Factor out bit_cast.

2 files changed, 43 insertions, 14 deletions

diff --git a/src/support/utilities.h b/src/support/utilities.h
new file mode 100644
index 000000000..77263a78e
--- /dev/null
+++ b/src/support/utilities.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2016 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 wasm_support_utilities_h
+#define wasm_support_utilities_h
+
+#include <cstring>
+#include <type_traits>
+
+namespace wasm {
+
+// Type punning needs to be done through this function to avoid undefined
+// behavior: unions and reinterpret_cast aren't valid approaches.
+template <class Destination, class Source>
+inline Destination bit_cast(const Source& source) {
+  static_assert(sizeof(Destination) == sizeof(Source),
+                "bit_cast needs to be between types of the same size");
+  static_assert(std::is_pod<Destination>::value, "non-POD bit_cast undefined");
+  static_assert(std::is_pod<Source>::value, "non-POD bit_cast undefined");
+  Destination destination;
+  std::memcpy(&destination, &source, sizeof(destination));
+  return destination;
+}
+
+}  // namespace wasm
+
+#endif   // wasm_support_utilities_h
diff --git a/src/wasm.h b/src/wasm.h
index 8cba16e8c..97e0bfc12 100644
--- a/src/wasm.h
+++ b/src/wasm.h
@@ -58,6 +58,7 @@
 #include "emscripten-optimizer/simple_ast.h"
 #include "mixed_arena.h"
 #include "pretty_printing.h"
+#include "support/utilities.h"
 
 namespace wasm {
 
@@ -190,15 +191,9 @@ struct Literal {
 
   static void printFloat(std::ostream &o, float f) {
     if (isnan(f)) {
-      union {
-        float ff;
-        uint32_t ll;
-      } fu, iu;
-      fu.ff = f;
-      memcpy(&iu, &fu, sizeof(fu));
       const char *sign = std::signbit(f) ? "-" : "";
       o << sign << "nan";
-      if (uint32_t payload = ~0xffc00000u & iu.ll) {
+      if (uint32_t payload = ~0xffc00000u & bit_cast<uint32_t>(f)) {
         o << ":0x" << std::hex << payload << std::dec;
       }
       return;
@@ -212,15 +207,9 @@ struct Literal {
       return;
     }
     if (isnan(d)) {
-      union {
-        double dd;
-        uint64_t ll;
-      } du, iu;
-      du.dd = d;
-      memcpy(&iu, &du, sizeof(du));
       const char *sign = std::signbit(d) ? "-" : "";
       o << sign << "nan";
-      if (uint64_t payload = ~0xfff8000000000000ull & iu.ll) {
+      if (uint64_t payload = ~0xfff8000000000000ull & bit_cast<uint64_t>(d)) {
         o << ":0x" << std::hex << payload << std::dec;
       }
       return;