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diff --git a/third_party/wasm2c/src/cast.h b/third_party/wasm2c/src/cast.h
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+++ b/third_party/wasm2c/src/cast.h
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+/*
+ * Copyright 2017 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef WABT_CAST_H_
+#define WABT_CAST_H_
+
+#include <memory>
+#include <type_traits>
+
+#include "src/common.h"
+
+// Modeled after LLVM's dynamic casts:
+// http://llvm.org/docs/ProgrammersManual.html#the-isa-cast-and-dyn-cast-templates
+//
+// Use isa<T>(foo) to check whether foo is a T*:
+//
+//     if (isa<Minivan>(car)) {
+//        ...
+//     }
+//
+// Use cast<T>(foo) when you know that foo is a T* -- it will assert that the
+// type matches:
+//
+//     switch (car.type) {
+//       case CarType::Minivan: {
+//         auto minivan = cast<Minivan>(car);
+//         ...
+//       }
+//     }
+//
+// Use dyn_cast<T>(foo) as a combination if isa and cast, it will return
+// nullptr if the type doesn't match:
+//
+//     if (auto minivan = dyn_cast<Minivan>(car)) {
+//       ...
+//     }
+//
+//
+// To use these classes in a type hierarchy, you must implement classof:
+//
+//     enum CarType { Minivan, ... };
+//     struct Car { CarType type; ... };
+//     struct Minivan : Car {
+//       static bool classof(const Car* car) { return car->type == Minivan; }
+//       ...
+//     };
+//
+
+namespace wabt {
+
+template <typename Derived, typename Base>
+bool isa(const Base* base) {
+  WABT_STATIC_ASSERT((std::is_base_of<Base, Derived>::value));
+  return Derived::classof(base);
+}
+
+template <typename Derived, typename Base>
+const Derived* cast(const Base* base) {
+  assert(isa<Derived>(base));
+  return static_cast<const Derived*>(base);
+};
+
+template <typename Derived, typename Base>
+Derived* cast(Base* base) {
+  assert(isa<Derived>(base));
+  return static_cast<Derived*>(base);
+};
+
+template <typename Derived, typename Base>
+const Derived* dyn_cast(const Base* base) {
+  return isa<Derived>(base) ? static_cast<const Derived*>(base) : nullptr;
+};
+
+template <typename Derived, typename Base>
+Derived* dyn_cast(Base* base) {
+  return isa<Derived>(base) ? static_cast<Derived*>(base) : nullptr;
+};
+
+// Cast functionality for unique_ptr. isa and dyn_cast are not included because
+// they won't always pass ownership back to the caller.
+
+template <typename Derived, typename Base>
+std::unique_ptr<const Derived> cast(std::unique_ptr<const Base>&& base) {
+  assert(isa<Derived>(base.get()));
+  return std::unique_ptr<Derived>(static_cast<const Derived*>(base.release()));
+};
+
+template <typename Derived, typename Base>
+std::unique_ptr<Derived> cast(std::unique_ptr<Base>&& base) {
+  assert(isa<Derived>(base.get()));
+  return std::unique_ptr<Derived>(static_cast<Derived*>(base.release()));
+};
+
+}  // namespace wabt
+
+#endif  // WABT_CAST_H_