1// Copyright (c) 2010 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; 22// TODO(mbelshe) Remove these type guards. These are 23// temporary to avoid conflicts with npapi.h. 24#ifndef _INT32 25#define _INT32 26typedef int int32; 27#endif 28 29// The NSPR system headers define 64-bit as |long| when possible. In order to 30// not have typedef mismatches, we do the same on LP64. 31#if __LP64__ 32typedef long int64; 33#else 34typedef long long int64; 35#endif 36 37// NOTE: unsigned types are DANGEROUS in loops and other arithmetical 38// places. Use the signed types unless your variable represents a bit 39// pattern (eg a hash value) or you really need the extra bit. Do NOT 40// use 'unsigned' to express "this value should always be positive"; 41// use assertions for this. 42 43typedef unsigned char uint8; 44typedef unsigned short uint16; 45// TODO(mbelshe) Remove these type guards. These are 46// temporary to avoid conflicts with npapi.h. 47#ifndef _UINT32 48#define _UINT32 49typedef unsigned int uint32; 50#endif 51 52// See the comment above about NSPR and 64-bit. 53#if __LP64__ 54typedef unsigned long uint64; 55#else 56typedef unsigned long long uint64; 57#endif 58 59// A type to represent a Unicode code-point value. As of Unicode 4.0, 60// such values require up to 21 bits. 61// (For type-checking on pointers, make this explicitly signed, 62// and it should always be the signed version of whatever int32 is.) 63typedef signed int char32; 64 65const uint8 kuint8max = (( uint8) 0xFF); 66const uint16 kuint16max = ((uint16) 0xFFFF); 67const uint32 kuint32max = ((uint32) 0xFFFFFFFF); 68const uint64 kuint64max = ((uint64) GG_LONGLONG(0xFFFFFFFFFFFFFFFF)); 69const int8 kint8min = (( int8) 0x80); 70const int8 kint8max = (( int8) 0x7F); 71const int16 kint16min = (( int16) 0x8000); 72const int16 kint16max = (( int16) 0x7FFF); 73const int32 kint32min = (( int32) 0x80000000); 74const int32 kint32max = (( int32) 0x7FFFFFFF); 75const int64 kint64min = (( int64) GG_LONGLONG(0x8000000000000000)); 76const int64 kint64max = (( int64) GG_LONGLONG(0x7FFFFFFFFFFFFFFF)); 77 78// A macro to disallow the copy constructor and operator= functions 79// This should be used in the private: declarations for a class 80#define DISALLOW_COPY_AND_ASSIGN(TypeName) \ 81 TypeName(const TypeName&); \ 82 void operator=(const TypeName&) 83 84// An older, deprecated, politically incorrect name for the above. 85#define DISALLOW_EVIL_CONSTRUCTORS(TypeName) DISALLOW_COPY_AND_ASSIGN(TypeName) 86 87// A macro to disallow all the implicit constructors, namely the 88// default constructor, copy constructor and operator= functions. 89// 90// This should be used in the private: declarations for a class 91// that wants to prevent anyone from instantiating it. This is 92// especially useful for classes containing only static methods. 93#define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \ 94 TypeName(); \ 95 DISALLOW_COPY_AND_ASSIGN(TypeName) 96 97// The arraysize(arr) macro returns the # of elements in an array arr. 98// The expression is a compile-time constant, and therefore can be 99// used in defining new arrays, for example. If you use arraysize on 100// a pointer by mistake, you will get a compile-time error. 101// 102// One caveat is that arraysize() doesn't accept any array of an 103// anonymous type or a type defined inside a function. In these rare 104// cases, you have to use the unsafe ARRAYSIZE_UNSAFE() macro below. This is 105// due to a limitation in C++'s template system. The limitation might 106// eventually be removed, but it hasn't happened yet. 107 108// This template function declaration is used in defining arraysize. 109// Note that the function doesn't need an implementation, as we only 110// use its type. 111template <typename T, size_t N> 112char (&ArraySizeHelper(T (&array)[N]))[N]; 113 114// That gcc wants both of these prototypes seems mysterious. VC, for 115// its part, can't decide which to use (another mystery). Matching of 116// template overloads: the final frontier. 117#ifndef _MSC_VER 118template <typename T, size_t N> 119char (&ArraySizeHelper(const T (&array)[N]))[N]; 120#endif 121 122#define arraysize(array) (sizeof(ArraySizeHelper(array))) 123 124// ARRAYSIZE_UNSAFE performs essentially the same calculation as arraysize, 125// but can be used on anonymous types or types defined inside 126// functions. It's less safe than arraysize as it accepts some 127// (although not all) pointers. Therefore, you should use arraysize 128// whenever possible. 129// 130// The expression ARRAYSIZE_UNSAFE(a) is a compile-time constant of type 131// size_t. 132// 133// ARRAYSIZE_UNSAFE catches a few type errors. If you see a compiler error 134// 135// "warning: division by zero in ..." 136// 137// when using ARRAYSIZE_UNSAFE, you are (wrongfully) giving it a pointer. 138// You should only use ARRAYSIZE_UNSAFE on statically allocated arrays. 139// 140// The following comments are on the implementation details, and can 141// be ignored by the users. 142// 143// ARRAYSIZE_UNSAFE(arr) works by inspecting sizeof(arr) (the # of bytes in 144// the array) and sizeof(*(arr)) (the # of bytes in one array 145// element). If the former is divisible by the latter, perhaps arr is 146// indeed an array, in which case the division result is the # of 147// elements in the array. Otherwise, arr cannot possibly be an array, 148// and we generate a compiler error to prevent the code from 149// compiling. 150// 151// Since the size of bool is implementation-defined, we need to cast 152// !(sizeof(a) & sizeof(*(a))) to size_t in order to ensure the final 153// result has type size_t. 154// 155// This macro is not perfect as it wrongfully accepts certain 156// pointers, namely where the pointer size is divisible by the pointee 157// size. Since all our code has to go through a 32-bit compiler, 158// where a pointer is 4 bytes, this means all pointers to a type whose 159// size is 3 or greater than 4 will be (righteously) rejected. 160 161#define ARRAYSIZE_UNSAFE(a) \ 162 ((sizeof(a) / sizeof(*(a))) / \ 163 static_cast<size_t>(!(sizeof(a) % sizeof(*(a))))) 164 165 166// Use implicit_cast as a safe version of static_cast or const_cast 167// for upcasting in the type hierarchy (i.e. casting a pointer to Foo 168// to a pointer to SuperclassOfFoo or casting a pointer to Foo to 169// a const pointer to Foo). 170// When you use implicit_cast, the compiler checks that the cast is safe. 171// Such explicit implicit_casts are necessary in surprisingly many 172// situations where C++ demands an exact type match instead of an 173// argument type convertable to a target type. 174// 175// The From type can be inferred, so the preferred syntax for using 176// implicit_cast is the same as for static_cast etc.: 177// 178// implicit_cast<ToType>(expr) 179// 180// implicit_cast would have been part of the C++ standard library, 181// but the proposal was submitted too late. It will probably make 182// its way into the language in the future. 183template<typename To, typename From> 184inline To implicit_cast(From const &f) { 185 return f; 186} 187 188// The COMPILE_ASSERT macro can be used to verify that a compile time 189// expression is true. For example, you could use it to verify the 190// size of a static array: 191// 192// COMPILE_ASSERT(ARRAYSIZE_UNSAFE(content_type_names) == CONTENT_NUM_TYPES, 193// content_type_names_incorrect_size); 194// 195// or to make sure a struct is smaller than a certain size: 196// 197// COMPILE_ASSERT(sizeof(foo) < 128, foo_too_large); 198// 199// The second argument to the macro is the name of the variable. If 200// the expression is false, most compilers will issue a warning/error 201// containing the name of the variable. 202 203template <bool> 204struct CompileAssert { 205}; 206 207#undef COMPILE_ASSERT 208#define COMPILE_ASSERT(expr, msg) \ 209 typedef CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1] 210 211// Implementation details of COMPILE_ASSERT: 212// 213// - COMPILE_ASSERT works by defining an array type that has -1 214// elements (and thus is invalid) when the expression is false. 215// 216// - The simpler definition 217// 218// #define COMPILE_ASSERT(expr, msg) typedef char msg[(expr) ? 1 : -1] 219// 220// does not work, as gcc supports variable-length arrays whose sizes 221// are determined at run-time (this is gcc's extension and not part 222// of the C++ standard). As a result, gcc fails to reject the 223// following code with the simple definition: 224// 225// int foo; 226// COMPILE_ASSERT(foo, msg); // not supposed to compile as foo is 227// // not a compile-time constant. 228// 229// - By using the type CompileAssert<(bool(expr))>, we ensures that 230// expr is a compile-time constant. (Template arguments must be 231// determined at compile-time.) 232// 233// - The outter parentheses in CompileAssert<(bool(expr))> are necessary 234// to work around a bug in gcc 3.4.4 and 4.0.1. If we had written 235// 236// CompileAssert<bool(expr)> 237// 238// instead, these compilers will refuse to compile 239// 240// COMPILE_ASSERT(5 > 0, some_message); 241// 242// (They seem to think the ">" in "5 > 0" marks the end of the 243// template argument list.) 244// 245// - The array size is (bool(expr) ? 1 : -1), instead of simply 246// 247// ((expr) ? 1 : -1). 248// 249// This is to avoid running into a bug in MS VC 7.1, which 250// causes ((0.0) ? 1 : -1) to incorrectly evaluate to 1. 251 252 253// MetatagId refers to metatag-id that we assign to 254// each metatag <name, value> pair.. 255typedef uint32 MetatagId; 256 257// Argument type used in interfaces that can optionally take ownership 258// of a passed in argument. If TAKE_OWNERSHIP is passed, the called 259// object takes ownership of the argument. Otherwise it does not. 260enum Ownership { 261 DO_NOT_TAKE_OWNERSHIP, 262 TAKE_OWNERSHIP 263}; 264 265// bit_cast<Dest,Source> is a template function that implements the 266// equivalent of "*reinterpret_cast<Dest*>(&source)". We need this in 267// very low-level functions like the protobuf library and fast math 268// support. 269// 270// float f = 3.14159265358979; 271// int i = bit_cast<int32>(f); 272// // i = 0x40490fdb 273// 274// The classical address-casting method is: 275// 276// // WRONG 277// float f = 3.14159265358979; // WRONG 278// int i = * reinterpret_cast<int*>(&f); // WRONG 279// 280// The address-casting method actually produces undefined behavior 281// according to ISO C++ specification section 3.10 -15 -. Roughly, this 282// section says: if an object in memory has one type, and a program 283// accesses it with a different type, then the result is undefined 284// behavior for most values of "different type". 285// 286// This is true for any cast syntax, either *(int*)&f or 287// *reinterpret_cast<int*>(&f). And it is particularly true for 288// conversions betweeen integral lvalues and floating-point lvalues. 289// 290// The purpose of 3.10 -15- is to allow optimizing compilers to assume 291// that expressions with different types refer to different memory. gcc 292// 4.0.1 has an optimizer that takes advantage of this. So a 293// non-conforming program quietly produces wildly incorrect output. 294// 295// The problem is not the use of reinterpret_cast. The problem is type 296// punning: holding an object in memory of one type and reading its bits 297// back using a different type. 298// 299// The C++ standard is more subtle and complex than this, but that 300// is the basic idea. 301// 302// Anyways ... 303// 304// bit_cast<> calls memcpy() which is blessed by the standard, 305// especially by the example in section 3.9 . Also, of course, 306// bit_cast<> wraps up the nasty logic in one place. 307// 308// Fortunately memcpy() is very fast. In optimized mode, with a 309// constant size, gcc 2.95.3, gcc 4.0.1, and msvc 7.1 produce inline 310// code with the minimal amount of data movement. On a 32-bit system, 311// memcpy(d,s,4) compiles to one load and one store, and memcpy(d,s,8) 312// compiles to two loads and two stores. 313// 314// I tested this code with gcc 2.95.3, gcc 4.0.1, icc 8.1, and msvc 7.1. 315// 316// WARNING: if Dest or Source is a non-POD type, the result of the memcpy 317// is likely to surprise you. 318 319template <class Dest, class Source> 320inline Dest bit_cast(const Source& source) { 321 // Compile time assertion: sizeof(Dest) == sizeof(Source) 322 // A compile error here means your Dest and Source have different sizes. 323 typedef char VerifySizesAreEqual [sizeof(Dest) == sizeof(Source) ? 1 : -1]; 324 325 Dest dest; 326 memcpy(&dest, &source, sizeof(dest)); 327 return dest; 328} 329 330// The following enum should be used only as a constructor argument to indicate 331// that the variable has static storage class, and that the constructor should 332// do nothing to its state. It indicates to the reader that it is legal to 333// declare a static instance of the class, provided the constructor is given 334// the base::LINKER_INITIALIZED argument. Normally, it is unsafe to declare a 335// static variable that has a constructor or a destructor because invocation 336// order is undefined. However, IF the type can be initialized by filling with 337// zeroes (which the loader does for static variables), AND the destructor also 338// does nothing to the storage, AND there are no virtual methods, then a 339// constructor declared as 340// explicit MyClass(base::LinkerInitialized x) {} 341// and invoked as 342// static MyClass my_variable_name(base::LINKER_INITIALIZED); 343namespace base { 344enum LinkerInitialized { LINKER_INITIALIZED }; 345} // base 346 347// UnaligndLoad32 is put here instead of base/port.h to 348// avoid the circular dependency between port.h and basictypes.h 349// ARM does not support unaligned memory access. 350#if defined(ARCH_CPU_X86_FAMILY) 351// x86 and x86-64 can perform unaligned loads/stores directly; 352inline uint32 UnalignedLoad32(const void* p) { 353 return *reinterpret_cast<const uint32*>(p); 354} 355#else 356#define NEED_ALIGNED_LOADS 357// If target architecture does not support unaligned loads and stores, 358// use memcpy version of UNALIGNED_LOAD32. 359inline uint32 UnalignedLoad32(const void* p) { 360 uint32 t; 361 memcpy(&t, reinterpret_cast<const uint8*>(p), sizeof(t)); 362 return t; 363} 364 365#endif 366#endif // BASE_BASICTYPES_H_ 367