basictypes.h revision 3240926e260ce088908e02ac07a6cf7b0c0cbf44
1// Copyright (c) 2011 The Chromium Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style license that can be 3// found in the LICENSE file. 4 5#ifndef BASE_BASICTYPES_H_ 6#define BASE_BASICTYPES_H_ 7 8#include <limits.h> // So we can set the bounds of our types 9#include <stddef.h> // For size_t 10#include <string.h> // for memcpy 11 12#include "base/port.h" // Types that only need exist on certain systems 13 14#ifndef COMPILER_MSVC 15// stdint.h is part of C99 but MSVC doesn't have it. 16#include <stdint.h> // For intptr_t. 17#endif 18 19typedef signed char schar; 20typedef signed char int8; 21typedef short int16; 22typedef int int32; 23 24// The NSPR system headers define 64-bit as |long| when possible, except on 25// Mac OS X. In order to not have typedef mismatches, we do the same on LP64. 26// 27// On Mac OS X, |long long| is used for 64-bit types for compatibility with 28// <inttypes.h> format macros even in the LP64 model. 29#if defined(__LP64__) && !defined(OS_MACOSX) && !defined(OS_OPENBSD) 30typedef long int64; 31#else 32typedef long long int64; 33#endif 34 35// NOTE: It is DANGEROUS to compare signed with unsigned types in loop 36// conditions and other conditional expressions, and it is DANGEROUS to 37// compute object/allocation sizes, indices, and offsets with signed types. 38// Integer overflow behavior for signed types is UNDEFINED in the C/C++ 39// standards, but is defined for unsigned types. 40// 41// Use the unsigned types if your variable represents a bit pattern (e.g. a 42// hash value), object or allocation size, object count, offset, 43// array/vector index, etc. 44// 45// Do NOT use 'unsigned' to express "this value should always be positive"; 46// use assertions for this. 47// 48// See the Chromium style guide for more information. 49// https://sites.google.com/a/chromium.org/dev/developers/coding-style 50 51typedef unsigned char uint8; 52typedef unsigned short uint16; 53typedef unsigned int uint32; 54 55// See the comment above about NSPR and 64-bit. 56#if defined(__LP64__) && !defined(OS_MACOSX) && !defined(OS_OPENBSD) 57typedef unsigned long uint64; 58#else 59typedef unsigned long long uint64; 60#endif 61 62// A type to represent a Unicode code-point value. As of Unicode 4.0, 63// such values require up to 21 bits. 64// (For type-checking on pointers, make this explicitly signed, 65// and it should always be the signed version of whatever int32 is.) 66typedef signed int char32; 67 68const uint8 kuint8max = (( uint8) 0xFF); 69const uint16 kuint16max = ((uint16) 0xFFFF); 70const uint32 kuint32max = ((uint32) 0xFFFFFFFF); 71const uint64 kuint64max = ((uint64) GG_LONGLONG(0xFFFFFFFFFFFFFFFF)); 72const int8 kint8min = (( int8) 0x80); 73const int8 kint8max = (( int8) 0x7F); 74const int16 kint16min = (( int16) 0x8000); 75const int16 kint16max = (( int16) 0x7FFF); 76const int32 kint32min = (( int32) 0x80000000); 77const int32 kint32max = (( int32) 0x7FFFFFFF); 78const int64 kint64min = (( int64) GG_LONGLONG(0x8000000000000000)); 79const int64 kint64max = (( int64) GG_LONGLONG(0x7FFFFFFFFFFFFFFF)); 80 81// Put this in the private: declarations for a class to be uncopyable. 82#define DISALLOW_COPY(TypeName) \ 83 TypeName(const TypeName&) 84 85// Put this in the private: declarations for a class to be unassignable. 86#define DISALLOW_ASSIGN(TypeName) \ 87 void operator=(const TypeName&) 88 89// A macro to disallow the copy constructor and operator= functions 90// This should be used in the private: declarations for a class 91#define DISALLOW_COPY_AND_ASSIGN(TypeName) \ 92 TypeName(const TypeName&); \ 93 void operator=(const TypeName&) 94 95// An older, deprecated, politically incorrect name for the above. 96// NOTE: The usage of this macro was banned from our code base, but some 97// third_party libraries are yet using it. 98// TODO(tfarina): Figure out how to fix the usage of this macro in the 99// third_party libraries and get rid of it. 100#define DISALLOW_EVIL_CONSTRUCTORS(TypeName) DISALLOW_COPY_AND_ASSIGN(TypeName) 101 102// A macro to disallow all the implicit constructors, namely the 103// default constructor, copy constructor and operator= functions. 104// 105// This should be used in the private: declarations for a class 106// that wants to prevent anyone from instantiating it. This is 107// especially useful for classes containing only static methods. 108#define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \ 109 TypeName(); \ 110 DISALLOW_COPY_AND_ASSIGN(TypeName) 111 112// The arraysize(arr) macro returns the # of elements in an array arr. 113// The expression is a compile-time constant, and therefore can be 114// used in defining new arrays, for example. If you use arraysize on 115// a pointer by mistake, you will get a compile-time error. 116// 117// One caveat is that arraysize() doesn't accept any array of an 118// anonymous type or a type defined inside a function. In these rare 119// cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below. This is 120// due to a limitation in C++'s template system. The limitation might 121// eventually be removed, but it hasn't happened yet. 122 123// This template function declaration is used in defining arraysize. 124// Note that the function doesn't need an implementation, as we only 125// use its type. 126template <typename T, size_t N> 127char (&ArraySizeHelper(T (&array)[N]))[N]; 128 129// That gcc wants both of these prototypes seems mysterious. VC, for 130// its part, can't decide which to use (another mystery). Matching of 131// template overloads: the final frontier. 132#ifndef _MSC_VER 133template <typename T, size_t N> 134char (&ArraySizeHelper(const T (&array)[N]))[N]; 135#endif 136 137#define arraysize(array) (sizeof(ArraySizeHelper(array))) 138 139// ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize, 140// but can be used on anonymous types or types defined inside 141// functions. It's less safe than arraysize as it accepts some 142// (although not all) pointers. Therefore, you should use arraysize 143// whenever possible. 144// 145// The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type 146// size_t. 147// 148// ARRAYSIZE_UNSAFE catches a few type errors. If you see a compiler error 149// 150// "warning: division by zero in ..." 151// 152// when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer. 153// You should only use ARRAYSIZE_UNSAFE on statically allocated arrays. 154// 155// The following comments are on the implementation details, and can 156// be ignored by the users. 157// 158// ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in 159// the array) and sizeof(*(arr)) (the # of bytes in one array 160// element). If the former is divisible by the latter, perhaps arr is 161// indeed an array, in which case the division result is the # of 162// elements in the array. Otherwise, arr cannot possibly be an array, 163// and we generate a compiler error to prevent the code from 164// compiling. 165// 166// Since the size of bool is implementation-defined, we need to cast 167// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final 168// result has type size_t. 169// 170// This macro is not perfect as it wrongfully accepts certain 171// pointers, namely where the pointer size is divisible by the pointee 172// size. Since all our code has to go through a 32-bit compiler, 173// where a pointer is 4 bytes, this means all pointers to a type whose 174// size is 3 or greater than 4 will be (righteously) rejected. 175 176#define ARRAYSIZE_UNSAFE(a) \ 177 ((sizeof(a) / sizeof(*(a))) / \ 178 static_cast<size_t>(!(sizeof(a) % sizeof(*(a))))) 179 180 181// Use implicit_cast as a safe version of static_cast or const_cast 182// for upcasting in the type hierarchy (i.e. casting a pointer to Foo 183// to a pointer to SuperclassOfFoo or casting a pointer to Foo to 184// a const pointer to Foo). 185// When you use implicit_cast, the compiler checks that the cast is safe. 186// Such explicit implicit_casts are necessary in surprisingly many 187// situations where C++ demands an exact type match instead of an 188// argument type convertible to a target type. 189// 190// The From type can be inferred, so the preferred syntax for using 191// implicit_cast is the same as for static_cast etc.: 192// 193// implicit_cast<ToType>(expr) 194// 195// implicit_cast would have been part of the C++ standard library, 196// but the proposal was submitted too late. It will probably make 197// its way into the language in the future. 198template<typename To, typename From> 199inline To implicit_cast(From const &f) { 200 return f; 201} 202 203// The COMPILE_ASSERT macro can be used to verify that a compile time 204// expression is true. For example, you could use it to verify the 205// size of a static array: 206// 207// COMPILE_ASSERT(ARRAYSIZE_UNSAFE(content_type_names) == CONTENT_NUM_TYPES, 208// content_type_names_incorrect_size); 209// 210// or to make sure a struct is smaller than a certain size: 211// 212// COMPILE_ASSERT(sizeof(foo) < 128, foo_too_large); 213// 214// The second argument to the macro is the name of the variable. If 215// the expression is false, most compilers will issue a warning/error 216// containing the name of the variable. 217 218template <bool> 219struct CompileAssert { 220}; 221 222#undef COMPILE_ASSERT 223#define COMPILE_ASSERT(expr, msg) \ 224 typedef CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1] 225 226// Implementation details of COMPILE_ASSERT: 227// 228// - COMPILE_ASSERT works by defining an array type that has -1 229// elements (and thus is invalid) when the expression is false. 230// 231// - The simpler definition 232// 233// #define COMPILE_ASSERT(expr, msg) typedef char msg[(expr) ? 1 : -1] 234// 235// does not work, as gcc supports variable-length arrays whose sizes 236// are determined at run-time (this is gcc's extension and not part 237// of the C++ standard). As a result, gcc fails to reject the 238// following code with the simple definition: 239// 240// int foo; 241// COMPILE_ASSERT(foo, msg); // not supposed to compile as foo is 242// // not a compile-time constant. 243// 244// - By using the type CompileAssert<(bool(expr))>, we ensures that 245// expr is a compile-time constant. (Template arguments must be 246// determined at compile-time.) 247// 248// - The outer parentheses in CompileAssert<(bool(expr))> are necessary 249// to work around a bug in gcc 3.4.4 and 4.0.1. If we had written 250// 251// CompileAssert<bool(expr)> 252// 253// instead, these compilers will refuse to compile 254// 255// COMPILE_ASSERT(5 > 0, some_message); 256// 257// (They seem to think the ">" in "5 > 0" marks the end of the 258// template argument list.) 259// 260// - The array size is (bool(expr) ? 1 : -1), instead of simply 261// 262// ((expr) ? 1 : -1). 263// 264// This is to avoid running into a bug in MS VC 7.1, which 265// causes ((0.0) ? 1 : -1) to incorrectly evaluate to 1. 266 267 268// bit_cast<Dest,Source> is a template function that implements the 269// equivalent of "*reinterpret_cast<Dest*>(&source)". We need this in 270// very low-level functions like the protobuf library and fast math 271// support. 272// 273// float f = 3.14159265358979; 274// int i = bit_cast<int32>(f); 275// // i = 0x40490fdb 276// 277// The classical address-casting method is: 278// 279// // WRONG 280// float f = 3.14159265358979; // WRONG 281// int i = * reinterpret_cast<int*>(&f); // WRONG 282// 283// The address-casting method actually produces undefined behavior 284// according to ISO C++ specification section 3.10 -15 -. Roughly, this 285// section says: if an object in memory has one type, and a program 286// accesses it with a different type, then the result is undefined 287// behavior for most values of "different type". 288// 289// This is true for any cast syntax, either *(int*)&f or 290// *reinterpret_cast<int*>(&f). And it is particularly true for 291// conversions between integral lvalues and floating-point lvalues. 292// 293// The purpose of 3.10 -15- is to allow optimizing compilers to assume 294// that expressions with different types refer to different memory. gcc 295// 4.0.1 has an optimizer that takes advantage of this. So a 296// non-conforming program quietly produces wildly incorrect output. 297// 298// The problem is not the use of reinterpret_cast. The problem is type 299// punning: holding an object in memory of one type and reading its bits 300// back using a different type. 301// 302// The C++ standard is more subtle and complex than this, but that 303// is the basic idea. 304// 305// Anyways ... 306// 307// bit_cast<> calls memcpy() which is blessed by the standard, 308// especially by the example in section 3.9 . Also, of course, 309// bit_cast<> wraps up the nasty logic in one place. 310// 311// Fortunately memcpy() is very fast. In optimized mode, with a 312// constant size, gcc 2.95.3, gcc 4.0.1, and msvc 7.1 produce inline 313// code with the minimal amount of data movement. On a 32-bit system, 314// memcpy(d,s,4) compiles to one load and one store, and memcpy(d,s,8) 315// compiles to two loads and two stores. 316// 317// I tested this code with gcc 2.95.3, gcc 4.0.1, icc 8.1, and msvc 7.1. 318// 319// WARNING: if Dest or Source is a non-POD type, the result of the memcpy 320// is likely to surprise you. 321 322template <class Dest, class Source> 323inline Dest bit_cast(const Source& source) { 324 // Compile time assertion: sizeof(Dest) == sizeof(Source) 325 // A compile error here means your Dest and Source have different sizes. 326 typedef char VerifySizesAreEqual [sizeof(Dest) == sizeof(Source) ? 1 : -1]; 327 328 Dest dest; 329 memcpy(&dest, &source, sizeof(dest)); 330 return dest; 331} 332 333// Used to explicitly mark the return value of a function as unused. If you are 334// really sure you don't want to do anything with the return value of a function 335// that has been marked WARN_UNUSED_RESULT, wrap it with this. Example: 336// 337// scoped_ptr<MyType> my_var = ...; 338// if (TakeOwnership(my_var.get()) == SUCCESS) 339// ignore_result(my_var.release()); 340// 341template<typename T> 342inline void ignore_result(const T&) { 343} 344 345// The following enum should be used only as a constructor argument to indicate 346// that the variable has static storage class, and that the constructor should 347// do nothing to its state. It indicates to the reader that it is legal to 348// declare a static instance of the class, provided the constructor is given 349// the base::LINKER_INITIALIZED argument. Normally, it is unsafe to declare a 350// static variable that has a constructor or a destructor because invocation 351// order is undefined. However, IF the type can be initialized by filling with 352// zeroes (which the loader does for static variables), AND the destructor also 353// does nothing to the storage, AND there are no virtual methods, then a 354// constructor declared as 355// explicit MyClass(base::LinkerInitialized x) {} 356// and invoked as 357// static MyClass my_variable_name(base::LINKER_INITIALIZED); 358namespace base { 359enum LinkerInitialized { LINKER_INITIALIZED }; 360 361// Use these to declare and define a static local variable (static T;) so that 362// it is leaked so that its destructors are not called at exit. If you need 363// thread-safe initialization, use base/lazy_instance.h instead. 364#define CR_DEFINE_STATIC_LOCAL(type, name, arguments) \ 365 static type& name = *new type arguments 366 367} // base 368 369#endif // BASE_BASICTYPES_H_ 370