Bug 1940819: Implement ParamTraits<std::bitset<N>>. r=ipc-reviewers,nika

Differential Revision: https://phabricator.services.mozilla.com/D233754

ipc/glue/IPCMessageUtilsSpecializations.h

@@ -495,14 +495,21 @@ struct ParamTraits<mozilla::EnumSet<T, U>> {
     return false;
   }
 
+  static constexpr size_t kUnderlyingWidth = [] {
+    if constexpr (std::numeric_limits<serializedType>::is_specialized) {
+      return std::numeric_limits<serializedType>::digits;
+    } else {
+      return serializedType().size();  // for std::bitset<N>
+    }
+  }();
+
   static constexpr serializedType AllEnumBits() {
-    return ~serializedType(0) >> (std::numeric_limits<serializedType>::digits -
-                                  (mozilla::MaxEnumValue<T>::value + 1));
+    return ~serializedType(0) >>
+           (kUnderlyingWidth - (mozilla::MaxEnumValue<T>::value + 1));
   }
 
   static constexpr bool IsLegalValue(const serializedType value) {
-    static_assert(mozilla::MaxEnumValue<T>::value <
-                      std::numeric_limits<serializedType>::digits,
+    static_assert(mozilla::MaxEnumValue<T>::value < kUnderlyingWidth,
                   "Enum max value is not in the range!");
     static_assert(
         std::is_unsigned<decltype(mozilla::MaxEnumValue<T>::value)>::value,
@@ -847,6 +854,29 @@ struct ParamTraits<gfxPlatform::GlobalReflowFlags>
                                     gfxPlatform::GlobalReflowFlags::ALL_BITS> {
 };
 
+template <size_t N>
+struct ParamTraits<std::bitset<N>> {
+  typedef std::bitset<N> paramType;
+  static void Write(MessageWriter* aWriter, const paramType& aParam) {
+    paramType mask(UINT64_MAX);
+    for (size_t i = 0; i < N; i += 64) {
+      uint64_t value = ((aParam >> i) & mask).to_ullong();
+      WriteParam(aWriter, value);
+    }
+  }
+
+  static bool Read(MessageReader* aReader, paramType* aResult) {
+    for (size_t i = 0; i < N; i += 64) {
+      uint64_t value = 0;
+      if (!ReadParam(aReader, &value)) {
+        return false;
+      }
+      *aResult |= std::bitset<N>(value) << i;
+    }
+    return true;
+  }
+};
+
 } /* namespace IPC */
 
 #endif /* __IPC_GLUE_IPCMESSAGEUTILSSPECIALIZATIONS_H__ */