446 lines
17 KiB
C++
446 lines
17 KiB
C++
// Copyright 2014 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// This file contains macros and macro-like constructs (e.g., templates) that
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// are commonly used throughout Chromium source. (It may also contain things
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// that are closely related to things that are commonly used that belong in this
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// file.)
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#ifndef BUTIL_MACROS_H_
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#define BUTIL_MACROS_H_
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#include <stddef.h> // For size_t.
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#include <string.h> // For memcpy.
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#include "butil/compiler_specific.h" // For ALLOW_UNUSED.
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// There must be many copy-paste versions of these macros which are same
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// things, undefine them to avoid conflict.
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#undef DISALLOW_COPY
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#undef DISALLOW_ASSIGN
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#undef DISALLOW_COPY_AND_ASSIGN
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#undef DISALLOW_EVIL_CONSTRUCTORS
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#undef DISALLOW_IMPLICIT_CONSTRUCTORS
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#if !defined(BUTIL_CXX11_ENABLED)
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#define BUTIL_DELETE_FUNCTION(decl) decl
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#else
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#define BUTIL_DELETE_FUNCTION(decl) decl = delete
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#endif
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// Put this in the private: declarations for a class to be uncopyable.
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#define DISALLOW_COPY(TypeName) \
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BUTIL_DELETE_FUNCTION(TypeName(const TypeName&))
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// Put this in the private: declarations for a class to be unassignable.
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#define DISALLOW_ASSIGN(TypeName) \
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BUTIL_DELETE_FUNCTION(void operator=(const TypeName&))
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// A macro to disallow the copy constructor and operator= functions
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// This should be used in the private: declarations for a class
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#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
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BUTIL_DELETE_FUNCTION(TypeName(const TypeName&)); \
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BUTIL_DELETE_FUNCTION(void operator=(const TypeName&))
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// An older, deprecated, politically incorrect name for the above.
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// NOTE: The usage of this macro was banned from our code base, but some
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// third_party libraries are yet using it.
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// TODO(tfarina): Figure out how to fix the usage of this macro in the
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// third_party libraries and get rid of it.
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#define DISALLOW_EVIL_CONSTRUCTORS(TypeName) DISALLOW_COPY_AND_ASSIGN(TypeName)
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// A macro to disallow all the implicit constructors, namely the
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// default constructor, copy constructor and operator= functions.
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//
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// This should be used in the private: declarations for a class
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// that wants to prevent anyone from instantiating it. This is
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// especially useful for classes containing only static methods.
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#define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
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BUTIL_DELETE_FUNCTION(TypeName()); \
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DISALLOW_COPY_AND_ASSIGN(TypeName)
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// Concatenate numbers in c/c++ macros.
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#ifndef BAIDU_CONCAT
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# define BAIDU_CONCAT(a, b) BAIDU_CONCAT_HELPER(a, b)
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# define BAIDU_CONCAT_HELPER(a, b) a##b
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#endif
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#undef arraysize
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// The arraysize(arr) macro returns the # of elements in an array arr.
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// The expression is a compile-time constant, and therefore can be
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// used in defining new arrays, for example. If you use arraysize on
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// a pointer by mistake, you will get a compile-time error.
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//
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// One caveat is that arraysize() doesn't accept any array of an
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// anonymous type or a type defined inside a function. In these rare
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// cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below. This is
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// due to a limitation in C++'s template system. The limitation might
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// eventually be removed, but it hasn't happened yet.
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// This template function declaration is used in defining arraysize.
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// Note that the function doesn't need an implementation, as we only
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// use its type.
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namespace butil {
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template <typename T, size_t N>
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char (&ArraySizeHelper(T (&array)[N]))[N];
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}
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// That gcc wants both of these prototypes seems mysterious. VC, for
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// its part, can't decide which to use (another mystery). Matching of
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// template overloads: the final frontier.
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#ifndef _MSC_VER
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namespace butil {
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template <typename T, size_t N>
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char (&ArraySizeHelper(const T (&array)[N]))[N];
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}
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#endif
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#define arraysize(array) (sizeof(::butil::ArraySizeHelper(array)))
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// gejun: Following macro was used in other modules.
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#undef ARRAY_SIZE
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#define ARRAY_SIZE(array) arraysize(array)
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// ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize,
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// but can be used on anonymous types or types defined inside
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// functions. It's less safe than arraysize as it accepts some
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// (although not all) pointers. Therefore, you should use arraysize
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// whenever possible.
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//
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// The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type
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// size_t.
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//
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// ARRAYSIZE_UNSAFE catches a few type errors. If you see a compiler error
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//
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// "warning: division by zero in ..."
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//
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// when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer.
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// You should only use ARRAYSIZE_UNSAFE on statically allocated arrays.
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//
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// The following comments are on the implementation details, and can
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// be ignored by the users.
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//
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// ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in
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// the array) and sizeof(*(arr)) (the # of bytes in one array
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// element). If the former is divisible by the latter, perhaps arr is
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// indeed an array, in which case the division result is the # of
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// elements in the array. Otherwise, arr cannot possibly be an array,
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// and we generate a compiler error to prevent the code from
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// compiling.
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//
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// Since the size of bool is implementation-defined, we need to cast
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// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final
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// result has type size_t.
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//
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// This macro is not perfect as it wrongfully accepts certain
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// pointers, namely where the pointer size is divisible by the pointee
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// size. Since all our code has to go through a 32-bit compiler,
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// where a pointer is 4 bytes, this means all pointers to a type whose
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// size is 3 or greater than 4 will be (righteously) rejected.
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#undef ARRAYSIZE_UNSAFE
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#define ARRAYSIZE_UNSAFE(a) \
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((sizeof(a) / sizeof(*(a))) / \
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static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))
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// Use implicit_cast as a safe version of static_cast or const_cast
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// for upcasting in the type hierarchy (i.e. casting a pointer to Foo
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// to a pointer to SuperclassOfFoo or casting a pointer to Foo to
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// a const pointer to Foo).
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// When you use implicit_cast, the compiler checks that the cast is safe.
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// Such explicit implicit_casts are necessary in surprisingly many
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// situations where C++ demands an exact type match instead of an
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// argument type convertible to a target type.
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//
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// The From type can be inferred, so the preferred syntax for using
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// implicit_cast is the same as for static_cast etc.:
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//
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// implicit_cast<ToType>(expr)
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//
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// implicit_cast would have been part of the C++ standard library,
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// but the proposal was submitted too late. It will probably make
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// its way into the language in the future.
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namespace butil {
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template<typename To, typename From>
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inline To implicit_cast(From const &f) {
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return f;
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}
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}
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#if defined(BUTIL_CXX11_ENABLED)
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// C++11 supports compile-time assertion directly
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#define BAIDU_CASSERT(expr, msg) static_assert(expr, #msg)
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#else
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// Assert constant boolean expressions at compile-time
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// Params:
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// expr the constant expression to be checked
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// msg an error infomation conforming name conventions of C/C++
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// variables(alphabets/numbers/underscores, no blanks). For
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// example "cannot_accept_a_number_bigger_than_128" is valid
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// while "this number is out-of-range" is illegal.
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//
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// when an asssertion like "BAIDU_CASSERT(false, you_should_not_be_here)"
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// breaks, a compilation error is printed:
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//
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// foo.cpp:401: error: enumerator value for `you_should_not_be_here___19' not
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// integer constant
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//
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// You can call BAIDU_CASSERT at global scope, inside a class or a function
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//
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// BAIDU_CASSERT(false, you_should_not_be_here);
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// int main () { ... }
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//
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// struct Foo {
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// BAIDU_CASSERT(1 == 0, Never_equals);
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// };
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//
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// int bar(...)
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// {
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// BAIDU_CASSERT (value < 10, invalid_value);
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// }
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//
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namespace butil {
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template <bool> struct CAssert { static const int x = 1; };
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template <> struct CAssert<false> { static const char * x; };
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}
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#define BAIDU_CASSERT(expr, msg) \
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enum { BAIDU_CONCAT(BAIDU_CONCAT(LINE_, __LINE__), __##msg) \
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= ::butil::CAssert<!!(expr)>::x };
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#endif // BUTIL_CXX11_ENABLED
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// The impl. of chrome does not work for offsetof(Object, private_filed)
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#undef COMPILE_ASSERT
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#define COMPILE_ASSERT(expr, msg) BAIDU_CASSERT(expr, msg)
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// bit_cast<Dest,Source> is a template function that implements the
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// equivalent of "*reinterpret_cast<Dest*>(&source)". We need this in
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// very low-level functions like the protobuf library and fast math
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// support.
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//
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// float f = 3.14159265358979;
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// int i = bit_cast<int32_t>(f);
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// // i = 0x40490fdb
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//
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// The classical address-casting method is:
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//
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// // WRONG
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// float f = 3.14159265358979; // WRONG
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// int i = * reinterpret_cast<int*>(&f); // WRONG
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//
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// The address-casting method actually produces undefined behavior
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// according to ISO C++ specification section 3.10 -15 -. Roughly, this
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// section says: if an object in memory has one type, and a program
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// accesses it with a different type, then the result is undefined
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// behavior for most values of "different type".
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//
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// This is true for any cast syntax, either *(int*)&f or
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// *reinterpret_cast<int*>(&f). And it is particularly true for
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// conversions between integral lvalues and floating-point lvalues.
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//
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// The purpose of 3.10 -15- is to allow optimizing compilers to assume
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// that expressions with different types refer to different memory. gcc
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// 4.0.1 has an optimizer that takes advantage of this. So a
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// non-conforming program quietly produces wildly incorrect output.
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//
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// The problem is not the use of reinterpret_cast. The problem is type
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// punning: holding an object in memory of one type and reading its bits
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// back using a different type.
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//
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// The C++ standard is more subtle and complex than this, but that
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// is the basic idea.
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//
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// Anyways ...
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//
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// bit_cast<> calls memcpy() which is blessed by the standard,
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// especially by the example in section 3.9 . Also, of course,
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// bit_cast<> wraps up the nasty logic in one place.
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//
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// Fortunately memcpy() is very fast. In optimized mode, with a
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// constant size, gcc 2.95.3, gcc 4.0.1, and msvc 7.1 produce inline
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// code with the minimal amount of data movement. On a 32-bit system,
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// memcpy(d,s,4) compiles to one load and one store, and memcpy(d,s,8)
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// compiles to two loads and two stores.
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//
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// I tested this code with gcc 2.95.3, gcc 4.0.1, icc 8.1, and msvc 7.1.
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//
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// WARNING: if Dest or Source is a non-POD type, the result of the memcpy
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// is likely to surprise you.
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namespace butil {
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template <class Dest, class Source>
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inline Dest bit_cast(const Source& source) {
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COMPILE_ASSERT(sizeof(Dest) == sizeof(Source), VerifySizesAreEqual);
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Dest dest;
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memcpy(&dest, &source, sizeof(dest));
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return dest;
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}
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} // namespace butil
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// Used to explicitly mark the return value of a function as unused. If you are
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// really sure you don't want to do anything with the return value of a function
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// that has been marked WARN_UNUSED_RESULT, wrap it with this. Example:
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//
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// scoped_ptr<MyType> my_var = ...;
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// if (TakeOwnership(my_var.get()) == SUCCESS)
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// ignore_result(my_var.release());
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//
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namespace butil {
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template<typename T>
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inline void ignore_result(const T&) {
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}
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} // namespace butil
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// The following enum should be used only as a constructor argument to indicate
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// that the variable has static storage class, and that the constructor should
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// do nothing to its state. It indicates to the reader that it is legal to
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// declare a static instance of the class, provided the constructor is given
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// the butil::LINKER_INITIALIZED argument. Normally, it is unsafe to declare a
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// static variable that has a constructor or a destructor because invocation
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// order is undefined. However, IF the type can be initialized by filling with
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// zeroes (which the loader does for static variables), AND the destructor also
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// does nothing to the storage, AND there are no virtual methods, then a
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// constructor declared as
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// explicit MyClass(butil::LinkerInitialized x) {}
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// and invoked as
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// static MyClass my_variable_name(butil::LINKER_INITIALIZED);
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namespace butil {
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enum LinkerInitialized { LINKER_INITIALIZED };
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// Use these to declare and define a static local variable (static T;) so that
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// it is leaked so that its destructors are not called at exit. If you need
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// thread-safe initialization, use butil/lazy_instance.h instead.
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#undef CR_DEFINE_STATIC_LOCAL
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#define CR_DEFINE_STATIC_LOCAL(type, name, arguments) \
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static type& name = *new type arguments
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} // namespace butil
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// Convert symbol to string
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#ifndef BAIDU_SYMBOLSTR
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# define BAIDU_SYMBOLSTR(a) BAIDU_SYMBOLSTR_HELPER(a)
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# define BAIDU_SYMBOLSTR_HELPER(a) #a
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#endif
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#ifndef BAIDU_TYPEOF
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# if defined(BUTIL_CXX11_ENABLED)
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# define BAIDU_TYPEOF decltype
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# else
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# ifdef _MSC_VER
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# include <boost/typeof/typeof.hpp>
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# define BAIDU_TYPEOF BOOST_TYPEOF
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# else
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# define BAIDU_TYPEOF typeof
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# endif
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# endif // BUTIL_CXX11_ENABLED
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#endif // BAIDU_TYPEOF
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// ptr: the pointer to the member.
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// type: the type of the container struct this is embedded in.
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// member: the name of the member within the struct.
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#ifndef container_of
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# define container_of(ptr, type, member) ({ \
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const BAIDU_TYPEOF( ((type *)0)->member ) *__mptr = (ptr); \
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(type *)( (char *)__mptr - offsetof(type,member) );})
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#endif
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// DEFINE_SMALL_ARRAY(MyType, my_array, size, 64);
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// my_array is typed `MyType*' and as long as `size'. If `size' is not
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// greater than 64, the array is allocated on stack.
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//
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// NOTE: NEVER use ARRAY_SIZE(my_array) which is always 1.
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#if defined(__cplusplus)
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namespace butil {
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namespace internal {
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template <typename T> struct ArrayDeleter {
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ArrayDeleter() : arr(0) {}
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~ArrayDeleter() { delete[] arr; }
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T* arr;
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};
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}}
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// Many versions of clang does not support variable-length array with non-pod
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// types, have to implement the macro differently.
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#if !defined(__clang__)
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# define DEFINE_SMALL_ARRAY(Tp, name, size, maxsize) \
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Tp* name = 0; \
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const unsigned name##_size = (size); \
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const unsigned name##_stack_array_size = (name##_size <= (maxsize) ? name##_size : 0); \
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Tp name##_stack_array[name##_stack_array_size]; \
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::butil::internal::ArrayDeleter<Tp> name##_array_deleter; \
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if (name##_stack_array_size) { \
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name = name##_stack_array; \
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} else { \
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name = new (::std::nothrow) Tp[name##_size]; \
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name##_array_deleter.arr = name; \
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}
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#else
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// This implementation works for GCC as well, however it needs extra 16 bytes
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// for ArrayCtorDtor.
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namespace butil {
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namespace internal {
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template <typename T> struct ArrayCtorDtor {
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ArrayCtorDtor(void* arr, unsigned size) : _arr((T*)arr), _size(size) {
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for (unsigned i = 0; i < size; ++i) { new (_arr + i) T; }
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}
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~ArrayCtorDtor() {
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for (unsigned i = 0; i < _size; ++i) { _arr[i].~T(); }
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}
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private:
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T* _arr;
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unsigned _size;
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};
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}}
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# define DEFINE_SMALL_ARRAY(Tp, name, size, maxsize) \
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Tp* name = 0; \
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const unsigned name##_size = (size); \
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const unsigned name##_stack_array_size = (name##_size <= (maxsize) ? name##_size : 0); \
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char name##_stack_array[sizeof(Tp) * name##_stack_array_size]; \
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::butil::internal::ArrayDeleter<char> name##_array_deleter; \
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if (name##_stack_array_size) { \
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name = (Tp*)name##_stack_array; \
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} else { \
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name = (Tp*)new (::std::nothrow) char[sizeof(Tp) * name##_size];\
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name##_array_deleter.arr = (char*)name; \
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} \
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const ::butil::internal::ArrayCtorDtor<Tp> name##_array_ctor_dtor(name, name##_size);
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#endif // !defined(__clang__)
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#endif // defined(__cplusplus)
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// Put following code somewhere global to run it before main():
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//
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// BAIDU_GLOBAL_INIT()
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// {
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// ... your code ...
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// }
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//
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// Your can:
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// * Write any code and access global variables.
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// * Use ASSERT_*.
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// * Have multiple BAIDU_GLOBAL_INIT() in one scope.
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//
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// Since the code run in global scope, quit with exit() or similar functions.
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#if defined(__cplusplus)
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# define BAIDU_GLOBAL_INIT \
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namespace { /*anonymous namespace */ \
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struct BAIDU_CONCAT(BaiduGlobalInit, __LINE__) { \
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BAIDU_CONCAT(BaiduGlobalInit, __LINE__)() { init(); } \
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void init(); \
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} BAIDU_CONCAT(baidu_global_init_dummy_, __LINE__); \
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} /* anonymous namespace */ \
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void BAIDU_CONCAT(BaiduGlobalInit, __LINE__)::init
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#else
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# define BAIDU_GLOBAL_INIT \
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static void __attribute__((constructor)) \
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BAIDU_CONCAT(baidu_global_init_, __LINE__)
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#endif // __cplusplus
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#endif // BUTIL_MACROS_H_
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