Hijri date

[ViViD]

Hello ,
Our country in middle east has a different offical date than christian date . There is a php function for conversion of this dates to eachother . But I don't know where is the best place to add this function . We were add this function to functions.php but after version 3 , the admincp gets the date from functions.php and when I edit a user , the all dates changes to 1970 after saving because of an invalid date of functions.php delieverd.

Please guide me where is the best place to have an addintional date field or conversion of current field ... I am not proffesional in php but have some playing with it .

Thanks for your help