert(CompositionDepthFor<T>::value < 2);
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static constexpr int composed_identifier_offset = (CompositionDepthFor<T>::value == 1) ? 28 : 24;
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static_assert(B > 0 && B < 16, "Up to 15 types of composed identifiers allowed");
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static_assert(FileIdentifierFor<T>::value < (1 << composed_identifier_offset));
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public:
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static constexpr int composition_depth = CompositionDepthFor<T>::value + 1;
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static constexpr FileIdentifier file_identifier = (B << composed_identifier_offset) | FileIdentifierFor<T>::value;
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};
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template <class T, uint8_t B>
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struct ComposedIdentifier<T, B, false> {};
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template <class T, uint32_t B, bool = HasFileIdentifier<T>::value>
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struct ComposedIdentifierExternal;
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template <class T, uint32_t B>
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struct ComposedIdentifierExternal<T, B, false> {};
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template <class T, uint32_t B>
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struct ComposedIdentifierExternal<T, B, true> {
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static constexpr FileIdentifier value = ComposedIdentifier<T, B>::file_identifier;
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};
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