mirror of
https://github.com/mozilla/gecko-dev.git
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255 lines
6.7 KiB
C++
255 lines
6.7 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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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/Assertions.h"
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#include "mozilla/Attributes.h"
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#include "mozilla/Util.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* ptr;
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#ifdef DEBUG
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T* const rangeStart;
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T* const rangeEnd;
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#endif
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typedef void (RangedPtr::* ConvertibleToBool)();
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void nonNull() {}
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void checkSanity() {
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MOZ_ASSERT(rangeStart <= ptr);
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MOZ_ASSERT(ptr <= rangeEnd);
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}
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/* Creates a new pointer for |p|, restricted to this pointer's range. */
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RangedPtr<T> create(T *p) const {
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#ifdef DEBUG
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return RangedPtr<T>(p, rangeStart, rangeEnd);
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#else
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return RangedPtr<T>(p, NULL, size_t(0));
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#endif
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}
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uintptr_t asUintptr() const { return uintptr_t(ptr); }
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public:
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RangedPtr(T* p, T* start, T* end)
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: ptr(p)
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#ifdef DEBUG
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, rangeStart(start), rangeEnd(end)
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#endif
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{
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MOZ_ASSERT(rangeStart <= rangeEnd);
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checkSanity();
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}
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RangedPtr(T* p, T* start, size_t length)
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: ptr(p)
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#ifdef DEBUG
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, rangeStart(start), rangeEnd(start + length)
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#endif
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{
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MOZ_ASSERT(length <= size_t(-1) / sizeof(T));
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MOZ_ASSERT(uintptr_t(rangeStart) + length * sizeof(T) >= uintptr_t(rangeStart));
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checkSanity();
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}
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/* Equivalent to RangedPtr(p, p, length). */
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RangedPtr(T* p, size_t length)
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: ptr(p)
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#ifdef DEBUG
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, rangeStart(p), rangeEnd(p + length)
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#endif
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{
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MOZ_ASSERT(length <= size_t(-1) / sizeof(T));
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MOZ_ASSERT(uintptr_t(rangeStart) + length * sizeof(T) >= uintptr_t(rangeStart));
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checkSanity();
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}
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/* Equivalent to RangedPtr(arr, arr, N). */
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template<size_t N>
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RangedPtr(T (&arr)[N])
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: ptr(arr)
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#ifdef DEBUG
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, rangeStart(arr), rangeEnd(arr + 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 {
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return ptr;
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}
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operator ConvertibleToBool() const { return ptr ? &RangedPtr::nonNull : 0; }
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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>& other) {
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MOZ_ASSERT(rangeStart == other.rangeStart);
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MOZ_ASSERT(rangeEnd == other.rangeEnd);
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ptr = other.ptr;
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checkSanity();
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return *this;
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}
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RangedPtr<T> operator+(size_t inc) {
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MOZ_ASSERT(inc <= size_t(-1) / sizeof(T));
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MOZ_ASSERT(asUintptr() + inc * sizeof(T) >= asUintptr());
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return create(ptr + inc);
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}
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RangedPtr<T> operator-(size_t dec) {
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MOZ_ASSERT(dec <= size_t(-1) / sizeof(T));
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MOZ_ASSERT(asUintptr() - dec * sizeof(T) <= asUintptr());
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return create(ptr - dec);
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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* p) {
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*this = create(p);
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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>& p) {
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MOZ_ASSERT(rangeStart <= p.ptr);
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MOZ_ASSERT(p.ptr <= rangeEnd);
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ptr = p.ptr;
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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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return (*this += 1);
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}
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RangedPtr<T> operator++(int) {
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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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return (*this -= 1);
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}
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RangedPtr<T> operator--(int) {
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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 inc) {
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*this = *this + inc;
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return *this;
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}
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RangedPtr<T>& operator-=(size_t dec) {
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*this = *this - dec;
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return *this;
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}
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T& operator[](int index) const {
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MOZ_ASSERT(size_t(index > 0 ? index : -index) <= size_t(-1) / sizeof(T));
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return *create(ptr + index);
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}
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T& operator*() const {
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return *ptr;
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}
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template <typename U>
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bool operator==(const RangedPtr<U>& other) const {
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return ptr == other.ptr;
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}
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template <typename U>
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bool operator!=(const RangedPtr<U>& other) const {
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return !(*this == other);
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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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return ptr == 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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return !(*this == u);
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}
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template <typename U>
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bool operator<(const RangedPtr<U>& other) const {
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return ptr < other.ptr;
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}
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template <typename U>
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bool operator<=(const RangedPtr<U>& other) const {
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return ptr <= other.ptr;
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}
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template <typename U>
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bool operator>(const RangedPtr<U>& other) const {
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return ptr > other.ptr;
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}
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template <typename U>
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bool operator>=(const RangedPtr<U>& other) const {
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return ptr >= other.ptr;
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}
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size_t operator-(const RangedPtr<T>& other) const {
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MOZ_ASSERT(ptr >= other.ptr);
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return PointerRangeSize(other.ptr, ptr);
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}
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private:
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RangedPtr() MOZ_DELETE;
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T* operator&() MOZ_DELETE;
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};
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} /* namespace mozilla */
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#endif /* mozilla_RangedPtr_h_ */
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