static EncodedJSValue setNewValueFromDateArgs(ExecState* exec, int numArgsToUse, bool inputIsUTC)
{
    JSValue thisValue = exec->thisValue();
    if (!thisValue.inherits(DateInstance::info()))
        return throwVMTypeError(exec);

    DateInstance* thisDateObj = asDateInstance(thisValue);
    if (!exec->argumentCount()) {
        JSValue result = jsNaN();
        thisDateObj->setInternalValue(exec->vm(), result);
        return JSValue::encode(result);
    }

    VM& vm = exec->vm();
    double milli = thisDateObj->internalNumber();
    double ms = 0; 

    GregorianDateTime gregorianDateTime; 
    if (numArgsToUse == 3 && std::isnan(milli)) 
        msToGregorianDateTime(vm, 0, true, gregorianDateTime);
    else { 
        ms = milli - floor(milli / msPerSecond) * msPerSecond; 
        const GregorianDateTime* other = inputIsUTC 
            ? thisDateObj->gregorianDateTimeUTC(exec)
            : thisDateObj->gregorianDateTime(exec);
        if (!other)
            return JSValue::encode(jsNaN());
        gregorianDateTime.copyFrom(*other);
    }
    
    if (!fillStructuresUsingDateArgs(exec, numArgsToUse, &ms, &gregorianDateTime)) {
        JSValue result = jsNaN();
        thisDateObj->setInternalValue(vm, result);
        return JSValue::encode(result);
    } 
           
    JSValue result = jsNumber(gregorianDateTimeToMS(vm, gregorianDateTime, ms, inputIsUTC));
    thisDateObj->setInternalValue(vm, result);
    return JSValue::encode(result);
}
static JSValue setNewValueFromDateArgs(ExecState* exec, JSValue thisValue, const ArgList& args, int numArgsToUse, bool inputIsUTC)
{
    if (!thisValue.isObject(&DateInstance::info))
        return throwError(exec, TypeError);

    DateInstance* thisDateObj = asDateInstance(thisValue);
    if (args.isEmpty()) {
        JSValue result = jsNaN(exec);
        thisDateObj->setInternalValue(result);
        return result;
    }      
    
    double milli = thisDateObj->internalNumber();
    double ms = 0;

    GregorianDateTime t;
    if (numArgsToUse == 3 && isnan(milli))
        // Based on ECMA 262 15.9.5.40 - .41 (set[UTC]FullYear)
        // the time must be reset to +0 if it is NaN. 
        thisDateObj->msToGregorianDateTime(0, true, t);
    else {
        double secs = floor(milli / msPerSecond);
        ms = milli - secs * msPerSecond;
        thisDateObj->msToGregorianDateTime(milli, inputIsUTC, t);
    }
    
    if (!fillStructuresUsingDateArgs(exec, args, numArgsToUse, &ms, &t)) {
        JSValue result = jsNaN(exec);
        thisDateObj->setInternalValue(result);
        return result;
    } 
           
    JSValue result = jsNumber(exec, gregorianDateTimeToMS(t, ms, inputIsUTC));
    thisDateObj->setInternalValue(result);
    return result;
}