text: //===--- AlignOf.h - Portable calculation of type alignment -----*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file defines the AlignOf function that computes alignments for
  // arbitrary types.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_SUPPORT_ALIGNOF_H
  #define LLVM_SUPPORT_ALIGNOF_H
  
  #include "llvm/Support/Compiler.h"
  #include <cstddef>
  
  namespace llvm {
  template <typename T>
  struct AlignmentCalcImpl {
    char x;
    T t;
  private:
    AlignmentCalcImpl() {} // Never instantiate.
  };
  
  /// 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).
  template <typename T>
  struct AlignOf {
    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 };
  };
  
  /// 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.
  template <typename T>
  inline unsigned alignOf() { return AlignOf<T>::Alignment; }
  
  /// \struct AlignedCharArray
  /// \brief Helper for building an aligned character array type.
  ///
  /// This template is used to explicitly build up a collection of aligned
  /// character array 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
  
  #if __has_feature(cxx_alignas)
  template<std::size_t Alignment, std::size_t Size>
  struct AlignedCharArray {
    alignas(Alignment) char buffer[Size];
  };
  
  #elif defined(__GNUC__) || defined(__IBM_ATTRIBUTES)
  /// \brief Create a type with an aligned char buffer.
  template<std::size_t Alignment, std::size_t Size>
  struct AlignedCharArray;
  
  #define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
    template<std::size_t Size> \
    struct AlignedCharArray<x, Size> { \
      __attribute__((aligned(x))) char buffer[Size]; \
    };
  
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
  
  #undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
  
  #else
  # error No supported align as directive.
  #endif
  
  #else // _MSC_VER
  
  /// \brief Create a type with an aligned char buffer.
  template<std::size_t Alignment, std::size_t Size>
  struct AlignedCharArray;
  
  // 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. Note that we can't
  // even include the declspec with the union that forces the alignment because
  // MSVC warns on the existence of the declspec despite the union member forcing
  // proper alignment.
  
  template<std::size_t Size>
  struct AlignedCharArray<1, Size> {
    union {
      char aligned;
      char buffer[Size];
    };
  };
  
  template<std::size_t Size>
  struct AlignedCharArray<2, Size> {
    union {
      short aligned;
      char buffer[Size];
    };
  };
  
  template<std::size_t Size>
  struct AlignedCharArray<4, Size> {
    union {
      int aligned;
      char buffer[Size];
    };
  };
  
  template<std::size_t Size>
  struct AlignedCharArray<8, Size> {
    union {
      double aligned;
      char buffer[Size];
    };
  };
  
  
  // The rest of these are provided with a __declspec(align(...)) and we simply
  // can't pass them by-value as function arguments on MSVC.
  
  #define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
    template<std::size_t Size> \
    struct AlignedCharArray<x, Size> { \
      __declspec(align(x)) char buffer[Size]; \
    };
  
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64)
  LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
  
  #undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
  
  #endif // _MSC_VER
  
  namespace detail {
  template <typename T1,
            typename T2 = char, typename T3 = char, typename T4 = char,
            typename T5 = char, typename T6 = char, typename T7 = char,
            typename T8 = char, typename T9 = char, typename T10 = char>
  class AlignerImpl {
    T1 t1; T2 t2; T3 t3; T4 t4; T5 t5; T6 t6; T7 t7; T8 t8; T9 t9; T10 t10;
  
    AlignerImpl(); // Never defined or instantiated.
  };
  
  template <typename T1,
            typename T2 = char, typename T3 = char, typename T4 = char,
            typename T5 = char, typename T6 = char, typename T7 = char,
            typename T8 = char, typename T9 = char, typename T10 = char>
  union SizerImpl {
    char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)],
         arr5[sizeof(T5)], arr6[sizeof(T6)], arr7[sizeof(T7)], arr8[sizeof(T8)],
         arr9[sizeof(T9)], arr10[sizeof(T10)];
  };
  } // end namespace detail
  
  /// \brief 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
  /// expose a char array buffer member which can be used as suitable storage for
  /// a placement new of any of these types. Support for more than seven types can
  /// be added at the cost of more boiler plate.
  template <typename T1,
            typename T2 = char, typename T3 = char, typename T4 = char,
            typename T5 = char, typename T6 = char, typename T7 = char,
            typename T8 = char, typename T9 = char, typename T10 = char>
  struct AlignedCharArrayUnion : llvm::AlignedCharArray<
      AlignOf<detail::AlignerImpl<T1, T2, T3, T4, T5,
                                  T6, T7, T8, T9, T10> >::Alignment,
      sizeof(detail::SizerImpl<T1, T2, T3, T4, T5,
                               T6, T7, T8, T9, T10>)> {
  };
  } // end namespace llvm
  #endif
  