Bug 1312104 - part 1 - use BitwiseCast for punning between uint64_t/double in indexedDB; r=janv

We have code elsewhere for this sort of stuff; let's use it here.

dom/indexedDB/ActorsParent.cpp

@@ -21,6 +21,7 @@
 #include "mozilla/Attributes.h"
 #include "mozilla/AppProcessChecker.h"
 #include "mozilla/AutoRestore.h"
+#include "mozilla/Casting.h"
 #include "mozilla/EndianUtils.h"
 #include "mozilla/LazyIdleThread.h"
 #include "mozilla/Maybe.h"
@@ -18960,12 +18961,7 @@ uint64_t
 DatabaseOperationBase::ReinterpretDoubleAsUInt64(double aDouble)
 {
   // This is a duplicate of the js engine's byte munging in StructuredClone.cpp
-  union {
-    double d;
-    uint64_t u;
-  } pun;
-  pun.d = aDouble;
-  return pun.u;
+  return BitwiseCast<uint64_t>(aDouble);
 }
 
 // static

dom/indexedDB/Key.cpp

@@ -12,6 +12,7 @@
 #include "js/Date.h"
 #include "js/Value.h"
 #include "jsfriendapi.h"
+#include "mozilla/Casting.h"
 #include "mozilla/EndianUtils.h"
 #include "mozilla/FloatingPoint.h"
 #include "mozIStorageStatement.h"
@@ -594,11 +595,6 @@ Key::DecodeString(const unsigned char*& aPos, const unsigned char* aEnd,
   aPos = iter + 1;
 }
 
-union Float64Union {
-  double d;
-  uint64_t u;
-}; 
-
 void
 Key::EncodeNumber(double aFloat, uint8_t aType)
 {
@@ -612,13 +608,12 @@ Key::EncodeNumber(double aFloat, uint8_t aType)
 
   *(buffer++) = aType;
 
-  Float64Union pun;
-  pun.d = aFloat;
+  uint64_t bits = BitwiseCast<uint64_t>(aFloat);
   // Note: The subtraction from 0 below is necessary to fix
   // MSVC build warning C4146 (negating an unsigned value).
-  uint64_t number = pun.u & PR_UINT64(0x8000000000000000) ?
-                    (0 - pun.u) :
-                    (pun.u | PR_UINT64(0x8000000000000000));
+  uint64_t number = bits & PR_UINT64(0x8000000000000000) ?
+                    (0 - bits) :
+                    (bits | PR_UINT64(0x8000000000000000));
 
   mozilla::BigEndian::writeUint64(buffer, number);
 }
@@ -638,14 +633,13 @@ Key::DecodeNumber(const unsigned char*& aPos, const unsigned char* aEnd)
 
   aPos += sizeof(number);
 
-  Float64Union pun;
   // Note: The subtraction from 0 below is necessary to fix
   // MSVC build warning C4146 (negating an unsigned value).
-  pun.u = number & PR_UINT64(0x8000000000000000) ?
-          (number & ~PR_UINT64(0x8000000000000000)) :
-          (0 - number);
+  uint64_t bits = number & PR_UINT64(0x8000000000000000) ?
+                  (number & ~PR_UINT64(0x8000000000000000)) :
+                  (0 - number);
 
-  return pun.d;
+  return BitwiseCast<double>(bits);
 }
 
 void