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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 "mozilla/NullPtr.h"

 #include <stdint.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 {

       MOZ_ASSERT(ptr >= rangeStart);

       MOZ_ASSERT(ptr < rangeEnd);

       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 */