mirror of
https://github.com/mozilla/gecko-dev.git
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281 lines
6.7 KiB
C++
281 lines
6.7 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/*
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* Implements a smart pointer asserted to remain within a range specified at
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* construction.
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*/
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#ifndef mozilla_RangedPtr_h
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#define mozilla_RangedPtr_h
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#include "mozilla/ArrayUtils.h"
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#include "mozilla/Assertions.h"
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#include "mozilla/Attributes.h"
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#include <stdint.h>
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namespace mozilla {
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/*
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* RangedPtr is a smart pointer restricted to an address range specified at
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* creation. The pointer (and any smart pointers derived from it) must remain
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* within the range [start, end] (inclusive of end to facilitate use as
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* sentinels). Dereferencing or indexing into the pointer (or pointers derived
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* from it) must remain within the range [start, end). All the standard pointer
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* operators are defined on it; in debug builds these operations assert that the
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* range specified at construction is respected.
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*
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* In theory passing a smart pointer instance as an argument can be slightly
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* slower than passing a T* (due to ABI requirements for passing structs versus
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* passing pointers), if the method being called isn't inlined. If you are in
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* extremely performance-critical code, you may want to be careful using this
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* smart pointer as an argument type.
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*
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* RangedPtr<T> intentionally does not implicitly convert to T*. Use get() to
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* explicitly convert to T*. Keep in mind that the raw pointer of course won't
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* implement bounds checking in debug builds.
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*/
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template<typename T>
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class RangedPtr
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{
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T* mPtr;
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#ifdef DEBUG
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T* const mRangeStart;
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T* const mRangeEnd;
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#endif
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void checkSanity()
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{
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MOZ_ASSERT(mRangeStart <= mPtr);
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MOZ_ASSERT(mPtr <= mRangeEnd);
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}
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/* Creates a new pointer for |aPtr|, restricted to this pointer's range. */
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RangedPtr<T> create(T* aPtr) const
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{
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#ifdef DEBUG
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return RangedPtr<T>(aPtr, mRangeStart, mRangeEnd);
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#else
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return RangedPtr<T>(aPtr, nullptr, size_t(0));
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#endif
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}
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uintptr_t asUintptr() const { return reinterpret_cast<uintptr_t>(mPtr); }
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public:
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RangedPtr(T* aPtr, T* aStart, T* aEnd)
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: mPtr(aPtr)
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#ifdef DEBUG
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, mRangeStart(aStart), mRangeEnd(aEnd)
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#endif
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{
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MOZ_ASSERT(mRangeStart <= mRangeEnd);
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checkSanity();
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}
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RangedPtr(T* aPtr, T* aStart, size_t aLength)
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: mPtr(aPtr)
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#ifdef DEBUG
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, mRangeStart(aStart), mRangeEnd(aStart + aLength)
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#endif
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{
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MOZ_ASSERT(aLength <= size_t(-1) / sizeof(T));
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MOZ_ASSERT(reinterpret_cast<uintptr_t>(mRangeStart) + aLength * sizeof(T) >=
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reinterpret_cast<uintptr_t>(mRangeStart));
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checkSanity();
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}
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/* Equivalent to RangedPtr(aPtr, aPtr, aLength). */
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RangedPtr(T* aPtr, size_t aLength)
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: mPtr(aPtr)
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#ifdef DEBUG
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, mRangeStart(aPtr), mRangeEnd(aPtr + aLength)
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#endif
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{
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MOZ_ASSERT(aLength <= size_t(-1) / sizeof(T));
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MOZ_ASSERT(reinterpret_cast<uintptr_t>(mRangeStart) + aLength * sizeof(T) >=
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reinterpret_cast<uintptr_t>(mRangeStart));
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checkSanity();
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}
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/* Equivalent to RangedPtr(aArr, aArr, N). */
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template<size_t N>
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explicit RangedPtr(T (&aArr)[N])
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: mPtr(aArr)
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#ifdef DEBUG
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, mRangeStart(aArr), mRangeEnd(aArr + N)
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#endif
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{
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checkSanity();
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}
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T* get() const { return mPtr; }
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explicit operator bool() const { return mPtr != nullptr; }
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/*
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* You can only assign one RangedPtr into another if the two pointers have
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* the same valid range:
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*
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* char arr1[] = "hi";
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* char arr2[] = "bye";
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* RangedPtr<char> p1(arr1, 2);
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* p1 = RangedPtr<char>(arr1 + 1, arr1, arr1 + 2); // works
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* p1 = RangedPtr<char>(arr2, 3); // asserts
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*/
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RangedPtr<T>& operator=(const RangedPtr<T>& aOther)
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{
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MOZ_ASSERT(mRangeStart == aOther.mRangeStart);
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MOZ_ASSERT(mRangeEnd == aOther.mRangeEnd);
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mPtr = aOther.mPtr;
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checkSanity();
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return *this;
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}
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RangedPtr<T> operator+(size_t aInc)
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{
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MOZ_ASSERT(aInc <= size_t(-1) / sizeof(T));
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MOZ_ASSERT(asUintptr() + aInc * sizeof(T) >= asUintptr());
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return create(mPtr + aInc);
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}
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RangedPtr<T> operator-(size_t aDec)
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{
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MOZ_ASSERT(aDec <= size_t(-1) / sizeof(T));
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MOZ_ASSERT(asUintptr() - aDec * sizeof(T) <= asUintptr());
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return create(mPtr - aDec);
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}
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/*
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* You can assign a raw pointer into a RangedPtr if the raw pointer is
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* within the range specified at creation.
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*/
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template <typename U>
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RangedPtr<T>& operator=(U* aPtr)
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{
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*this = create(aPtr);
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return *this;
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}
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template <typename U>
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RangedPtr<T>& operator=(const RangedPtr<U>& aPtr)
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{
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MOZ_ASSERT(mRangeStart <= aPtr.mPtr);
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MOZ_ASSERT(aPtr.mPtr <= mRangeEnd);
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mPtr = aPtr.mPtr;
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checkSanity();
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return *this;
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}
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RangedPtr<T>& operator++()
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{
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return (*this += 1);
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}
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RangedPtr<T> operator++(int)
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{
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RangedPtr<T> rcp = *this;
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++*this;
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return rcp;
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}
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RangedPtr<T>& operator--()
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{
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return (*this -= 1);
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}
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RangedPtr<T> operator--(int)
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{
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RangedPtr<T> rcp = *this;
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--*this;
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return rcp;
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}
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RangedPtr<T>& operator+=(size_t aInc)
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{
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*this = *this + aInc;
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return *this;
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}
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RangedPtr<T>& operator-=(size_t aDec)
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{
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*this = *this - aDec;
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return *this;
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}
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T& operator[](int aIndex) const
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{
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MOZ_ASSERT(size_t(aIndex > 0 ? aIndex : -aIndex) <= size_t(-1) / sizeof(T));
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return *create(mPtr + aIndex);
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}
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T& operator*() const
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{
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MOZ_ASSERT(mPtr >= mRangeStart);
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MOZ_ASSERT(mPtr < mRangeEnd);
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return *mPtr;
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}
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template <typename U>
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bool operator==(const RangedPtr<U>& aOther) const
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{
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return mPtr == aOther.mPtr;
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}
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template <typename U>
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bool operator!=(const RangedPtr<U>& aOther) const
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{
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return !(*this == aOther);
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}
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template<typename U>
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bool operator==(const U* u) const
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{
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return mPtr == u;
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}
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template<typename U>
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bool operator!=(const U* u) const
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{
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return !(*this == u);
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}
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template <typename U>
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bool operator<(const RangedPtr<U>& aOther) const
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{
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return mPtr < aOther.mPtr;
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}
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template <typename U>
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bool operator<=(const RangedPtr<U>& aOther) const
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{
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return mPtr <= aOther.mPtr;
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}
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template <typename U>
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bool operator>(const RangedPtr<U>& aOther) const
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{
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return mPtr > aOther.mPtr;
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}
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template <typename U>
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bool operator>=(const RangedPtr<U>& aOther) const
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{
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return mPtr >= aOther.mPtr;
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}
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size_t operator-(const RangedPtr<T>& aOther) const
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{
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MOZ_ASSERT(mPtr >= aOther.mPtr);
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return PointerRangeSize(aOther.mPtr, mPtr);
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}
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private:
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RangedPtr() = delete;
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T* operator&() = delete;
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};
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} /* namespace mozilla */
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#endif /* mozilla_RangedPtr_h */
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