如何将一个Float值转换为actionscript中的日期

I am using as3xlsx reader to read the excel data and if it is date format,i am getting a floating point value like 41520.2916666667 which is actually 03-Sep-2013, in that case I need to convert the float value to date object in flex/as3. Is there any method to convert float to date in as3? I tried time stamp to date but it is not correct.I am using as3xlsx reader to read the excel dat