зеркало из https://github.com/mozilla/gecko-dev.git
336 строки
9.0 KiB
C++
336 строки
9.0 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
|
|
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
/*
|
|
* Miscellaneous uncategorized functionality. Please add new functionality to
|
|
* new headers, or to other appropriate existing headers, not here.
|
|
*/
|
|
|
|
#ifndef mozilla_Util_h_
|
|
#define mozilla_Util_h_
|
|
|
|
#include "mozilla/Assertions.h"
|
|
#include "mozilla/Attributes.h"
|
|
#include "mozilla/Types.h"
|
|
|
|
#ifdef __cplusplus
|
|
|
|
namespace mozilla {
|
|
|
|
/*
|
|
* This class, and the corresponding macro MOZ_ALIGNOF, figure out how many
|
|
* bytes of alignment a given type needs.
|
|
*/
|
|
template<class T>
|
|
class AlignmentFinder
|
|
{
|
|
struct Aligner
|
|
{
|
|
char c;
|
|
T t;
|
|
};
|
|
|
|
public:
|
|
static const size_t alignment = sizeof(Aligner) - sizeof(T);
|
|
};
|
|
|
|
#define MOZ_ALIGNOF(T) mozilla::AlignmentFinder<T>::alignment
|
|
|
|
/*
|
|
* Declare the MOZ_ALIGNED_DECL macro for declaring aligned types.
|
|
*
|
|
* For instance,
|
|
*
|
|
* MOZ_ALIGNED_DECL(char arr[2], 8);
|
|
*
|
|
* will declare a two-character array |arr| aligned to 8 bytes.
|
|
*/
|
|
|
|
#if defined(__GNUC__)
|
|
# define MOZ_ALIGNED_DECL(_type, _align) \
|
|
_type __attribute__((aligned(_align)))
|
|
#elif defined(_MSC_VER)
|
|
# define MOZ_ALIGNED_DECL(_type, _align) \
|
|
__declspec(align(_align)) _type
|
|
#else
|
|
# warning "We don't know how to align variables on this compiler."
|
|
# define MOZ_ALIGNED_DECL(_type, _align) _type
|
|
#endif
|
|
|
|
/*
|
|
* AlignedElem<N> is a structure whose alignment is guaranteed to be at least N
|
|
* bytes.
|
|
*
|
|
* We support 1, 2, 4, 8, and 16-bit alignment.
|
|
*/
|
|
template<size_t align>
|
|
struct AlignedElem;
|
|
|
|
/*
|
|
* We have to specialize this template because GCC doesn't like __attribute__((aligned(foo))) where
|
|
* foo is a template parameter.
|
|
*/
|
|
|
|
template<>
|
|
struct AlignedElem<1>
|
|
{
|
|
MOZ_ALIGNED_DECL(uint8_t elem, 1);
|
|
};
|
|
|
|
template<>
|
|
struct AlignedElem<2>
|
|
{
|
|
MOZ_ALIGNED_DECL(uint8_t elem, 2);
|
|
};
|
|
|
|
template<>
|
|
struct AlignedElem<4>
|
|
{
|
|
MOZ_ALIGNED_DECL(uint8_t elem, 4);
|
|
};
|
|
|
|
template<>
|
|
struct AlignedElem<8>
|
|
{
|
|
MOZ_ALIGNED_DECL(uint8_t elem, 8);
|
|
};
|
|
|
|
template<>
|
|
struct AlignedElem<16>
|
|
{
|
|
MOZ_ALIGNED_DECL(uint8_t elem, 16);
|
|
};
|
|
|
|
/*
|
|
* This utility pales in comparison to Boost's aligned_storage. The utility
|
|
* simply assumes that uint64_t is enough alignment for anyone. This may need
|
|
* to be extended one day...
|
|
*
|
|
* As an important side effect, pulling the storage into this template is
|
|
* enough obfuscation to confuse gcc's strict-aliasing analysis into not giving
|
|
* false negatives when we cast from the char buffer to whatever type we've
|
|
* constructed using the bytes.
|
|
*/
|
|
template<size_t nbytes>
|
|
struct AlignedStorage
|
|
{
|
|
union U {
|
|
char bytes[nbytes];
|
|
uint64_t _;
|
|
} u;
|
|
|
|
const void* addr() const { return u.bytes; }
|
|
void* addr() { return u.bytes; }
|
|
};
|
|
|
|
template<class T>
|
|
struct AlignedStorage2
|
|
{
|
|
union U {
|
|
char bytes[sizeof(T)];
|
|
uint64_t _;
|
|
} u;
|
|
|
|
const T* addr() const { return reinterpret_cast<const T*>(u.bytes); }
|
|
T* addr() { return static_cast<T*>(static_cast<void*>(u.bytes)); }
|
|
};
|
|
|
|
/*
|
|
* Small utility for lazily constructing objects without using dynamic storage.
|
|
* When a Maybe<T> is constructed, it is |empty()|, i.e., no value of T has
|
|
* been constructed and no T destructor will be called when the Maybe<T> is
|
|
* destroyed. Upon calling |construct|, a T object will be constructed with the
|
|
* given arguments and that object will be destroyed when the owning Maybe<T>
|
|
* is destroyed.
|
|
*
|
|
* N.B. GCC seems to miss some optimizations with Maybe and may generate extra
|
|
* branches/loads/stores. Use with caution on hot paths.
|
|
*/
|
|
template<class T>
|
|
class Maybe
|
|
{
|
|
AlignedStorage2<T> storage;
|
|
bool constructed;
|
|
|
|
T& asT() { return *storage.addr(); }
|
|
|
|
public:
|
|
Maybe() { constructed = false; }
|
|
~Maybe() { if (constructed) asT().~T(); }
|
|
|
|
bool empty() const { return !constructed; }
|
|
|
|
void construct() {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T();
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1>
|
|
void construct(const T1& t1) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1);
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1, class T2>
|
|
void construct(const T1& t1, const T2& t2) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1, t2);
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1, class T2, class T3>
|
|
void construct(const T1& t1, const T2& t2, const T3& t3) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1, t2, t3);
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1, class T2, class T3, class T4>
|
|
void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1, t2, t3, t4);
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1, class T2, class T3, class T4, class T5>
|
|
void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1, t2, t3, t4, t5);
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1, class T2, class T3, class T4, class T5,
|
|
class T6>
|
|
void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
|
|
const T6& t6) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1, t2, t3, t4, t5, t6);
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1, class T2, class T3, class T4, class T5,
|
|
class T6, class T7>
|
|
void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
|
|
const T6& t6, const T7& t7) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7);
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1, class T2, class T3, class T4, class T5,
|
|
class T6, class T7, class T8>
|
|
void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
|
|
const T6& t6, const T7& t7, const T8& t8) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7, t8);
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1, class T2, class T3, class T4, class T5,
|
|
class T6, class T7, class T8, class T9>
|
|
void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
|
|
const T6& t6, const T7& t7, const T8& t8, const T9& t9) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7, t8, t9);
|
|
constructed = true;
|
|
}
|
|
|
|
template<class T1, class T2, class T3, class T4, class T5,
|
|
class T6, class T7, class T8, class T9, class T10>
|
|
void construct(const T1& t1, const T2& t2, const T3& t3, const T4& t4, const T5& t5,
|
|
const T6& t6, const T7& t7, const T8& t8, const T9& t9, const T10& t10) {
|
|
MOZ_ASSERT(!constructed);
|
|
::new (storage.addr()) T(t1, t2, t3, t4, t5, t6, t7, t8, t9, t10);
|
|
constructed = true;
|
|
}
|
|
|
|
T* addr() {
|
|
MOZ_ASSERT(constructed);
|
|
return &asT();
|
|
}
|
|
|
|
T& ref() {
|
|
MOZ_ASSERT(constructed);
|
|
return asT();
|
|
}
|
|
|
|
const T& ref() const {
|
|
MOZ_ASSERT(constructed);
|
|
return const_cast<Maybe*>(this)->asT();
|
|
}
|
|
|
|
void destroy() {
|
|
ref().~T();
|
|
constructed = false;
|
|
}
|
|
|
|
void destroyIfConstructed() {
|
|
if (!empty())
|
|
destroy();
|
|
}
|
|
|
|
private:
|
|
Maybe(const Maybe& other) MOZ_DELETE;
|
|
const Maybe& operator=(const Maybe& other) MOZ_DELETE;
|
|
};
|
|
|
|
/*
|
|
* Safely subtract two pointers when it is known that end >= begin. This avoids
|
|
* the common compiler bug that if (size_t(end) - size_t(begin)) has the MSB
|
|
* set, the unsigned subtraction followed by right shift will produce -1, or
|
|
* size_t(-1), instead of the real difference.
|
|
*/
|
|
template<class T>
|
|
MOZ_ALWAYS_INLINE size_t
|
|
PointerRangeSize(T* begin, T* end)
|
|
{
|
|
MOZ_ASSERT(end >= begin);
|
|
return (size_t(end) - size_t(begin)) / sizeof(T);
|
|
}
|
|
|
|
/*
|
|
* Compute the length of an array with constant length. (Use of this method
|
|
* with a non-array pointer will not compile.)
|
|
*
|
|
* Beware of the implicit trailing '\0' when using this with string constants.
|
|
*/
|
|
template<typename T, size_t N>
|
|
MOZ_CONSTEXPR size_t
|
|
ArrayLength(T (&arr)[N])
|
|
{
|
|
return N;
|
|
}
|
|
|
|
/*
|
|
* Compute the address one past the last element of a constant-length array.
|
|
*
|
|
* Beware of the implicit trailing '\0' when using this with string constants.
|
|
*/
|
|
template<typename T, size_t N>
|
|
MOZ_CONSTEXPR T*
|
|
ArrayEnd(T (&arr)[N])
|
|
{
|
|
return arr + ArrayLength(arr);
|
|
}
|
|
|
|
} /* namespace mozilla */
|
|
|
|
#endif /* __cplusplus */
|
|
|
|
/*
|
|
* MOZ_ARRAY_LENGTH() is an alternative to mozilla::ArrayLength() for C files
|
|
* that can't use C++ template functions and for MOZ_STATIC_ASSERT() calls that
|
|
* can't call ArrayLength() when it is not a C++11 constexpr function.
|
|
*/
|
|
#ifdef MOZ_HAVE_CXX11_CONSTEXPR
|
|
# define MOZ_ARRAY_LENGTH(array) mozilla::ArrayLength(array)
|
|
#else
|
|
# define MOZ_ARRAY_LENGTH(array) (sizeof(array)/sizeof((array)[0]))
|
|
#endif
|
|
|
|
#endif /* mozilla_Util_h_ */
|