Force signed zero double.

src/conversions.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 35 matching lines @@
 
 
 inline bool isDigit(int x, int radix) {
   return (x >= '0' && x <= '9' && x < '0' + radix)
       || (radix > 10 && x >= 'a' && x < 'a' + radix - 10)
       || (radix > 10 && x >= 'A' && x < 'A' + radix - 10);
 }
 
 
 inline double SignedZero(bool negative) {
-  return negative ? -0.0 : 0.0;
+  return negative ? BitCast<double, uint64_t>(Double::kSignMask) : 0.0;
 }
 
 
 // The fast double-to-(unsigned-)int conversion routine does not guarantee
 // rounding towards zero.
 // For NaN and values outside the int range, return INT_MIN or INT_MAX.
 inline int FastD2IChecked(double x) {
   if (!(x >= INT_MIN)) return INT_MIN;  // Negation to catch NaNs.
   if (x > INT_MAX) return INT_MAX;
   return static_cast<int>(x);
@@ skipping 80 matching lines @@
 // Additional number to string conversions for the number type.
 // The caller is responsible for calling free on the returned pointer.
 char* DoubleToFixedCString(double value, int f);
 char* DoubleToExponentialCString(double value, int f);
 char* DoubleToPrecisionCString(double value, int f);
 char* DoubleToRadixCString(double value, int radix);
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONVERSIONS_H_