poco/Foundation/include/Poco/Alignment.h

//
// Alignment.h
//
// Library: Foundation
// Package: Dynamic
// Module:  Alignment
//
// Definition of the Alignment class.
//
// Copyright (c) 2007, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


// Adapted for POCO from LLVM Compiler Infrastructure code:
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source License
//
//===----------------------------------------------------------------------===//
//
// This file defines the AlignOf function that computes alignments for
// arbitrary types.
//
//===----------------------------------------------------------------------===//


#ifndef Foundation_AlignOf_INCLUDED
#define Foundation_AlignOf_INCLUDED


#include <cstddef>


#ifdef POCO_ENABLE_CPP11


	#include <type_traits>
	#define POCO_HAVE_ALIGNMENT


#else


	namespace Poco {


	template <typename T>
	struct AlignmentCalcImpl
	{
		char x;
		T t;
	private:
		AlignmentCalcImpl() {} // Never instantiate.
	};


	template <typename T>
	struct AlignOf
		/// A templated class that contains an enum value representing
		/// the alignment of the template argument.  For example,
		/// AlignOf<int>::Alignment represents the alignment of type "int".  The
		/// alignment calculated is the minimum alignment, and not necessarily
		/// the "desired" alignment returned by GCC's __alignof__ (for example).  Note
		/// that because the alignment is an enum value, it can be used as a
		/// compile-time constant (e.g., for template instantiation).
	{
		enum
		{
			Alignment = static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T))
		};

		enum { Alignment_GreaterEqual_2Bytes  = Alignment >= 2  ? 1 : 0 };
		enum { Alignment_GreaterEqual_4Bytes  = Alignment >= 4  ? 1 : 0 };
		enum { Alignment_GreaterEqual_8Bytes  = Alignment >= 8  ? 1 : 0 };
		enum { Alignment_GreaterEqual_16Bytes = Alignment >= 16 ? 1 : 0 };
	
		enum { Alignment_LessEqual_2Bytes  = Alignment <= 2  ? 1 : 0 };
		enum { Alignment_LessEqual_4Bytes  = Alignment <= 4  ? 1 : 0 };
		enum { Alignment_LessEqual_8Bytes  = Alignment <= 8  ? 1 : 0 };
		enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 };

	};


	template <typename T>
	inline unsigned alignOf()
		/// A templated function that returns the minimum alignment of
		/// of a type.  This provides no extra functionality beyond the AlignOf
		/// class besides some cosmetic cleanliness.  Example usage:
		/// alignOf<int>() returns the alignment of an int.
	{
		return AlignOf<T>::Alignment;
	}


	template <std::size_t Alignment> struct AlignedCharArrayImpl;
		/// Helper for building an aligned character array type.
		///
		/// This template is used to explicitly build up a collection of aligned
		/// character types. We have to build these up using a macro and explicit
		/// specialization to cope with old versions of MSVC and GCC where only an
		/// integer literal can be used to specify an alignment constraint. Once built
		/// up here, we can then begin to indirect between these using normal C++
		/// template parameters.


	// MSVC requires special handling here.
	#ifndef _MSC_VER

		#ifdef POCO_COMPILER_CLANG

			#if __has_feature(cxx_alignas)
				#define POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
					template <> struct AlignedCharArrayImpl<x> \
					{ \
						char aligned alignas(x); \
					}
				#define POCO_HAVE_ALIGNMENT
			#endif

		#elif defined(__GNUC__) || defined(__IBM_ATTRIBUTES)

			#define POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
				template <> struct AlignedCharArrayImpl<x> \
				{ \
					char aligned __attribute__((aligned(x))); \
				}
				#define POCO_HAVE_ALIGNMENT

		#endif
	
		#ifdef POCO_HAVE_ALIGNMENT
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(512);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1024);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2048);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4096);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8192);

			#undef POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
		#endif // POCO_HAVE_ALIGNMENT

	#else // _MSC_VER

		// We provide special variations of this template for the most common
		// alignments because __declspec(align(...)) doesn't actually work when it is
		// a member of a by-value function argument in MSVC, even if the alignment
		// request is something reasonably like 8-byte or 16-byte.
		template <> struct AlignedCharArrayImpl<1> { char aligned; };
		template <> struct AlignedCharArrayImpl<2> { short aligned; };
		template <> struct AlignedCharArrayImpl<4> { int aligned; };
		template <> struct AlignedCharArrayImpl<8> { double aligned; };

		#define POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
			template <> struct AlignedCharArrayImpl<x> { \
				__declspec(align(x)) char aligned; \
			}

		POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16);
		POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32);
		POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64);
		POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128);
		
		#if (_MSC_VER > 1600)  // MSVC 2010 complains on alignment  larger than 128
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(512);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1024);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2048);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4096);
			POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8192);
		#endif  // _MSC_VER > 1600
		
		// Any larger and MSVC complains.
		#undef POCO_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT

		#define POCO_HAVE_ALIGNMENT
	#endif // _MSC_VER

	// POCO_HAVE_ALIGNMENT will be defined on the pre-C++11 platforms/compilers where
	// it can be reliably determined and used. Uncomment the line below to explicitly
	// disable use of alignment even for those platforms. 
	// #undef POCO_HAVE_ALIGNMENT


	#ifdef POCO_HAVE_ALIGNMENT

		template <typename T1, typename T2 = char, typename T3 = char, typename T4 = char>
		union AlignedCharArrayUnion
			/// This union template exposes a suitably aligned and sized character
			/// array member which can hold elements of any of up to four types.
			///
			/// These types may be arrays, structs, or any other types. The goal is to
			/// produce a union type containing a character array which, when used, forms
			/// storage suitable to placement new any of these types over. Support for more
			/// than four types can be added at the cost of more boiler plate.
		{
		private:
			class AlignerImpl
			{
				T1 t1;
				T2 t2;
				T3 t3;
				T4 t4;
		
				AlignerImpl(); // Never defined or instantiated.
			};
	
			union SizerImpl
			{
				char arr1[sizeof(T1)];
				char arr2[sizeof(T2)];
				char arr3[sizeof(T3)];
				char arr4[sizeof(T4)];
			};
	
		public:
			char buffer[sizeof(SizerImpl)];
				/// The character array buffer for use by clients.
				///
				/// No other member of this union should be referenced. They exist purely to
				/// constrain the layout of this character array.
	
		private:
			Poco::AlignedCharArrayImpl<AlignOf<AlignerImpl>::Alignment> _nonceMember;

		};

	#endif // POCO_HAVE_ALIGNMENT

	} // namespace Poco


#endif // POCO_ENABLE_CPP11


#endif // Foundation_AlignOf_INCLUDED