mfbt/RangedPtr.h
author Narcis Beleuzu <nbeleuzu@mozilla.com>
Thu, 21 Jun 2018 16:51:55 +0300
changeset 477502 59322b179c0fdb4423d42b624da7bf64ee5a2327
parent 371524 e70365b0720ce124090edf22adeeee0935dbf433
child 479670 b982fcdb2ded44272f2c08be9579b59fd2406364
permissions -rw-r--r--
Backed out 4 changesets (bug 1268889) for Windows GTest failures. CLOSED TREE Backed out changeset da427a67372e (bug 1268889) Backed out changeset 97528847b7b7 (bug 1268889) Backed out changeset b2320061fbcb (bug 1268889) Backed out changeset dd3b7047ea6f (bug 1268889)

/* -*- 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>

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* 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();
  }

  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);
  }

  /*
   * 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[](int 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);
  }

  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 */