Make BitField and ResultCode constexpr-initializable

src/common/bit_field.h

@@ -108,7 +108,7 @@
  * symptoms.
  */
 #pragma pack(1)
-template <std::size_t position, std::size_t bits, typename T>
+template <std::size_t Position, std::size_t Bits, typename T>
 struct BitField {
 private:
     // We hide the copy assigment operator here, because the default copy
@@ -117,40 +117,6 @@ private:
     // We don't delete it because we want BitField to be trivially copyable.
     BitField& operator=(const BitField&) = default;
 
-public:
-    // This constructor and assignment operator might be considered ambiguous:
-    // Would they initialize the storage or just the bitfield?
-    // Hence, delete them. Use the Assign method to set bitfield values!
-    BitField(T val) = delete;
-    BitField& operator=(T val) = delete;
-
-    // Force default constructor to be created
-    // so that we can use this within unions
-    BitField() = default;
-
-    FORCE_INLINE operator T() const {
-        return Value();
-    }
-
-    FORCE_INLINE void Assign(const T& value) {
-        storage = (storage & ~GetMask()) | (((StorageType)value << position) & GetMask());
-    }
-
-    FORCE_INLINE T Value() const {
-        if (std::numeric_limits<T>::is_signed) {
-            std::size_t shift = 8 * sizeof(T) - bits;
-            return (T)((storage << (shift - position)) >> shift);
-        } else {
-            return (T)((storage & GetMask()) >> position);
-        }
-    }
-
-    // TODO: we may want to change this to explicit operator bool() if it's bug-free in VS2015
-    FORCE_INLINE bool ToBool() const {
-        return Value() != 0;
-    }
-
-private:
     // 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
@@ -161,10 +127,63 @@ private:
     // Unsigned version of StorageType
     typedef typename std::make_unsigned<StorageType>::type StorageTypeU;
 
-    FORCE_INLINE StorageType GetMask() const {
-        return (((StorageTypeU)~0) >> (8 * sizeof(T) - bits)) << position;
+public:
+    /// Constants to allow limited introspection of fields if needed
+    static constexpr size_t position = Position;
+    static constexpr size_t bits = Bits;
+    static constexpr StorageType mask = (((StorageTypeU)~0) >> (8 * sizeof(T) - bits)) << position;
+
+    /**
+     * Formats a value by masking and shifting it according to the field parameters. A value
+     * containing several bitfields can be assembled by formatting each of their values and ORing
+     * the results together.
+     */
+    static constexpr FORCE_INLINE StorageType FormatValue(const T& value) {
+        return ((StorageType)value << position) & mask;
     }
 
+    /**
+     * Extracts a value from the passed storage. In most situations prefer use the member functions
+     * (such as Value() or operator T), but this can be used to extract a value from a bitfield
+     * union in a constexpr context.
+     */
+    static constexpr FORCE_INLINE T ExtractValue(const StorageType& storage) {
+        if (std::numeric_limits<T>::is_signed) {
+            std::size_t shift = 8 * sizeof(T) - bits;
+            return (T)((storage << (shift - position)) >> shift);
+        } else {
+            return (T)((storage & mask) >> position);
+        }
+    }
+
+    // This constructor and assignment operator might be considered ambiguous:
+    // Would they initialize the storage or just the bitfield?
+    // Hence, delete them. Use the Assign method to set bitfield values!
+    BitField(T val) = delete;
+    BitField& operator=(T val) = delete;
+
+    // Force default constructor to be created
+    // so that we can use this within unions
+    constexpr BitField() = default;
+
+    FORCE_INLINE operator T() const {
+        return Value();
+    }
+
+    FORCE_INLINE void Assign(const T& value) {
+        storage = (storage & ~mask) | FormatValue(value);
+    }
+
+    FORCE_INLINE T Value() const {
+        return ExtractValue(storage);
+    }
+
+    // TODO: we may want to change this to explicit operator bool() if it's bug-free in VS2015
+    FORCE_INLINE bool ToBool() const {
+        return Value() != 0;
+    }
+
+private:
     StorageType storage;
 
     static_assert(bits + position <= 8 * sizeof(T), "Bitfield out of range");

src/core/hle/result.h

@@ -228,45 +228,42 @@ union ResultCode {
     // error
     BitField<31, 1, u32> is_error;
 
-    explicit ResultCode(u32 raw) : raw(raw) {}
-    ResultCode(ErrorDescription description_, ErrorModule module_, ErrorSummary summary_,
-               ErrorLevel level_)
-        : raw(0) {
-        description.Assign(description_);
-        module.Assign(module_);
-        summary.Assign(summary_);
-        level.Assign(level_);
-    }
+    constexpr explicit ResultCode(u32 raw) : raw(raw) {}
 
-    ResultCode& operator=(const ResultCode& o) {
+    constexpr ResultCode(ErrorDescription description_, ErrorModule module_, ErrorSummary summary_,
+                         ErrorLevel level_)
+        : raw(description.FormatValue(description_) | module.FormatValue(module_) |
+              summary.FormatValue(summary_) | level.FormatValue(level_)) {}
+
+    constexpr ResultCode& operator=(const ResultCode& o) {
         raw = o.raw;
         return *this;
     }
 
-    bool IsSuccess() const {
-        return is_error == 0;
+    constexpr bool IsSuccess() const {
+        return is_error.ExtractValue(raw) == 0;
     }
 
-    bool IsError() const {
-        return is_error == 1;
+    constexpr bool IsError() const {
+        return is_error.ExtractValue(raw) == 1;
     }
 };
 
-inline bool operator==(const ResultCode& a, const ResultCode& b) {
+constexpr bool operator==(const ResultCode& a, const ResultCode& b) {
     return a.raw == b.raw;
 }
 
-inline bool operator!=(const ResultCode& a, const ResultCode& b) {
+constexpr bool operator!=(const ResultCode& a, const ResultCode& b) {
     return a.raw != b.raw;
 }
 
 // Convenience functions for creating some common kinds of errors:
 
 /// The default success `ResultCode`.
-const ResultCode RESULT_SUCCESS(0);
+constexpr ResultCode RESULT_SUCCESS(0);
 
 /// Might be returned instead of a dummy success for unimplemented APIs.
-inline ResultCode UnimplementedFunction(ErrorModule module) {
+constexpr ResultCode UnimplementedFunction(ErrorModule module) {
     return ResultCode(ErrorDescription::NotImplemented, module, ErrorSummary::NotSupported,
                       ErrorLevel::Permanent);
 }