// Copyright (c) 2010 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_
#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(mbelshe) Remove these type guards. These are
// temporary to avoid conflicts with npapi.h.
#ifndef _INT32
#define _INT32
typedef int int32;
#endif
// The NSPR system headers define 64-bit as |long| when possible. In order to
// not have typedef mismatches, we do the same on LP64.
#if __LP64__
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(mbelshe) Remove these type guards. These are
// temporary to avoid conflicts with npapi.h.
#ifndef _UINT32
#define _UINT32
typedef unsigned int uint32;
#endif
// See the comment above about NSPR and 64-bit.
#if __LP64__
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.
#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 outter 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;
}
// 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_