ClickHouse/base/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.


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


// 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