Create BitFieldArray

Source/Core/Common/BitField.h

@@ -33,6 +33,7 @@
 
 #include <cstddef>
 #include <fmt/format.h>
+#include <iterator>
 #include <limits>
 #include <type_traits>
 
@@ -202,3 +203,305 @@ struct fmt::formatter<BitField<position, bits, T, S>>
     return m_formatter.format(bitfield.Value(), ctx);
   }
 };
+
+// Language limitations require the following to make these formattable
+// (formatter<BitFieldArray<position, bits, size, T>::Ref> is not legal)
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+class BitFieldArrayConstRef;
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+class BitFieldArrayRef;
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+class BitFieldArrayConstIterator;
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+class BitFieldArrayIterator;
+
+#pragma pack(1)
+template <std::size_t position, std::size_t bits, std::size_t size, typename T,
+          // StorageType is T for non-enum types and the underlying type of T if
+          // T is an enumeration. Note that T is wrapped within an enable_if in the
+          // former case to workaround compile errors which arise when using
+          // std::underlying_type<T>::type directly.
+          typename StorageType = typename std::conditional_t<
+              std::is_enum<T>::value, std::underlying_type<T>, std::enable_if<true, T>>::type>
+struct BitFieldArray
+{
+  using Ref = BitFieldArrayRef<position, bits, size, T, StorageType>;
+  using ConstRef = BitFieldArrayConstRef<position, bits, size, T, StorageType>;
+  using Iterator = BitFieldArrayIterator<position, bits, size, T, StorageType>;
+  using ConstIterator = BitFieldArrayConstIterator<position, bits, size, T, StorageType>;
+
+private:
+  // This constructor might be considered ambiguous:
+  // Would it initialize the storage or just the bitfield?
+  // Hence, delete it. Use the assignment operator to set bitfield values!
+  BitFieldArray(T val) = delete;
+
+public:
+  // Force default constructor to be created
+  // so that we can use this within unions
+  constexpr BitFieldArray() = default;
+
+// Visual Studio (as of VS2017) considers BitField to not be trivially
+// copyable if we delete this copy assignment operator.
+// https://developercommunity.visualstudio.com/content/problem/101208/c-compiler-is-overly-strict-regarding-whether-a-cl.html
+#ifndef _MSC_VER
+  // We explicitly delete the copy assignment operator here, because the
+  // default copy assignment would copy the full storage value, rather than
+  // just the bits relevant to this particular bit field.
+  // Ideally, we would just implement the copy assignment to copy only the
+  // relevant bits, but we're prevented from doing that because the savestate
+  // code expects that this class is trivially copyable.
+  BitFieldArray& operator=(const BitFieldArray&) = delete;
+#endif
+
+public:
+  constexpr std::size_t StartBit() const { return position; }
+  constexpr std::size_t NumBits() const { return bits; }
+  constexpr std::size_t Size() const { return size; }
+  constexpr std::size_t TotalNumBits() const { return bits * size; }
+
+  constexpr T Value(size_t index) const { return Value(std::is_signed<T>(), index); }
+  void SetValue(size_t index, T value)
+  {
+    const size_t pos = position + bits * index;
+    storage = (storage & ~GetElementMask(index)) |
+              ((static_cast<StorageType>(value) << pos) & GetElementMask(index));
+  }
+  Ref operator[](size_t index) { return Ref(this, index); }
+  constexpr const ConstRef operator[](size_t index) const { return ConstRef(this, index); }
+
+  constexpr Iterator begin() { return Iterator(this, 0); }
+  constexpr Iterator end() { return Iterator(this, size); }
+  constexpr ConstIterator begin() const { return ConstIterator(this, 0); }
+  constexpr ConstIterator end() const { return ConstIterator(this, size); }
+  constexpr ConstIterator cbegin() const { return begin(); }
+  constexpr ConstIterator cend() const { return end(); }
+
+private:
+  // Unsigned version of StorageType
+  using StorageTypeU = std::make_unsigned_t<StorageType>;
+
+  constexpr T Value(std::true_type, size_t index) const
+  {
+    const size_t pos = position + bits * index;
+    const size_t shift_amount = 8 * sizeof(StorageType) - bits;
+    return static_cast<T>((storage << (shift_amount - pos)) >> shift_amount);
+  }
+
+  constexpr T Value(std::false_type, size_t index) const
+  {
+    const size_t pos = position + bits * index;
+    return static_cast<T>((storage & GetElementMask(index)) >> pos);
+  }
+
+  static constexpr StorageType GetElementMask(size_t index)
+  {
+    const size_t pos = position + bits * index;
+    return (std::numeric_limits<StorageTypeU>::max() >> (8 * sizeof(StorageType) - bits)) << pos;
+  }
+
+  StorageType storage;
+
+  static_assert(bits * size + position <= 8 * sizeof(StorageType), "Bitfield array out of range");
+  static_assert(sizeof(T) <= sizeof(StorageType), "T must fit in StorageType");
+
+  // And, you know, just in case people specify something stupid like bits=position=0x80000000
+  static_assert(position < 8 * sizeof(StorageType), "Invalid position");
+  static_assert(bits <= 8 * sizeof(T), "Invalid number of bits");
+  static_assert(bits > 0, "Invalid number of bits");
+  static_assert(size <= 8 * sizeof(StorageType), "Invalid size");
+  static_assert(size > 0, "Invalid size");
+};
+#pragma pack()
+
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+class BitFieldArrayConstRef
+{
+  friend struct BitFieldArray<position, bits, size, T, S>;
+  friend class BitFieldArrayConstIterator<position, bits, size, T, S>;
+
+public:
+  constexpr T Value() const { return m_array->Value(m_index); };
+  constexpr operator T() const { return Value(); }
+
+private:
+  constexpr BitFieldArrayConstRef(const BitFieldArray<position, bits, size, T, S>* array,
+                                  size_t index)
+      : m_array(array), m_index(index)
+  {
+  }
+
+  const BitFieldArray<position, bits, size, T, S>* const m_array;
+  const size_t m_index;
+};
+
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+class BitFieldArrayRef
+{
+  friend struct BitFieldArray<position, bits, size, T, S>;
+  friend class BitFieldArrayIterator<position, bits, size, T, S>;
+
+public:
+  constexpr T Value() const { return m_array->Value(m_index); };
+  constexpr operator T() const { return Value(); }
+  T operator=(const BitFieldArrayRef<position, bits, size, T, S>& value) const
+  {
+    m_array->SetValue(m_index, value);
+    return value;
+  }
+  T operator=(T value) const
+  {
+    m_array->SetValue(m_index, value);
+    return value;
+  }
+
+private:
+  constexpr BitFieldArrayRef(BitFieldArray<position, bits, size, T, S>* array, size_t index)
+      : m_array(array), m_index(index)
+  {
+  }
+
+  BitFieldArray<position, bits, size, T, S>* const m_array;
+  const size_t m_index;
+};
+
+// Satisfies LegacyOutputIterator / std::output_iterator.
+// Does not satisfy LegacyInputIterator / std::input_iterator as std::output_iterator_tag does not
+// extend std::input_iterator_tag.
+// Does not satisfy LegacyForwardIterator / std::forward_iterator, as that requires use of real
+// references instead of proxy objects.
+// This iterator allows use of BitFieldArray in range-based for loops, and with fmt::join.
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+class BitFieldArrayIterator
+{
+  friend struct BitFieldArray<position, bits, size, T, S>;
+
+public:
+  using iterator_category = std::output_iterator_tag;
+  using value_type = T;
+  using difference_type = ptrdiff_t;
+  using pointer = void;
+  using reference = BitFieldArrayRef<position, bits, size, T, S>;
+
+private:
+  constexpr BitFieldArrayIterator(BitFieldArray<position, bits, size, T, S>* array, size_t index)
+      : m_array(array), m_index(index)
+  {
+  }
+
+public:
+  // Required by std::input_or_output_iterator
+  constexpr BitFieldArrayIterator() = default;
+  // Required by LegacyIterator
+  constexpr BitFieldArrayIterator(const BitFieldArrayIterator& other) = default;
+  // Required by LegacyIterator
+  BitFieldArrayIterator& operator=(const BitFieldArrayIterator& other) = default;
+  // Move constructor and assignment operators, explicitly defined for completeness
+  constexpr BitFieldArrayIterator(BitFieldArrayIterator&& other) = default;
+  BitFieldArrayIterator& operator=(BitFieldArrayIterator&& other) = default;
+
+public:
+  BitFieldArrayIterator& operator++()
+  {
+    m_index++;
+    return *this;
+  }
+  BitFieldArrayIterator operator++(int)
+  {
+    BitFieldArrayIterator other(*this);
+    ++*this;
+    return other;
+  }
+  constexpr reference operator*() const { return reference(m_array, m_index); }
+  constexpr bool operator==(BitFieldArrayIterator other) const { return m_index == other.m_index; }
+  constexpr bool operator!=(BitFieldArrayIterator other) const { return m_index != other.m_index; }
+
+private:
+  BitFieldArray<position, bits, size, T, S>* m_array;
+  size_t m_index;
+};
+
+// Satisfies LegacyInputIterator / std::input_iterator.
+// Does not satisfy LegacyForwardIterator / std::forward_iterator, as that requires use of real
+// references instead of proxy objects.
+// This iterator allows use of BitFieldArray in range-based for loops, and with fmt::join.
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+class BitFieldArrayConstIterator
+{
+  friend struct BitFieldArray<position, bits, size, T, S>;
+
+public:
+  using iterator_category = std::input_iterator_tag;
+  using value_type = T;
+  using difference_type = ptrdiff_t;
+  using pointer = void;
+  using reference = BitFieldArrayConstRef<position, bits, size, T, S>;
+
+private:
+  constexpr BitFieldArrayConstIterator(const BitFieldArray<position, bits, size, T, S>* array,
+                                       size_t index)
+      : m_array(array), m_index(index)
+  {
+  }
+
+public:
+  // Required by std::input_or_output_iterator
+  constexpr BitFieldArrayConstIterator() = default;
+  // Required by LegacyIterator
+  constexpr BitFieldArrayConstIterator(const BitFieldArrayConstIterator& other) = default;
+  // Required by LegacyIterator
+  BitFieldArrayConstIterator& operator=(const BitFieldArrayConstIterator& other) = default;
+  // Move constructor and assignment operators, explicitly defined for completeness
+  constexpr BitFieldArrayConstIterator(BitFieldArrayConstIterator&& other) = default;
+  BitFieldArrayConstIterator& operator=(BitFieldArrayConstIterator&& other) = default;
+
+public:
+  BitFieldArrayConstIterator& operator++()
+  {
+    m_index++;
+    return *this;
+  }
+  BitFieldArrayConstIterator operator++(int)
+  {
+    BitFieldArrayConstIterator other(*this);
+    ++*this;
+    return other;
+  }
+  constexpr reference operator*() const { return reference(m_array, m_index); }
+  constexpr bool operator==(BitFieldArrayConstIterator other) const
+  {
+    return m_index == other.m_index;
+  }
+  constexpr bool operator!=(BitFieldArrayConstIterator other) const
+  {
+    return m_index != other.m_index;
+  }
+
+private:
+  const BitFieldArray<position, bits, size, T, S>* m_array;
+  size_t m_index;
+};
+
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+struct fmt::formatter<BitFieldArrayRef<position, bits, size, T, S>>
+{
+  fmt::formatter<T> m_formatter;
+  constexpr auto parse(format_parse_context& ctx) { return m_formatter.parse(ctx); }
+  template <typename FormatContext>
+  auto format(const BitFieldArrayRef<position, bits, size, T, S>& ref, FormatContext& ctx)
+  {
+    return m_formatter.format(ref.Value(), ctx);
+  }
+};
+
+template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
+struct fmt::formatter<BitFieldArrayConstRef<position, bits, size, T, S>>
+{
+  fmt::formatter<T> m_formatter;
+  constexpr auto parse(format_parse_context& ctx) { return m_formatter.parse(ctx); }
+  template <typename FormatContext>
+  auto format(const BitFieldArrayConstRef<position, bits, size, T, S>& ref, FormatContext& ctx)
+  {
+    return m_formatter.format(ref.Value(), ctx);
+  }
+};