include/android-base/macros.h - platform/system/libbase - Git at Google

 /*
  * Copyright (C) 2015 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #ifndef UTILS_MACROS_H
 #define UTILS_MACROS_H

 #include <stddef.h>  // for size_t
 #include <unistd.h>  // for TEMP_FAILURE_RETRY

 // bionic and glibc both have TEMP_FAILURE_RETRY, but eg Mac OS' libc doesn't.
 #ifndef TEMP_FAILURE_RETRY
 #define TEMP_FAILURE_RETRY(exp)            \
   ({                                       \
     decltype(exp) _rc;                     \
     do {                                   \
       _rc = (exp);                         \
     } while (_rc == -1 && errno == EINTR); \
     _rc;                                   \
   })
 #endif

 // A macro to disallow the copy constructor and operator= functions
 // This must be placed in the private: declarations for a class.
 //
 // For disallowing only assign or copy, delete the relevant operator or
 // constructor, for example:
 // void operator=(const TypeName&) = delete;
 // Note, that most uses of DISALLOW_ASSIGN and DISALLOW_COPY are broken
 // semantically, one should either use disallow both or neither. Try to
 // avoid these in new code.
 //
 // When building with C++11 toolchains, just use the language support
 // for explicitly deleted methods.
 #if __cplusplus >= 201103L
 #define DISALLOW_COPY_AND_ASSIGN(TypeName) \
   TypeName(const TypeName&) = delete;      \
   void operator=(const TypeName&) = delete
 #else
 #define DISALLOW_COPY_AND_ASSIGN(TypeName) \
   TypeName(const TypeName&);               \
   void operator=(const TypeName&)
 #endif

 // A macro to disallow all the implicit constructors, namely the
 // default constructor, copy constructor and operator= functions.
 //
 // This should be used in the private: declarations for a class
 // that wants to prevent anyone from instantiating it. This is
 // especially useful for classes containing only static methods.
 #define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
   TypeName();                                    \
   DISALLOW_COPY_AND_ASSIGN(TypeName)

 // The arraysize(arr) macro returns the # of elements in an array arr.
 // The expression is a compile-time constant, and therefore can be
 // used in defining new arrays, for example.  If you use arraysize on
 // a pointer by mistake, you will get a compile-time error.
 //
 // One caveat is that arraysize() doesn't accept any array of an
 // anonymous type or a type defined inside a function.  In these rare
 // cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below.  This is
 // due to a limitation in C++'s template system.  The limitation might
 // eventually be removed, but it hasn't happened yet.

 // This template function declaration is used in defining arraysize.
 // Note that the function doesn't need an implementation, as we only
 // use its type.
 template <typename T, size_t N>
 char(&ArraySizeHelper(T(&array)[N]))[N];  // NOLINT(readability/casting)

 #define arraysize(array) (sizeof(ArraySizeHelper(array)))

 // ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize,
 // but can be used on anonymous types or types defined inside
 // functions.  It's less safe than arraysize as it accepts some
 // (although not all) pointers.  Therefore, you should use arraysize
 // whenever possible.
 //
 // The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type
 // size_t.
 //
 // ARRAYSIZE_UNSAFE catches a few type errors.  If you see a compiler error
 //
 //   "warning: division by zero in ..."
 //
 // when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer.
 // You should only use ARRAYSIZE_UNSAFE on statically allocated arrays.
 //
 // The following comments are on the implementation details, and can
 // be ignored by the users.
 //
 // ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in
 // the array) and sizeof(*(arr)) (the # of bytes in one array
 // element).  If the former is divisible by the latter, perhaps arr is
 // indeed an array, in which case the division result is the # of
 // elements in the array.  Otherwise, arr cannot possibly be an array,
 // and we generate a compiler error to prevent the code from
 // compiling.
 //
 // Since the size of bool is implementation-defined, we need to cast
 // !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final
 // result has type size_t.
 //
 // This macro is not perfect as it wrongfully accepts certain
 // pointers, namely where the pointer size is divisible by the pointee
 // size.  Since all our code has to go through a 32-bit compiler,
 // where a pointer is 4 bytes, this means all pointers to a type whose
 // size is 3 or greater than 4 will be (righteously) rejected.
 #define ARRAYSIZE_UNSAFE(a)     \
   ((sizeof(a) / sizeof(*(a))) / \
     static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))

 #define LIKELY(x) __builtin_expect((x), true)
 #define UNLIKELY(x) __builtin_expect((x), false)

 #define WARN_UNUSED __attribute__((warn_unused_result))

 // A deprecated function to call to create a false use of the parameter, for
 // example:
 //   int foo(int x) { UNUSED(x); return 10; }
 // to avoid compiler warnings. Going forward we prefer ATTRIBUTE_UNUSED.
 template <typename... T>
 void UNUSED(const T&...) {
 }

 // An attribute to place on a parameter to a function, for example:
 //   int foo(int x ATTRIBUTE_UNUSED) { return 10; }
 // to avoid compiler warnings.
 #define ATTRIBUTE_UNUSED __attribute__((__unused__))

 // The FALLTHROUGH_INTENDED macro can be used to annotate implicit fall-through
 // between switch labels:
 //  switch (x) {
 //    case 40:
 //    case 41:
 //      if (truth_is_out_there) {
 //        ++x;
 //        FALLTHROUGH_INTENDED;  // Use instead of/along with annotations in
 //                               // comments.
 //      } else {
 //        return x;
 //      }
 //    case 42:
 //      ...
 //
 //  As shown in the example above, the FALLTHROUGH_INTENDED macro should be
 //  followed by a semicolon. It is designed to mimic control-flow statements
 //  like 'break;', so it can be placed in most places where 'break;' can, but
 //  only if there are no statements on the execution path between it and the
 //  next switch label.
 //
 //  When compiled with clang in C++11 mode, the FALLTHROUGH_INTENDED macro is
 //  expanded to [[clang::fallthrough]] attribute, which is analysed when
 //  performing switch labels fall-through diagnostic ('-Wimplicit-fallthrough').
 //  See clang documentation on language extensions for details:
 //  http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough
 //
 //  When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no
 //  effect on diagnostics.
 //
 //  In either case this macro has no effect on runtime behavior and performance
 //  of code.
 #if defined(__clang__) && __cplusplus >= 201103L && defined(__has_warning)
 #if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough")
 #define FALLTHROUGH_INTENDED [[clang::fallthrough]]  // NOLINT
 #endif
 #endif

 #ifndef FALLTHROUGH_INTENDED
 #define FALLTHROUGH_INTENDED \
   do {                       \
   } while (0)
 #endif

 #endif  // UTILS_MACROS_H
	/*
	* Copyright (C) 2015 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#ifndef UTILS_MACROS_H
	#define UTILS_MACROS_H

	#include <stddef.h> // for size_t
	#include <unistd.h> // for TEMP_FAILURE_RETRY

	// bionic and glibc both have TEMP_FAILURE_RETRY, but eg Mac OS' libc doesn't.
	#ifndef TEMP_FAILURE_RETRY
	#define TEMP_FAILURE_RETRY(exp) \
	({ \
	decltype(exp) _rc; \
	do { \
	_rc = (exp); \
	} while (_rc == -1 && errno == EINTR); \
	_rc; \
	})
	#endif

	// A macro to disallow the copy constructor and operator= functions
	// This must be placed in the private: declarations for a class.
	//
	// For disallowing only assign or copy, delete the relevant operator or
	// constructor, for example:
	// void operator=(const TypeName&) = delete;
	// Note, that most uses of DISALLOW_ASSIGN and DISALLOW_COPY are broken
	// semantically, one should either use disallow both or neither. Try to
	// avoid these in new code.
	//
	// When building with C++11 toolchains, just use the language support
	// for explicitly deleted methods.
	#if __cplusplus >= 201103L
	#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
	TypeName(const TypeName&) = delete; \
	void operator=(const TypeName&) = delete
	#else
	#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
	TypeName(const TypeName&); \
	void operator=(const TypeName&)
	#endif

	// A macro to disallow all the implicit constructors, namely the
	// default constructor, copy constructor and operator= functions.
	//
	// This should be used in the private: declarations for a class
	// that wants to prevent anyone from instantiating it. This is
	// especially useful for classes containing only static methods.
	#define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
	TypeName(); \
	DISALLOW_COPY_AND_ASSIGN(TypeName)

	// The arraysize(arr) macro returns the # of elements in an array arr.
	// The expression is a compile-time constant, and therefore can be
	// used in defining new arrays, for example. If you use arraysize on
	// a pointer by mistake, you will get a compile-time error.
	//
	// One caveat is that arraysize() doesn't accept any array of an
	// anonymous type or a type defined inside a function. In these rare
	// cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below. This is
	// due to a limitation in C++'s template system. The limitation might
	// eventually be removed, but it hasn't happened yet.

	// This template function declaration is used in defining arraysize.
	// Note that the function doesn't need an implementation, as we only
	// use its type.
	template <typename T, size_t N>
	char(&ArraySizeHelper(T(&array)[N]))[N]; // NOLINT(readability/casting)

	#define arraysize(array) (sizeof(ArraySizeHelper(array)))

	// ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize,
	// but can be used on anonymous types or types defined inside
	// functions. It's less safe than arraysize as it accepts some
	// (although not all) pointers. Therefore, you should use arraysize
	// whenever possible.
	//
	// The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type
	// size_t.
	//
	// ARRAYSIZE_UNSAFE catches a few type errors. If you see a compiler error
	//
	// "warning: division by zero in ..."
	//
	// when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer.
	// You should only use ARRAYSIZE_UNSAFE on statically allocated arrays.
	//
	// The following comments are on the implementation details, and can
	// be ignored by the users.
	//
	// ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in
	// the array) and sizeof(*(arr)) (the # of bytes in one array
	// element). If the former is divisible by the latter, perhaps arr is
	// indeed an array, in which case the division result is the # of
	// elements in the array. Otherwise, arr cannot possibly be an array,
	// and we generate a compiler error to prevent the code from
	// compiling.
	//
	// Since the size of bool is implementation-defined, we need to cast
	// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final
	// result has type size_t.
	//
	// This macro is not perfect as it wrongfully accepts certain
	// pointers, namely where the pointer size is divisible by the pointee
	// size. Since all our code has to go through a 32-bit compiler,
	// where a pointer is 4 bytes, this means all pointers to a type whose
	// size is 3 or greater than 4 will be (righteously) rejected.
	#define ARRAYSIZE_UNSAFE(a) \
	((sizeof(a) / sizeof(*(a))) / \
	static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))

	#define LIKELY(x) __builtin_expect((x), true)
	#define UNLIKELY(x) __builtin_expect((x), false)

	#define WARN_UNUSED __attribute__((warn_unused_result))

	// A deprecated function to call to create a false use of the parameter, for
	// example:
	// int foo(int x) { UNUSED(x); return 10; }
	// to avoid compiler warnings. Going forward we prefer ATTRIBUTE_UNUSED.
	template <typename... T>
	void UNUSED(const T&...) {
	}

	// An attribute to place on a parameter to a function, for example:
	// int foo(int x ATTRIBUTE_UNUSED) { return 10; }
	// to avoid compiler warnings.
	#define ATTRIBUTE_UNUSED __attribute__((__unused__))

	// The FALLTHROUGH_INTENDED macro can be used to annotate implicit fall-through
	// between switch labels:
	// switch (x) {
	// case 40:
	// case 41:
	// if (truth_is_out_there) {
	// ++x;
	// FALLTHROUGH_INTENDED; // Use instead of/along with annotations in
	// // comments.
	// } else {
	// return x;
	// }
	// case 42:
	// ...
	//
	// As shown in the example above, the FALLTHROUGH_INTENDED macro should be
	// followed by a semicolon. It is designed to mimic control-flow statements
	// like 'break;', so it can be placed in most places where 'break;' can, but
	// only if there are no statements on the execution path between it and the
	// next switch label.
	//
	// When compiled with clang in C++11 mode, the FALLTHROUGH_INTENDED macro is
	// expanded to [[clang::fallthrough]] attribute, which is analysed when
	// performing switch labels fall-through diagnostic ('-Wimplicit-fallthrough').
	// See clang documentation on language extensions for details:
	// http://clang.llvm.org/docs/LanguageExtensions.html#clang__fallthrough
	//
	// When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no
	// effect on diagnostics.
	//
	// In either case this macro has no effect on runtime behavior and performance
	// of code.
	#if defined(__clang__) && __cplusplus >= 201103L && defined(__has_warning)
	#if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough")
	#define FALLTHROUGH_INTENDED [[clang::fallthrough]] // NOLINT
	#endif
	#endif

	#ifndef FALLTHROUGH_INTENDED
	#define FALLTHROUGH_INTENDED \
	do { \
	} while (0)
	#endif

	#endif // UTILS_MACROS_H