1 /* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef ANDROID_BASE_MACROS_H 18 #define ANDROID_BASE_MACROS_H 19 20 #include <stddef.h> // for size_t 21 #include <unistd.h> // for TEMP_FAILURE_RETRY 22 23 // bionic and glibc both have TEMP_FAILURE_RETRY, but eg Mac OS' libc doesn't. 24 #ifndef TEMP_FAILURE_RETRY 25 #define TEMP_FAILURE_RETRY(exp) \ 26 ({ \ 27 decltype(exp) _rc; \ 28 do { \ 29 _rc = (exp); \ 30 } while (_rc == -1 && errno == EINTR); \ 31 _rc; \ 32 }) 33 #endif 34 35 // A macro to disallow the copy constructor and operator= functions 36 // This must be placed in the private: declarations for a class. 37 // 38 // For disallowing only assign or copy, delete the relevant operator or 39 // constructor, for example: 40 // void operator=(const TypeName&) = delete; 41 // Note, that most uses of DISALLOW_ASSIGN and DISALLOW_COPY are broken 42 // semantically, one should either use disallow both or neither. Try to 43 // avoid these in new code. 44 #define DISALLOW_COPY_AND_ASSIGN(TypeName) \ 45 TypeName(const TypeName&) = delete; \ 46 void operator=(const TypeName&) = delete 47 48 // A macro to disallow all the implicit constructors, namely the 49 // default constructor, copy constructor and operator= functions. 50 // 51 // This should be used in the private: declarations for a class 52 // that wants to prevent anyone from instantiating it. This is 53 // especially useful for classes containing only static methods. 54 #define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \ 55 TypeName() = delete; \ 56 DISALLOW_COPY_AND_ASSIGN(TypeName) 57 58 // The arraysize(arr) macro returns the # of elements in an array arr. 59 // The expression is a compile-time constant, and therefore can be 60 // used in defining new arrays, for example. If you use arraysize on 61 // a pointer by mistake, you will get a compile-time error. 62 // 63 // One caveat is that arraysize() doesn't accept any array of an 64 // anonymous type or a type defined inside a function. In these rare 65 // cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below. This is 66 // due to a limitation in C++'s template system. The limitation might 67 // eventually be removed, but it hasn't happened yet. 68 69 // This template function declaration is used in defining arraysize. 70 // Note that the function doesn't need an implementation, as we only 71 // use its type. 72 template <typename T, size_t N> 73 char(&ArraySizeHelper(T(&array)[N]))[N]; // NOLINT(readability/casting) 74 75 #define arraysize(array) (sizeof(ArraySizeHelper(array))) 76 77 // ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize, 78 // but can be used on anonymous types or types defined inside 79 // functions. It's less safe than arraysize as it accepts some 80 // (although not all) pointers. Therefore, you should use arraysize 81 // whenever possible. 82 // 83 // The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type 84 // size_t. 85 // 86 // ARRAYSIZE_UNSAFE catches a few type errors. If you see a compiler error 87 // 88 // "warning: division by zero in ..." 89 // 90 // when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer. 91 // You should only use ARRAYSIZE_UNSAFE on statically allocated arrays. 92 // 93 // The following comments are on the implementation details, and can 94 // be ignored by the users. 95 // 96 // ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in 97 // the array) and sizeof(*(arr)) (the # of bytes in one array 98 // element). If the former is divisible by the latter, perhaps arr is 99 // indeed an array, in which case the division result is the # of 100 // elements in the array. Otherwise, arr cannot possibly be an array, 101 // and we generate a compiler error to prevent the code from 102 // compiling. 103 // 104 // Since the size of bool is implementation-defined, we need to cast 105 // !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final 106 // result has type size_t. 107 // 108 // This macro is not perfect as it wrongfully accepts certain 109 // pointers, namely where the pointer size is divisible by the pointee 110 // size. Since all our code has to go through a 32-bit compiler, 111 // where a pointer is 4 bytes, this means all pointers to a type whose 112 // size is 3 or greater than 4 will be (righteously) rejected. 113 #define ARRAYSIZE_UNSAFE(a) \ 114 ((sizeof(a) / sizeof(*(a))) / \ 115 static_cast<size_t>(!(sizeof(a) % sizeof(*(a))))) 116 117 // Changing this definition will cause you a lot of pain. A majority of 118 // vendor code defines LIKELY and UNLIKELY this way, and includes 119 // this header through an indirect path. 120 #define LIKELY( exp ) (__builtin_expect( (exp) != 0, true )) 121 #define UNLIKELY( exp ) (__builtin_expect( (exp) != 0, false )) 122 123 #define WARN_UNUSED __attribute__((warn_unused_result)) 124 125 // A deprecated function to call to create a false use of the parameter, for 126 // example: 127 // int foo(int x) { UNUSED(x); return 10; } 128 // to avoid compiler warnings. Going forward we prefer ATTRIBUTE_UNUSED. 129 template <typename... T> 130 void UNUSED(const T&...) { 131 } 132 133 // An attribute to place on a parameter to a function, for example: 134 // int foo(int x ATTRIBUTE_UNUSED) { return 10; } 135 // to avoid compiler warnings. 136 #define ATTRIBUTE_UNUSED __attribute__((__unused__)) 137 138 // The FALLTHROUGH_INTENDED macro can be used to annotate implicit fall-through 139 // between switch labels: 140 // switch (x) { 141 // case 40: 142 // case 41: 143 // if (truth_is_out_there) { 144 // ++x; 145 // FALLTHROUGH_INTENDED; // Use instead of/along with annotations in 146 // // comments. 147 // } else { 148 // return x; 149 // } 150 // case 42: 151 // ... 152 // 153 // As shown in the example above, the FALLTHROUGH_INTENDED macro should be 154 // followed by a semicolon. It is designed to mimic control-flow statements 155 // like 'break;', so it can be placed in most places where 'break;' can, but 156 // only if there are no statements on the execution path between it and the 157 // next switch label. 158 // 159 // When compiled with clang, the FALLTHROUGH_INTENDED macro is expanded to 160 // [[clang::fallthrough]] attribute, which is analysed when performing switch 161 // labels fall-through diagnostic ('-Wimplicit-fallthrough'). See clang 162 // documentation on language extensions for details: 163 // http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough 164 // 165 // When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no 166 // effect on diagnostics. 167 // 168 // In either case this macro has no effect on runtime behavior and performance 169 // of code. 170 #if defined(__clang__) && defined(__has_warning) 171 #if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough") 172 #define FALLTHROUGH_INTENDED [[clang::fallthrough]] // NOLINT 173 #endif 174 #endif 175 176 #ifndef FALLTHROUGH_INTENDED 177 #define FALLTHROUGH_INTENDED \ 178 do { \ 179 } while (0) 180 #endif 181 182 // Current ABI string 183 #if defined(__arm__) 184 #define ABI_STRING "arm" 185 #elif defined(__aarch64__) 186 #define ABI_STRING "arm64" 187 #elif defined(__i386__) 188 #define ABI_STRING "x86" 189 #elif defined(__x86_64__) 190 #define ABI_STRING "x86_64" 191 #elif defined(__mips__) && !defined(__LP64__) 192 #define ABI_STRING "mips" 193 #elif defined(__mips__) && defined(__LP64__) 194 #define ABI_STRING "mips64" 195 #endif 196 197 #endif // ANDROID_BASE_MACROS_H 198
