gecko-dev/mfbt/RangedPtr.h

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C
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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
2012-05-21 15:12:37 +04:00
* 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/. */
/*
* Implements a smart pointer asserted to remain within a range specified at
* construction.
*/
#ifndef mozilla_RangedPtr_h
#define mozilla_RangedPtr_h
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/NullPtr.h"
#include "mozilla/Util.h"
namespace mozilla {
/*
* RangedPtr is a smart pointer restricted to an address range specified at
* creation. The pointer (and any smart pointers derived from it) must remain
* within the range [start, end] (inclusive of end to facilitate use as
* sentinels). Dereferencing or indexing into the pointer (or pointers derived
* from it) must remain within the range [start, end). All the standard pointer
* operators are defined on it; in debug builds these operations assert that the
* range specified at construction is respected.
*
* In theory passing a smart pointer instance as an argument can be slightly
* slower than passing a T* (due to ABI requirements for passing structs versus
* passing pointers), if the method being called isn't inlined. If you are in
* extremely performance-critical code, you may want to be careful using this
* smart pointer as an argument type.
*
* RangedPtr<T> intentionally does not implicitly convert to T*. Use get() to
* explicitly convert to T*. Keep in mind that the raw pointer of course won't
* implement bounds checking in debug builds.
*/
template<typename T>
class RangedPtr
{
T* ptr;
#ifdef DEBUG
T* const rangeStart;
T* const rangeEnd;
#endif
typedef void (RangedPtr::* ConvertibleToBool)();
void nonNull() {}
void checkSanity() {
MOZ_ASSERT(rangeStart <= ptr);
MOZ_ASSERT(ptr <= rangeEnd);
}
/* Creates a new pointer for |p|, restricted to this pointer's range. */
RangedPtr<T> create(T *p) const {
#ifdef DEBUG
return RangedPtr<T>(p, rangeStart, rangeEnd);
#else
return RangedPtr<T>(p, nullptr, size_t(0));
#endif
}
uintptr_t asUintptr() const { return uintptr_t(ptr); }
public:
RangedPtr(T* p, T* start, T* end)
: ptr(p)
#ifdef DEBUG
, rangeStart(start), rangeEnd(end)
#endif
{
MOZ_ASSERT(rangeStart <= rangeEnd);
checkSanity();
}
RangedPtr(T* p, T* start, size_t length)
: ptr(p)
#ifdef DEBUG
, rangeStart(start), rangeEnd(start + length)
#endif
{
MOZ_ASSERT(length <= size_t(-1) / sizeof(T));
MOZ_ASSERT(uintptr_t(rangeStart) + length * sizeof(T) >= uintptr_t(rangeStart));
checkSanity();
}
/* Equivalent to RangedPtr(p, p, length). */
RangedPtr(T* p, size_t length)
: ptr(p)
#ifdef DEBUG
, rangeStart(p), rangeEnd(p + length)
#endif
{
MOZ_ASSERT(length <= size_t(-1) / sizeof(T));
MOZ_ASSERT(uintptr_t(rangeStart) + length * sizeof(T) >= uintptr_t(rangeStart));
checkSanity();
}
/* Equivalent to RangedPtr(arr, arr, N). */
template<size_t N>
RangedPtr(T (&arr)[N])
: ptr(arr)
#ifdef DEBUG
, rangeStart(arr), rangeEnd(arr + N)
#endif
{
checkSanity();
}
T* get() const {
return ptr;
}
operator ConvertibleToBool() const { return ptr ? &RangedPtr::nonNull : 0; }
/*
* You can only assign one RangedPtr into another if the two pointers have
* the same valid range:
*
* char arr1[] = "hi";
* char arr2[] = "bye";
* RangedPtr<char> p1(arr1, 2);
* p1 = RangedPtr<char>(arr1 + 1, arr1, arr1 + 2); // works
* p1 = RangedPtr<char>(arr2, 3); // asserts
*/
RangedPtr<T>& operator=(const RangedPtr<T>& other) {
MOZ_ASSERT(rangeStart == other.rangeStart);
MOZ_ASSERT(rangeEnd == other.rangeEnd);
ptr = other.ptr;
checkSanity();
return *this;
}
RangedPtr<T> operator+(size_t inc) {
MOZ_ASSERT(inc <= size_t(-1) / sizeof(T));
MOZ_ASSERT(asUintptr() + inc * sizeof(T) >= asUintptr());
return create(ptr + inc);
}
RangedPtr<T> operator-(size_t dec) {
MOZ_ASSERT(dec <= size_t(-1) / sizeof(T));
MOZ_ASSERT(asUintptr() - dec * sizeof(T) <= asUintptr());
return create(ptr - dec);
}
/*
* You can assign a raw pointer into a RangedPtr if the raw pointer is
* within the range specified at creation.
*/
template <typename U>
RangedPtr<T>& operator=(U* p) {
*this = create(p);
return *this;
}
template <typename U>
RangedPtr<T>& operator=(const RangedPtr<U>& p) {
MOZ_ASSERT(rangeStart <= p.ptr);
MOZ_ASSERT(p.ptr <= rangeEnd);
ptr = p.ptr;
checkSanity();
return *this;
}
RangedPtr<T>& operator++() {
return (*this += 1);
}
RangedPtr<T> operator++(int) {
RangedPtr<T> rcp = *this;
++*this;
return rcp;
}
RangedPtr<T>& operator--() {
return (*this -= 1);
}
RangedPtr<T> operator--(int) {
RangedPtr<T> rcp = *this;
--*this;
return rcp;
}
RangedPtr<T>& operator+=(size_t inc) {
*this = *this + inc;
return *this;
}
RangedPtr<T>& operator-=(size_t dec) {
*this = *this - dec;
return *this;
}
T& operator[](int index) const {
MOZ_ASSERT(size_t(index > 0 ? index : -index) <= size_t(-1) / sizeof(T));
return *create(ptr + index);
}
T& operator*() const {
return *ptr;
}
template <typename U>
bool operator==(const RangedPtr<U>& other) const {
return ptr == other.ptr;
}
template <typename U>
bool operator!=(const RangedPtr<U>& other) const {
return !(*this == other);
}
template<typename U>
bool operator==(const U* u) const {
return ptr == u;
}
template<typename U>
bool operator!=(const U* u) const {
return !(*this == u);
}
template <typename U>
bool operator<(const RangedPtr<U>& other) const {
return ptr < other.ptr;
}
template <typename U>
bool operator<=(const RangedPtr<U>& other) const {
return ptr <= other.ptr;
}
template <typename U>
bool operator>(const RangedPtr<U>& other) const {
return ptr > other.ptr;
}
template <typename U>
bool operator>=(const RangedPtr<U>& other) const {
return ptr >= other.ptr;
}
size_t operator-(const RangedPtr<T>& other) const {
MOZ_ASSERT(ptr >= other.ptr);
return PointerRangeSize(other.ptr, ptr);
}
private:
RangedPtr() MOZ_DELETE;
T* operator&() MOZ_DELETE;
};
} /* namespace mozilla */
#endif /* mozilla_RangedPtr_h */