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: 25 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> 57 static inline unsigned alignOf() { return AlignOf<T>::Alignment; } 58 59 } // end namespace llvm 60 #endif 61
