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227 lines
5.9 KiB
C++
227 lines
5.9 KiB
C++
//
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// Alignment.h
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//
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// Library: Foundation
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// Package: Dynamic
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// Module: Alignment
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//
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// Definition of the Alignment class.
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//
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// Copyright (c) 2007, Applied Informatics Software Engineering GmbH.
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// and Contributors.
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//
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// SPDX-License-Identifier: BSL-1.0
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//
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// Adapted for POCO from LLVM Compiler Infrastructure code:
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source License
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the AlignOf function that computes alignments for
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// arbitrary types.
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//
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//===----------------------------------------------------------------------===//
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#ifndef Foundation_AlignOf_INCLUDED
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#define Foundation_AlignOf_INCLUDED
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#include <cstddef>
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#ifdef POCO_ENABLE_CPP11
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# include <type_traits>
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# define POCO_HAVE_ALIGNMENT
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#else
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namespace Poco
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{
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template <typename T>
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struct AlignmentCalcImpl
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{
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char x;
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T t;
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private:
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AlignmentCalcImpl() { } // Never instantiate.
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};
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template <typename T>
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struct AlignOf
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/// A templated class that contains an enum value representing
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/// the alignment of the template argument. For example,
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/// AlignOf<int>::Alignment represents the alignment of type "int". The
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/// alignment calculated is the minimum alignment, and not necessarily
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/// the "desired" alignment returned by GCC's __alignof__ (for example). Note
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/// that because the alignment is an enum value, it can be used as a
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/// compile-time constant (e.g., for template instantiation).
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{
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enum
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{
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Alignment = static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T))
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};
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enum
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{
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Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0
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};
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enum
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{
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Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0
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};
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enum
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{
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Alignment_GreaterEqual_8Bytes = Alignment >= 8 ? 1 : 0
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};
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enum
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{
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Alignment_GreaterEqual_16Bytes = Alignment >= 16 ? 1 : 0
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};
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enum
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{
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Alignment_LessEqual_2Bytes = Alignment <= 2 ? 1 : 0
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};
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enum
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{
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Alignment_LessEqual_4Bytes = Alignment <= 4 ? 1 : 0
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};
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enum
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{
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Alignment_LessEqual_8Bytes = Alignment <= 8 ? 1 : 0
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};
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enum
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{
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Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0
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};
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};
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template <typename T>
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inline unsigned alignOf()
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/// A templated function that returns the minimum alignment of
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/// of a type. This provides no extra functionality beyond the AlignOf
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/// class besides some cosmetic cleanliness. Example usage:
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/// alignOf<int>() returns the alignment of an int.
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{
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return AlignOf<T>::Alignment;
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}
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template <std::size_t Alignment>
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struct AlignedCharArrayImpl;
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/// Helper for building an aligned character array type.
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///
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/// This template is used to explicitly build up a collection of aligned
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/// character types. We have to build these up using a macro and explicit
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/// specialization to cope with old versions of MSVC and GCC where only an
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/// integer literal can be used to specify an alignment constraint. Once built
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/// up here, we can then begin to indirect between these using normal C++
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/// template parameters.
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// MSVC requires special handling here.
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# if __has_feature(cxx_alignas)
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# define POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
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template <> \
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struct AlignedCharArrayImpl<x> \
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{ \
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char aligned alignas(x); \
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}
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# define POCO_HAVE_ALIGNMENT
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# endif
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# ifdef POCO_HAVE_ALIGNMENT
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(512);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1024);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2048);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4096);
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POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8192);
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# undef POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
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# endif // POCO_HAVE_ALIGNMENT
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// POCO_HAVE_ALIGNMENT will be defined on the pre-C++11 platforms/compilers where
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// it can be reliably determined and used. Uncomment the line below to explicitly
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// disable use of alignment even for those platforms.
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// #undef POCO_HAVE_ALIGNMENT
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# ifdef POCO_HAVE_ALIGNMENT
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template <typename T1, typename T2 = char, typename T3 = char, typename T4 = char>
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union AlignedCharArrayUnion
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/// This union template exposes a suitably aligned and sized character
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/// array member which can hold elements of any of up to four types.
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///
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/// These types may be arrays, structs, or any other types. The goal is to
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/// produce a union type containing a character array which, when used, forms
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/// storage suitable to placement new any of these types over. Support for more
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/// than four types can be added at the cost of more boiler plate.
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{
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private:
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class AlignerImpl
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{
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T1 t1;
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T2 t2;
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T3 t3;
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T4 t4;
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AlignerImpl(); // Never defined or instantiated.
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};
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union SizerImpl
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{
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char arr1[sizeof(T1)];
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char arr2[sizeof(T2)];
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char arr3[sizeof(T3)];
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char arr4[sizeof(T4)];
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};
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public:
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char buffer[sizeof(SizerImpl)];
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/// The character array buffer for use by clients.
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///
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/// No other member of this union should be referenced. They exist purely to
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/// constrain the layout of this character array.
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private:
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Poco::AlignedCharArrayImpl<AlignOf<AlignerImpl>::Alignment> _nonceMember;
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};
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# endif // POCO_HAVE_ALIGNMENT
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} // namespace Poco
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#endif // POCO_ENABLE_CPP11
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#endif // Foundation_AlignOf_INCLUDED
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