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1 //===--- AlignOf.h - Portable calculation of type alignment -----*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the AlignOf function that computes alignments for
11 // arbitrary types.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_SUPPORT_ALIGNOF_H
16 #define LLVM_SUPPORT_ALIGNOF_H
17 
18 namespace llvm {
19 
20 template <typename T>
21 struct AlignmentCalcImpl {
22   char x;
23   T t;
24 private:
AlignmentCalcImplAlignmentCalcImpl25   AlignmentCalcImpl() {} // Never instantiate.
26 };
27 
28 /// AlignOf - A templated class that contains an enum value representing
29 ///  the alignment of the template argument.  For example,
30 ///  AlignOf<int>::Alignment represents the alignment of type "int".  The
31 ///  alignment calculated is the minimum alignment, and not necessarily
32 ///  the "desired" alignment returned by GCC's __alignof__ (for example).  Note
33 ///  that because the alignment is an enum value, it can be used as a
34 ///  compile-time constant (e.g., for template instantiation).
35 template <typename T>
36 struct AlignOf {
37   enum { Alignment =
38          static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T)) };
39 
40   enum { Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0 };
41   enum { Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0 };
42   enum { Alignment_GreaterEqual_8Bytes = Alignment >= 8 ? 1 : 0 };
43   enum { Alignment_GreaterEqual_16Bytes = Alignment >= 16 ? 1 : 0 };
44 
45   enum { Alignment_LessEqual_2Bytes = Alignment <= 2 ? 1 : 0 };
46   enum { Alignment_LessEqual_4Bytes = Alignment <= 4 ? 1 : 0 };
47   enum { Alignment_LessEqual_8Bytes = Alignment <= 8 ? 1 : 0 };
48   enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 };
49 
50 };
51 
52 /// alignOf - A templated function that returns the minimum alignment of
53 ///  of a type.  This provides no extra functionality beyond the AlignOf
54 ///  class besides some cosmetic cleanliness.  Example usage:
55 ///  alignOf<int>() returns the alignment of an int.
56 template <typename T>
alignOf()57 static inline unsigned alignOf() { return AlignOf<T>::Alignment; }
58 
59 } // end namespace llvm
60 #endif
61