98 lines
3.8 KiB
C
98 lines
3.8 KiB
C
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// Protocol Buffers - Google's data interchange format
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// Copyright 2008 Google Inc. All rights reserved.
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// https://developers.google.com/protocol-buffers/
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#ifndef GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__
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#define GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__
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#include <stdint.h>
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#include <utility>
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#include <google/protobuf/stubs/logging.h>
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#include <google/protobuf/stubs/common.h>
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// clang-format off
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#include <google/protobuf/port_def.inc>
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// clang-format on
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namespace google {
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namespace protobuf {
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namespace internal {
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// Wraps a variable whose constructor and destructor are explicitly
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// called. It is particularly useful for a global variable, without its
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// constructor and destructor run on start and end of the program lifetime.
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// This circumvents the initial construction order fiasco, while keeping
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// the address of the empty string a compile time constant.
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//
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// Pay special attention to the initialization state of the object.
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// 1. The object is "uninitialized" to begin with.
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// 2. Call Construct() or DefaultConstruct() only if the object is
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// uninitialized. After the call, the object becomes "initialized".
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// 3. Call get() and get_mutable() only if the object is initialized.
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// 4. Call Destruct() only if the object is initialized.
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// After the call, the object becomes uninitialized.
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template <typename T, size_t min_align = 1>
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class ExplicitlyConstructed {
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public:
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void DefaultConstruct() { new (&union_) T(); }
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template <typename... Args>
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void Construct(Args&&... args) {
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new (&union_) T(std::forward<Args>(args)...);
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}
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void Destruct() { get_mutable()->~T(); }
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constexpr const T& get() const { return reinterpret_cast<const T&>(union_); }
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T* get_mutable() { return reinterpret_cast<T*>(&union_); }
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private:
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union AlignedUnion {
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alignas(min_align > alignof(T) ? min_align
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: alignof(T)) char space[sizeof(T)];
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int64_t align_to_int64;
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void* align_to_ptr;
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} union_;
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};
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// ArenaStringPtr compatible explicitly constructed string type.
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// This empty string type is aligned with a minimum alignment of 8 bytes
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// which is the minimum requirement of ArenaStringPtr
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using ExplicitlyConstructedArenaString = ExplicitlyConstructed<std::string, 8>;
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} // namespace internal
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} // namespace protobuf
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} // namespace google
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#include <google/protobuf/port_undef.inc>
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#endif // GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__
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