llvm-mirror/include/llvm/Support/AlignOf.h

//===--- 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

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>
static inline unsigned alignOf() { return AlignOf<T>::Alignment; }

} // end namespace llvm
#endif