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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
* 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/ArrayUtils.h"
#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include <stdint.h>
#include <cstddef>
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 {
template <typename U>
friend class RangedPtr;
T* mPtr;
#ifdef DEBUG
T* const mRangeStart;
T* const mRangeEnd;
#endif
void checkSanity() {
MOZ_ASSERT(mRangeStart <= mPtr);
MOZ_ASSERT(mPtr <= mRangeEnd);
}
/* Creates a new pointer for |aPtr|, restricted to this pointer's range. */
RangedPtr<T> create(T* aPtr) const {
#ifdef DEBUG
return RangedPtr<T>(aPtr, mRangeStart, mRangeEnd);
#else
return RangedPtr<T>(aPtr, nullptr, size_t(0));
#endif
}
uintptr_t asUintptr() const { return reinterpret_cast<uintptr_t>(mPtr); }
public:
RangedPtr(T* aPtr, T* aStart, T* aEnd)
: mPtr(aPtr)
#ifdef DEBUG
,
mRangeStart(aStart),
mRangeEnd(aEnd)
#endif
{
MOZ_ASSERT(mRangeStart <= mRangeEnd);
checkSanity();
}
RangedPtr(T* aPtr, T* aStart, size_t aLength)
: mPtr(aPtr)
#ifdef DEBUG
,
mRangeStart(aStart),
mRangeEnd(aStart + aLength)
#endif
{
MOZ_ASSERT(aLength <= size_t(-1) / sizeof(T));
MOZ_ASSERT(reinterpret_cast<uintptr_t>(mRangeStart) + aLength * sizeof(T) >=
reinterpret_cast<uintptr_t>(mRangeStart));
checkSanity();
}
/* Equivalent to RangedPtr(aPtr, aPtr, aLength). */
RangedPtr(T* aPtr, size_t aLength)
: mPtr(aPtr)
#ifdef DEBUG
,
mRangeStart(aPtr),
mRangeEnd(aPtr + aLength)
#endif
{
MOZ_ASSERT(aLength <= size_t(-1) / sizeof(T));
MOZ_ASSERT(reinterpret_cast<uintptr_t>(mRangeStart) + aLength * sizeof(T) >=
reinterpret_cast<uintptr_t>(mRangeStart));
checkSanity();
}
/* Equivalent to RangedPtr(aArr, aArr, N). */
template <size_t N>
explicit RangedPtr(T (&aArr)[N])
: mPtr(aArr)
#ifdef DEBUG
,
mRangeStart(aArr),
mRangeEnd(aArr + N)
#endif
{
checkSanity();
}
RangedPtr(const RangedPtr& aOther)
: mPtr(aOther.mPtr)
#ifdef DEBUG
,
mRangeStart(aOther.mRangeStart),
mRangeEnd(aOther.mRangeEnd)
#endif
{
checkSanity();
}
template <typename U>
MOZ_IMPLICIT RangedPtr(const RangedPtr<U>& aOther)
: mPtr(aOther.mPtr)
#ifdef DEBUG
,
mRangeStart(aOther.mRangeStart),
mRangeEnd(aOther.mRangeEnd)
#endif
{
checkSanity();
}
T* get() const { return mPtr; }
explicit operator bool() const { return mPtr != nullptr; }
void checkIdenticalRange(const RangedPtr<T>& aOther) const {
MOZ_ASSERT(mRangeStart == aOther.mRangeStart);
MOZ_ASSERT(mRangeEnd == aOther.mRangeEnd);
}
template <typename U>
RangedPtr<U> ReinterpretCast() const {
#ifdef DEBUG
return {reinterpret_cast<U*>(mPtr), reinterpret_cast<U*>(mRangeStart),
reinterpret_cast<U*>(mRangeEnd)};
#else
return {reinterpret_cast<U*>(mPtr), nullptr, nullptr};
#endif
}
/*
* 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>& aOther) {
checkIdenticalRange(aOther);
mPtr = aOther.mPtr;
checkSanity();
return *this;
}
RangedPtr<T> operator+(size_t aInc) const {
MOZ_ASSERT(aInc <= size_t(-1) / sizeof(T));
MOZ_ASSERT(asUintptr() + aInc * sizeof(T) >= asUintptr());
return create(mPtr + aInc);
}
RangedPtr<T> operator-(size_t aDec) const {
MOZ_ASSERT(aDec <= size_t(-1) / sizeof(T));
MOZ_ASSERT(asUintptr() - aDec * sizeof(T) <= asUintptr());
return create(mPtr - aDec);
}
/*
* 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* aPtr) {
*this = create(aPtr);
return *this;
}
template <typename U>
RangedPtr<T>& operator=(const RangedPtr<U>& aPtr) {
MOZ_ASSERT(mRangeStart <= aPtr.mPtr);
MOZ_ASSERT(aPtr.mPtr <= mRangeEnd);
mPtr = aPtr.mPtr;
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 aInc) {
*this = *this + aInc;
return *this;
}
RangedPtr<T>& operator-=(size_t aDec) {
*this = *this - aDec;
return *this;
}
T& operator[](ptrdiff_t aIndex) const {
MOZ_ASSERT(size_t(aIndex > 0 ? aIndex : -aIndex) <= size_t(-1) / sizeof(T));
return *create(mPtr + aIndex);
}
T& operator*() const {
MOZ_ASSERT(mPtr >= mRangeStart);
MOZ_ASSERT(mPtr < mRangeEnd);
return *mPtr;
}
T* operator->() const {
MOZ_ASSERT(mPtr >= mRangeStart);
MOZ_ASSERT(mPtr < mRangeEnd);
return mPtr;
}
template <typename U>
bool operator==(const RangedPtr<U>& aOther) const {
return mPtr == aOther.mPtr;
}
template <typename U>
bool operator!=(const RangedPtr<U>& aOther) const {
return !(*this == aOther);
}
template <typename U>
bool operator==(const U* u) const {
return mPtr == u;
}
template <typename U>
bool operator!=(const U* u) const {
return !(*this == u);
}
bool operator==(std::nullptr_t) const { return mPtr == nullptr; }
bool operator!=(std::nullptr_t) const { return mPtr != nullptr; }
template <typename U>
bool operator<(const RangedPtr<U>& aOther) const {
return mPtr < aOther.mPtr;
}
template <typename U>
bool operator<=(const RangedPtr<U>& aOther) const {
return mPtr <= aOther.mPtr;
}
template <typename U>
bool operator>(const RangedPtr<U>& aOther) const {
return mPtr > aOther.mPtr;
}
template <typename U>
bool operator>=(const RangedPtr<U>& aOther) const {
return mPtr >= aOther.mPtr;
}
size_t operator-(const RangedPtr<T>& aOther) const {
MOZ_ASSERT(mPtr >= aOther.mPtr);
return PointerRangeSize(aOther.mPtr, mPtr);
}
private:
RangedPtr() = delete;
};
} /* namespace mozilla */
#endif /* mozilla_RangedPtr_h */