c/system/macros.h

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MOJO_PUBLIC_C_SYSTEM_MACROS_H_
#define MOJO_PUBLIC_C_SYSTEM_MACROS_H_

#include <stddef.h>

// Annotate a variable indicating it's okay if it's unused.
// Use like:
//   int x = ...;
//   MOJO_ALLOW_UNUSED_LOCAL(x);
#define MOJO_ALLOW_UNUSED_LOCAL(x) false ? (void)x : (void)0

// Annotate a function indicating that the caller must examine the return value.
// Use like:
//   int foo() MOJO_WARN_UNUSED_RESULT;
// Note that it can only be used on the prototype, and not the definition.
#if defined(__GNUC__)
#define MOJO_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
#else
#define MOJO_WARN_UNUSED_RESULT
#endif

// Assert things at compile time. (|msg| should be a valid identifier name.)
// Use like:
//   MOJO_STATIC_ASSERT(sizeof(Foo) == 12, "Foo has invalid size");
#if defined(__cplusplus)
#define MOJO_STATIC_ASSERT(expr, msg) static_assert(expr, msg)
#else
#define MOJO_STATIC_ASSERT(expr, msg) _Static_assert(expr, msg)
#endif

// Like the C++11 |alignof| operator.
#if defined(__cplusplus) && __cplusplus >= 201103L
#define MOJO_ALIGNOF(type) alignof(type)
#elif defined(__GNUC__)
#define MOJO_ALIGNOF(type) __alignof__(type)
#elif defined(_MSC_VER)
// The use of |sizeof| is to work around a bug in MSVC 2010 (see
// http://goo.gl/isH0C; supposedly fixed since then).
#define MOJO_ALIGNOF(type) (sizeof(type) - sizeof(type) + __alignof(type))
#else
#error "Please define MOJO_ALIGNOF() for your compiler."
#endif

// Specify the alignment of a |struct|, etc.
// Use like:
//   struct MOJO_ALIGNAS(8) Foo { ... };
// Unlike the C++11 |alignas()|, |alignment| must be an integer. It may not be a
// type, nor can it be an expression like |MOJO_ALIGNOF(type)| (due to the
// non-C++11 MSVS version).
#if defined(__cplusplus) && __cplusplus >= 201103L
#define MOJO_ALIGNAS(alignment) alignas(alignment)
#elif defined(__GNUC__)
#define MOJO_ALIGNAS(alignment) __attribute__((aligned(alignment)))
#elif defined(_MSC_VER)
#define MOJO_ALIGNAS(alignment) __declspec(align(alignment))
#else
#error "Please define MOJO_ALIGNAS() for your compiler."
#endif

// Use these to declare functions in C header files so that they'll be usable
// from C++.
#if defined(__cplusplus)
#define MOJO_BEGIN_EXTERN_C extern "C" {
#define MOJO_END_EXTERN_C }
#else
#define MOJO_BEGIN_EXTERN_C
#define MOJO_END_EXTERN_C
#endif

// Use |MOJO_RESTRICT| (in C function declarations) in place of C99's
// |restrict|, to work properly with C++. (It allows certain optimizations, but
// more importantly it serves a documentary purpose for the caller.)
//
// Recommendation: If a function has multiple pointer parameters at least one of
// which is to non-const, then all the pointer parameters should be declared
// using |MOJO_RESTRICT| unless aliasing is explicitly allowed.
#if defined(__GNUC__) || defined(_MSC_VER)
// Use |__restrict|, since it works both in C++ and when compiling as C90
// (|restrict| is only available in C99 and later, and never in C++).
#define MOJO_RESTRICT __restrict
#else
#error "Please define MOJO_RESTRICT for your compiler."
#endif

#endif  // MOJO_PUBLIC_C_SYSTEM_MACROS_H_