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Diffstat (limited to 'base/basictypes.h')
| -rw-r--r-- | base/basictypes.h | 367 |
1 files changed, 367 insertions, 0 deletions
diff --git a/base/basictypes.h b/base/basictypes.h new file mode 100644 index 000000000000..c6f509785660 --- /dev/null +++ b/base/basictypes.h @@ -0,0 +1,367 @@ +// Copyright (c) 2011 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 BASE_BASICTYPES_H_ +#define BASE_BASICTYPES_H_ +#pragma once + +#include <limits.h> // So we can set the bounds of our types +#include <stddef.h> // For size_t +#include <string.h> // for memcpy + +#include "base/port.h" // Types that only need exist on certain systems + +#ifndef COMPILER_MSVC +// stdint.h is part of C99 but MSVC doesn't have it. +#include <stdint.h> // For intptr_t. +#endif + +typedef signed char schar; +typedef signed char int8; +typedef short int16; +// TODO: Remove these type guards. These are to avoid conflicts with +// obsolete/protypes.h in the Gecko SDK. +#ifndef _INT32 +#define _INT32 +typedef int int32; +#endif + +// The NSPR system headers define 64-bit as |long| when possible, except on +// Mac OS X. In order to not have typedef mismatches, we do the same on LP64. +// +// On Mac OS X, |long long| is used for 64-bit types for compatibility with +// <inttypes.h> format macros even in the LP64 model. +#if defined(__LP64__) && !defined(OS_MACOSX) +typedef long int64; +#else +typedef long long int64; +#endif + +// NOTE: unsigned types are DANGEROUS in loops and other arithmetical +// places. Use the signed types unless your variable represents a bit +// pattern (eg a hash value) or you really need the extra bit. Do NOT +// use 'unsigned' to express "this value should always be positive"; +// use assertions for this. + +typedef unsigned char uint8; +typedef unsigned short uint16; +// TODO: Remove these type guards. These are to avoid conflicts with +// obsolete/protypes.h in the Gecko SDK. +#ifndef _UINT32 +#define _UINT32 +typedef unsigned int uint32; +#endif + +// See the comment above about NSPR and 64-bit. +#if defined(__LP64__) && !defined(OS_MACOSX) +typedef unsigned long uint64; +#else +typedef unsigned long long uint64; +#endif + +// A type to represent a Unicode code-point value. As of Unicode 4.0, +// such values require up to 21 bits. +// (For type-checking on pointers, make this explicitly signed, +// and it should always be the signed version of whatever int32 is.) +typedef signed int char32; + +const uint8 kuint8max = (( uint8) 0xFF); +const uint16 kuint16max = ((uint16) 0xFFFF); +const uint32 kuint32max = ((uint32) 0xFFFFFFFF); +const uint64 kuint64max = ((uint64) GG_LONGLONG(0xFFFFFFFFFFFFFFFF)); +const int8 kint8min = (( int8) 0x80); +const int8 kint8max = (( int8) 0x7F); +const int16 kint16min = (( int16) 0x8000); +const int16 kint16max = (( int16) 0x7FFF); +const int32 kint32min = (( int32) 0x80000000); +const int32 kint32max = (( int32) 0x7FFFFFFF); +const int64 kint64min = (( int64) GG_LONGLONG(0x8000000000000000)); +const int64 kint64max = (( int64) GG_LONGLONG(0x7FFFFFFFFFFFFFFF)); + +// A macro to disallow the copy constructor and operator= functions +// This should be used in the private: declarations for a class +#define DISALLOW_COPY_AND_ASSIGN(TypeName) \ + TypeName(const TypeName&); \ + void operator=(const TypeName&) + +// An older, deprecated, politically incorrect name for the above. +// NOTE: The usage of this macro was baned from our code base, but some +// third_party libraries are yet using it. +// TODO(tfarina): Figure out how to fix the usage of this macro in the +// third_party libraries and get rid of it. +#define DISALLOW_EVIL_CONSTRUCTORS(TypeName) DISALLOW_COPY_AND_ASSIGN(TypeName) + +// 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]; + +// 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. +#ifndef _MSC_VER +template <typename T, size_t N> +char (&ArraySizeHelper(const T (&array)[N]))[N]; +#endif + +#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))))) + + +// Use implicit_cast as a safe version of static_cast or const_cast +// for upcasting in the type hierarchy (i.e. casting a pointer to Foo +// to a pointer to SuperclassOfFoo or casting a pointer to Foo to +// a const pointer to Foo). +// When you use implicit_cast, the compiler checks that the cast is safe. +// Such explicit implicit_casts are necessary in surprisingly many +// situations where C++ demands an exact type match instead of an +// argument type convertable to a target type. +// +// The From type can be inferred, so the preferred syntax for using +// implicit_cast is the same as for static_cast etc.: +// +// implicit_cast<ToType>(expr) +// +// implicit_cast would have been part of the C++ standard library, +// but the proposal was submitted too late. It will probably make +// its way into the language in the future. +template<typename To, typename From> +inline To implicit_cast(From const &f) { + return f; +} + +// The COMPILE_ASSERT macro can be used to verify that a compile time +// expression is true. For example, you could use it to verify the +// size of a static array: +// +// COMPILE_ASSERT(ARRAYSIZE_UNSAFE(content_type_names) == CONTENT_NUM_TYPES, +// content_type_names_incorrect_size); +// +// or to make sure a struct is smaller than a certain size: +// +// COMPILE_ASSERT(sizeof(foo) < 128, foo_too_large); +// +// The second argument to the macro is the name of the variable. If +// the expression is false, most compilers will issue a warning/error +// containing the name of the variable. + +template <bool> +struct CompileAssert { +}; + +#undef COMPILE_ASSERT +#define COMPILE_ASSERT(expr, msg) \ + typedef CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1] + +// Implementation details of COMPILE_ASSERT: +// +// - COMPILE_ASSERT works by defining an array type that has -1 +// elements (and thus is invalid) when the expression is false. +// +// - The simpler definition +// +// #define COMPILE_ASSERT(expr, msg) typedef char msg[(expr) ? 1 : -1] +// +// does not work, as gcc supports variable-length arrays whose sizes +// are determined at run-time (this is gcc's extension and not part +// of the C++ standard). As a result, gcc fails to reject the +// following code with the simple definition: +// +// int foo; +// COMPILE_ASSERT(foo, msg); // not supposed to compile as foo is +// // not a compile-time constant. +// +// - By using the type CompileAssert<(bool(expr))>, we ensures that +// expr is a compile-time constant. (Template arguments must be +// determined at compile-time.) +// +// - The outer parentheses in CompileAssert<(bool(expr))> are necessary +// to work around a bug in gcc 3.4.4 and 4.0.1. If we had written +// +// CompileAssert<bool(expr)> +// +// instead, these compilers will refuse to compile +// +// COMPILE_ASSERT(5 > 0, some_message); +// +// (They seem to think the ">" in "5 > 0" marks the end of the +// template argument list.) +// +// - The array size is (bool(expr) ? 1 : -1), instead of simply +// +// ((expr) ? 1 : -1). +// +// This is to avoid running into a bug in MS VC 7.1, which +// causes ((0.0) ? 1 : -1) to incorrectly evaluate to 1. + + +// MetatagId refers to metatag-id that we assign to +// each metatag <name, value> pair.. +typedef uint32 MetatagId; + +// Argument type used in interfaces that can optionally take ownership +// of a passed in argument. If TAKE_OWNERSHIP is passed, the called +// object takes ownership of the argument. Otherwise it does not. +enum Ownership { + DO_NOT_TAKE_OWNERSHIP, + TAKE_OWNERSHIP +}; + +// 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 betweeen 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> +inline Dest bit_cast(const Source& source) { + // Compile time assertion: sizeof(Dest) == sizeof(Source) + // A compile error here means your Dest and Source have different sizes. + typedef char VerifySizesAreEqual [sizeof(Dest) == sizeof(Source) ? 1 : -1]; + + Dest dest; + memcpy(&dest, &source, sizeof(dest)); + return dest; +} + +// Used to explicitly mark the return value of a function as unused. If you are +// really sure you don't want to do anything with the return value of a function +// that has been marked WARN_UNUSED_RESULT, wrap it with this. Example: +// +// scoped_ptr<MyType> my_var = ...; +// if (TakeOwnership(my_var.get()) == SUCCESS) +// ignore_result(my_var.release()); +// +template<typename T> +inline void ignore_result(const T& ignored) { +} + +// The following enum should be used only as a constructor argument to indicate +// that the variable has static storage class, and that the constructor should +// do nothing to its state. It indicates to the reader that it is legal to +// declare a static instance of the class, provided the constructor is given +// the base::LINKER_INITIALIZED argument. Normally, it is unsafe to declare a +// static variable that has a constructor or a destructor because invocation +// order is undefined. However, IF the type can be initialized by filling with +// zeroes (which the loader does for static variables), AND the destructor also +// does nothing to the storage, AND there are no virtual methods, then a +// constructor declared as +// explicit MyClass(base::LinkerInitialized x) {} +// and invoked as +// static MyClass my_variable_name(base::LINKER_INITIALIZED); +namespace base { +enum LinkerInitialized { LINKER_INITIALIZED }; +} // base + +#endif // BASE_BASICTYPES_H_ |