mfbt/Buffer.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef mozilla_Buffer_h
   6 #define mozilla_Buffer_h
   7
   8 #include <algorithm>
   9 #include <iterator>
  10
  11 #include "mozilla/Maybe.h"
  12 #include "mozilla/Span.h"
  13 #include "mozilla/UniquePtr.h"
  14 #include "mozilla/UniquePtrExtensions.h"
  15
  16 namespace mozilla {
  17
  18 /**
  19  * A move-only type that wraps a mozilla::UniquePtr<T[]> and the length of
  20  * the T[].
  21  *
  22  * Unlike mozilla::Array, the length is a run-time property.
  23  * Unlike mozilla::Vector and nsTArray, does not have capacity and
  24  * assocatiated growth functionality.
  25  * Unlike mozilla::Span, mozilla::Buffer owns the allocation it points to.
  26  */
  27 template <typename T>
  28 class Buffer final {
  29  private:
  30   mozilla::UniquePtr<T[]> mData;
  31   size_t mLength;
  32
  33  public:
  34   Buffer(const Buffer<T>& aOther) = delete;
  35   Buffer<T>& operator=(const Buffer<T>& aOther) = delete;
  36
  37   /**
  38    * Construct zero-lenth Buffer (without actually pointing to a heap
  39    * allocation).
  40    */
  41   Buffer() : mData(nullptr), mLength(0){};
  42
  43   /**
  44    * Construct from raw parts.
  45    *
  46    * aLength must not be greater than the actual length of the buffer pointed
  47    * to by aData.
  48    */
  49   Buffer(mozilla::UniquePtr<T[]>&& aData, size_t aLength)
  50       : mData(std::move(aData)), mLength(aLength) {}
  51
  52   /**
  53    * Move constructor. Sets the moved-from Buffer to zero-length
  54    * state.
  55    */
  56   Buffer(Buffer<T>&& aOther)
  57       : mData(std::move(aOther.mData)), mLength(aOther.mLength) {
  58     aOther.mLength = 0;
  59   }
  60
  61   /**
  62    * Move assignment. Sets the moved-from Buffer to zero-length
  63    * state.
  64    */
  65   Buffer<T>& operator=(Buffer<T>&& aOther) {
  66     mData = std::move(aOther.mData);
  67     mLength = aOther.mLength;
  68     aOther.mLength = 0;
  69     return *this;
  70   }
  71
  72   /**
  73    * Construct by copying the elements of a Span.
  74    *
  75    * Allocates the internal buffer infallibly. Use CopyFrom for fallible
  76    * allocation.
  77    */
  78   explicit Buffer(mozilla::Span<const T> aSpan)
  79       : mData(mozilla::MakeUniqueForOverwrite<T[]>(aSpan.Length())),
  80         mLength(aSpan.Length()) {
  81     std::copy(aSpan.cbegin(), aSpan.cend(), mData.get());
  82   }
  83
  84   /**
  85    * Create a new Buffer by copying the elements of a Span.
  86    *
  87    * Allocates the internal buffer fallibly.
  88    */
  89   static mozilla::Maybe<Buffer<T>> CopyFrom(mozilla::Span<const T> aSpan) {
  90     if (aSpan.IsEmpty()) {
  91       return Some(Buffer());
  92     }
  93
  94     auto data = mozilla::MakeUniqueForOverwriteFallible<T[]>(aSpan.Length());
  95     if (!data) {
  96       return mozilla::Nothing();
  97     }
  98     std::copy(aSpan.cbegin(), aSpan.cend(), data.get());
  99     return mozilla::Some(Buffer(std::move(data), aSpan.Length()));
 100   }
 101
 102   /**
 103    * Construct a buffer of requested length.
 104    *
 105    * The contents will be initialized or uninitialized according
 106    * to the behavior of mozilla::MakeUnique<T[]>(aLength) for T.
 107    *
 108    * Allocates the internal buffer infallibly. Use Alloc for fallible
 109    * allocation.
 110    */
 111   explicit Buffer(size_t aLength)
 112       : mData(mozilla::MakeUnique<T[]>(aLength)), mLength(aLength) {}
 113
 114   /**
 115    * Create a new Buffer with an internal buffer of requested length.
 116    *
 117    * The contents will be initialized or uninitialized according to the
 118    * behavior of mozilla::MakeUnique<T[]>(aLength) for T.
 119    *
 120    * Allocates the internal buffer fallibly.
 121    */
 122   static mozilla::Maybe<Buffer<T>> Alloc(size_t aLength) {
 123     auto data = mozilla::MakeUniqueFallible<T[]>(aLength);
 124     if (!data) {
 125       return mozilla::Nothing();
 126     }
 127     return mozilla::Some(Buffer(std::move(data), aLength));
 128   }
 129
 130   /**
 131    * Create a new Buffer with an internal buffer of requested length.
 132    *
 133    * This uses MakeUniqueFallibleForOverwrite so the contents will be
 134    * default-initialized.
 135    *
 136    * Allocates the internal buffer fallibly.
 137    */
 138   static Maybe<Buffer<T>> AllocForOverwrite(size_t aLength) {
 139     auto data = MakeUniqueForOverwriteFallible<T[]>(aLength);
 140     if (!data) {
 141       return Nothing();
 142     }
 143     return Some(Buffer(std::move(data), aLength));
 144   }
 145
 146   auto AsSpan() const { return mozilla::Span<const T>{mData.get(), mLength}; }
 147   auto AsWritableSpan() { return mozilla::Span<T>{mData.get(), mLength}; }
 148   operator mozilla::Span<const T>() const { return AsSpan(); }
 149   operator mozilla::Span<T>() { return AsWritableSpan(); }
 150
 151   /**
 152    * Guarantees a non-null and aligned pointer
 153    * even for the zero-length case.
 154    */
 155   T* Elements() { return AsWritableSpan().Elements(); }
 156   size_t Length() const { return mLength; }
 157
 158   T& operator[](size_t aIndex) {
 159     MOZ_ASSERT(aIndex < mLength);
 160     return mData.get()[aIndex];
 161   }
 162
 163   const T& operator[](size_t aIndex) const {
 164     MOZ_ASSERT(aIndex < mLength);
 165     return mData.get()[aIndex];
 166   }
 167
 168   typedef T* iterator;
 169   typedef const T* const_iterator;
 170   typedef std::reverse_iterator<T*> reverse_iterator;
 171   typedef std::reverse_iterator<const T*> const_reverse_iterator;
 172
 173   // Methods for range-based for loops.
 174   iterator begin() { return mData.get(); }
 175   const_iterator begin() const { return mData.get(); }
 176   const_iterator cbegin() const { return begin(); }
 177   iterator end() { return mData.get() + mLength; }
 178   const_iterator end() const { return mData.get() + mLength; }
 179   const_iterator cend() const { return end(); }
 180
 181   // Methods for reverse iterating.
 182   reverse_iterator rbegin() { return reverse_iterator(end()); }
 183   const_reverse_iterator rbegin() const {
 184     return const_reverse_iterator(end());
 185   }
 186   const_reverse_iterator crbegin() const { return rbegin(); }
 187   reverse_iterator rend() { return reverse_iterator(begin()); }
 188   const_reverse_iterator rend() const {
 189     return const_reverse_iterator(begin());
 190   }
 191   const_reverse_iterator crend() const { return rend(); }
 192 };
 193
 194 } /* namespace mozilla */
 195
 196 #endif /* mozilla_Buffer_h */