diff options
Diffstat (limited to 'mfbt/RangedPtr.h')
| -rw-r--r-- | mfbt/RangedPtr.h | 308 |
1 files changed, 308 insertions, 0 deletions
diff --git a/mfbt/RangedPtr.h b/mfbt/RangedPtr.h new file mode 100644 index 0000000000..9aec59f936 --- /dev/null +++ b/mfbt/RangedPtr.h @@ -0,0 +1,308 @@ +/* -*- 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 */ |