Access double fields in C++ as uint64_t fields to preserve signaling bit of a NaN.

src/objects.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 #include <memory>
 
@@ skipping 1818 matching lines @@
 
 
 // The HeapNumber class describes heap allocated numbers that cannot be
 // represented in a Smi (small integer)
 class HeapNumber: public HeapObject {
  public:
   // [value]: number value.
   inline double value() const;
   inline void set_value(double value);
 
+  inline uint64_t value_as_bits() const;
+  inline void set_value_as_bits(uint64_t bits);
+
   DECLARE_CAST(HeapNumber)
 
   // Dispatched behavior.
   bool HeapNumberBooleanValue();
 
   V8_EXPORT_PRIVATE void HeapNumberPrint(std::ostream& os);  // NOLINT
   DECLARE_VERIFIER(HeapNumber)
 
   inline int get_exponent();
   inline int get_sign();
@@ skipping 652 matching lines @@
                                 int unused_property_fields, const char* reason);
 
   inline bool IsUnboxedDoubleField(FieldIndex index);
 
   // Access fast-case object properties at index.
   static Handle<Object> FastPropertyAt(Handle<JSObject> object,
                                        Representation representation,
                                        FieldIndex index);
   inline Object* RawFastPropertyAt(FieldIndex index);
   inline double RawFastDoublePropertyAt(FieldIndex index);
+  inline uint64_t RawFastDoublePropertyAsBitsAt(FieldIndex index);
 
   inline void FastPropertyAtPut(FieldIndex index, Object* value);
   inline void RawFastPropertyAtPut(FieldIndex index, Object* value);
-  inline void RawFastDoublePropertyAtPut(FieldIndex index, double value);
+  inline void RawFastDoublePropertyAsBitsAtPut(FieldIndex index, uint64_t bits);
   inline void WriteToField(int descriptor, PropertyDetails details,
                            Object* value);
 
   // Access to in object properties.
   inline int GetInObjectPropertyOffset(int index);
   inline Object* InObjectPropertyAt(int index);
   inline Object* InObjectPropertyAtPut(int index,
                                        Object* value,
                                        WriteBarrierMode mode
                                        = UPDATE_WRITE_BARRIER);
@@ skipping 9188 matching lines @@
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #include "src/objects/object-macros-undef.h"
 
 #endif  // V8_OBJECTS_H_