LibJS: Store Date milliseconds as signed to support negative offsets

We need to support the range of -999 to 999.

Userland/Libraries/LibJS/Runtime/Date.cpp

@@ -14,7 +14,7 @@
 
 namespace JS {
 
-Date* Date::create(GlobalObject& global_object, Core::DateTime datetime, u16 milliseconds, bool is_invalid)
+Date* Date::create(GlobalObject& global_object, Core::DateTime datetime, i16 milliseconds, bool is_invalid)
 {
     return global_object.heap().allocate<Date>(global_object, datetime, milliseconds, is_invalid, *global_object.date_prototype());
 }
@@ -24,11 +24,11 @@ Date* Date::now(GlobalObject& global_object)
     struct timeval tv;
     gettimeofday(&tv, nullptr);
     auto datetime = Core::DateTime::now();
-    auto milliseconds = static_cast<u16>(tv.tv_usec / 1000);
+    auto milliseconds = static_cast<i16>(tv.tv_usec / 1000);
     return create(global_object, datetime, milliseconds);
 }
 
-Date::Date(Core::DateTime datetime, u16 milliseconds, bool is_invalid, Object& prototype)
+Date::Date(Core::DateTime datetime, i16 milliseconds, bool is_invalid, Object& prototype)
     : Object(prototype)
     , m_datetime(datetime)
     , m_milliseconds(milliseconds)

Userland/Libraries/LibJS/Runtime/Date.h

@@ -15,10 +15,10 @@ class Date final : public Object {
     JS_OBJECT(Date, Object);
 
 public:
-    static Date* create(GlobalObject&, Core::DateTime, u16 milliseconds, bool is_invalid = false);
+    static Date* create(GlobalObject&, Core::DateTime, i16 milliseconds, bool is_invalid = false);
     static Date* now(GlobalObject&);
 
-    Date(Core::DateTime datetime, u16 milliseconds, bool is_invalid, Object& prototype);
+    Date(Core::DateTime datetime, i16 milliseconds, bool is_invalid, Object& prototype);
     virtual ~Date() override;
 
     Core::DateTime& datetime() { return m_datetime; }
@@ -27,7 +27,7 @@ public:
     int date() const { return datetime().day(); }
     int day() const { return datetime().weekday(); }
     int hours() const { return datetime().hour(); }
-    u16 milliseconds() const { return m_milliseconds; }
+    i16 milliseconds() const { return m_milliseconds; }
     int minutes() const { return datetime().minute(); }
     int month() const { return datetime().month() - 1; }
     int seconds() const { return datetime().second(); }
@@ -46,7 +46,7 @@ public:
     int utc_month() const;
     int utc_seconds() const;
 
-    void set_milliseconds(u16 milliseconds)
+    void set_milliseconds(i16 milliseconds)
     {
         m_milliseconds = milliseconds;
     }
@@ -79,7 +79,7 @@ private:
     tm to_utc_tm() const;
 
     Core::DateTime m_datetime;
-    u16 m_milliseconds;
+    i16 m_milliseconds;
     bool m_is_invalid { false };
 };
 

Userland/Libraries/LibJS/Runtime/DateConstructor.cpp

@@ -152,7 +152,7 @@ Value DateConstructor::construct(Function&)
 
     auto create_invalid_date = [this]() {
         auto datetime = Core::DateTime::create(1970, 1, 1, 0, 0, 0);
-        auto milliseconds = static_cast<u16>(0);
+        auto milliseconds = static_cast<i16>(0);
         return Date::create(global_object(), datetime, milliseconds, true);
     };
 
@@ -173,7 +173,7 @@ Value DateConstructor::construct(Function&)
         // A timestamp since the epoch, in UTC.
         double value_as_double = value.as_double();
         auto datetime = Core::DateTime::from_timestamp(static_cast<time_t>(value_as_double / 1000));
-        auto milliseconds = static_cast<u16>(fmod(value_as_double, 1000));
+        auto milliseconds = static_cast<i16>(fmod(value_as_double, 1000));
         return Date::create(global_object(), datetime, milliseconds);
     }