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// Copyright 2014 the V8 project 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 V8_BASE_MACROS_H_
#define V8_BASE_MACROS_H_
#include "src/base/compiler-specific.h"
#include "src/base/format-macros.h"
#include "src/base/logging.h"
// TODO(all) Replace all uses of this macro with C++'s offsetof. To do that, we
// have to make sure that only standard-layout types and simple field
// designators are used.
#define OFFSET_OF(type, field) \
(reinterpret_cast<intptr_t>(&(reinterpret_cast<type*>(16)->field)) - 16)
// 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.
#define arraysize(array) (sizeof(ArraySizeHelper(array)))
// 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];
#if !V8_CC_MSVC
// That gcc wants both of these prototypes seems mysterious. VC, for
// its part, can't decide which to use (another mystery). Matching of
// template overloads: the final frontier.
template <typename T, size_t N>
char (&ArraySizeHelper(const T (&array)[N]))[N];
// bit_cast<Dest,Source> is a template function that implements the
// equivalent of "*reinterpret_cast<Dest*>(&source)". We need this in
// very low-level functions like the protobuf library and fast math
// support.
// float f = 3.14159265358979;
// int i = bit_cast<int32>(f);
// // i = 0x40490fdb
// The classical address-casting method is:
// // WRONG
// float f = 3.14159265358979; // WRONG
// int i = * reinterpret_cast<int*>(&f); // WRONG
// The address-casting method actually produces undefined behavior
// according to ISO C++ specification section 3.10 -15 -. Roughly, this
// section says: if an object in memory has one type, and a program
// accesses it with a different type, then the result is undefined
// behavior for most values of "different type".
// This is true for any cast syntax, either *(int*)&f or
// *reinterpret_cast<int*>(&f). And it is particularly true for
// conversions between integral lvalues and floating-point lvalues.
// The purpose of 3.10 -15- is to allow optimizing compilers to assume
// that expressions with different types refer to different memory. gcc
// 4.0.1 has an optimizer that takes advantage of this. So a
// non-conforming program quietly produces wildly incorrect output.
// The problem is not the use of reinterpret_cast. The problem is type
// punning: holding an object in memory of one type and reading its bits
// back using a different type.
// The C++ standard is more subtle and complex than this, but that
// is the basic idea.
// Anyways ...
// bit_cast<> calls memcpy() which is blessed by the standard,
// especially by the example in section 3.9 . Also, of course,
// bit_cast<> wraps up the nasty logic in one place.
// Fortunately memcpy() is very fast. In optimized mode, with a
// constant size, gcc 2.95.3, gcc 4.0.1, and msvc 7.1 produce inline
// code with the minimal amount of data movement. On a 32-bit system,
// memcpy(d,s,4) compiles to one load and one store, and memcpy(d,s,8)
// compiles to two loads and two stores.
// I tested this code with gcc 2.95.3, gcc 4.0.1, icc 8.1, and msvc 7.1.
// WARNING: if Dest or Source is a non-POD type, the result of the memcpy
// is likely to surprise you.
template <class Dest, class Source>
V8_INLINE Dest bit_cast(Source const& source) {
static_assert(sizeof(Dest) == sizeof(Source),
"source and dest must be same size");
Dest dest;
memcpy(&dest, &source, sizeof(dest));
return dest;
// Put this in the private: declarations for a class to be unassignable.
#define DISALLOW_ASSIGN(TypeName) void operator=(const TypeName&)
// A macro to disallow the evil copy constructor and operator= functions
// This should be used in the private: declarations for a class
TypeName(const TypeName&) = delete; \
void operator=(const TypeName&) = delete
// 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.
TypeName() = delete; \
// Newly written code should use V8_INLINE and V8_NOINLINE directly.
#define INLINE(declarator) V8_INLINE declarator
#define NO_INLINE(declarator) V8_NOINLINE declarator
// Newly written code should use WARN_UNUSED_RESULT.
// Define V8_USE_ADDRESS_SANITIZER macros.
#if defined(__has_feature)
#if __has_feature(address_sanitizer)
// Define DISABLE_ASAN macros.
#define DISABLE_ASAN __attribute__((no_sanitize_address))
#if V8_CC_GNU
#define V8_IMMEDIATE_CRASH() __builtin_trap()
#define V8_IMMEDIATE_CRASH() ((void(*)())0)()
// TODO(all) Replace all uses of this macro with static_assert, remove macro.
#define STATIC_ASSERT(test) static_assert(test, #test)
// The USE(x) template is used to silence C++ compiler warnings
// issued for (yet) unused variables (typically parameters).
template <typename T>
inline void USE(T) { }
#define IS_POWER_OF_TWO(x) ((x) != 0 && (((x) & ((x) - 1)) == 0))
// Define our own macros for writing 64-bit constants. This is less fragile
// than defining __STDC_CONSTANT_MACROS before including <stdint.h>, and it
// works on compilers that don't have it (like MSVC).
#if V8_CC_MSVC
# define V8_UINT64_C(x) (x ## UI64)
# define V8_INT64_C(x) (x ## I64)
# if V8_HOST_ARCH_64_BIT
# define V8_INTPTR_C(x) (x ## I64)
# define V8_PTR_PREFIX "ll"
# else
# define V8_INTPTR_C(x) (x)
# define V8_PTR_PREFIX ""
# endif // V8_HOST_ARCH_64_BIT
#elif V8_CC_MINGW64
# define V8_UINT64_C(x) (x ## ULL)
# define V8_INT64_C(x) (x ## LL)
# define V8_INTPTR_C(x) (x ## LL)
# define V8_PTR_PREFIX "I64"
#elif V8_HOST_ARCH_64_BIT
# define V8_UINT64_C(x) (x ## ULL)
# define V8_INT64_C(x) (x ## LL)
# else
# define V8_UINT64_C(x) (x ## UL)
# define V8_INT64_C(x) (x ## L)
# endif
# define V8_INTPTR_C(x) (x ## L)
# define V8_PTR_PREFIX "l"
# define V8_UINT64_C(x) (x ## ULL)
# define V8_INT64_C(x) (x ## LL)
# define V8_INTPTR_C(x) (x)
#if V8_OS_AIX
#define V8_PTR_PREFIX "l"
# define V8_PTR_PREFIX ""
#define V8PRIxPTR V8_PTR_PREFIX "x"
#define V8PRIdPTR V8_PTR_PREFIX "d"
#define V8PRIuPTR V8_PTR_PREFIX "u"
// ptrdiff_t is 't' according to the standard, but MSVC uses 'I'.
#if V8_CC_MSVC
#define V8PRIxPTRDIFF "Ix"
#define V8PRIdPTRDIFF "Id"
#define V8PRIuPTRDIFF "Iu"
#define V8PRIxPTRDIFF "tx"
#define V8PRIdPTRDIFF "td"
#define V8PRIuPTRDIFF "tu"
// Fix for Mac OS X defining uintptr_t as "unsigned long":
#undef V8PRIxPTR
#define V8PRIxPTR "lx"
#undef V8PRIdPTR
#define V8PRIdPTR "ld"
#undef V8PRIuPTR
#define V8PRIuPTR "lxu"
// The following macro works on both 32 and 64-bit platforms.
// Usage: instead of writing 0x1234567890123456
// write V8_2PART_UINT64_C(0x12345678,90123456);
#define V8_2PART_UINT64_C(a, b) (((static_cast<uint64_t>(a) << 32) + 0x##b##u))
// Compute the 0-relative offset of some absolute value x of type T.
// This allows conversion of Addresses and integral types into
// 0-relative int offsets.
template <typename T>
inline intptr_t OffsetFrom(T x) {
return x - static_cast<T>(0);
// Compute the absolute value of type T for some 0-relative offset x.
// This allows conversion of 0-relative int offsets into Addresses and
// integral types.
template <typename T>
inline T AddressFrom(intptr_t x) {
return static_cast<T>(static_cast<T>(0) + x);
// Return the largest multiple of m which is <= x.
template <typename T>
inline T RoundDown(T x, intptr_t m) {
return AddressFrom<T>(OffsetFrom(x) & -m);
// Return the smallest multiple of m which is >= x.
template <typename T>
inline T RoundUp(T x, intptr_t m) {
return RoundDown<T>(static_cast<T>(x + m - 1), m);
namespace v8 {
namespace base {
// TODO(yangguo): This is a poor man's replacement for std::is_fundamental,
// which requires C++11. Switch to std::is_fundamental once possible.
template <typename T>
inline bool is_fundamental() {
return false;
template <>
inline bool is_fundamental<uint8_t>() {
return true;
} // namespace base
} // namespace v8
#endif // V8_BASE_MACROS_H_