Calculating a New Date

I've got a program that calculates a new date based upon a number of days 
offset.  Here is a snippet of the code:

. . . 
C     *entry        Plist                                         
C                   Parm                    indate                
C                   Parm                    dateformat        5   
C                   Parm                    diffdays          4 0 
C                   Parm                    outdate               
C*                                                                
C                   Select                                        
C*                                                                
C     dateformat    WhenEq    '*MDY'                              
C     dateformat    OrEq      '*mdy'                              
C     *mdy          Move      inmdy         @date                 
C                   AddDur    diffdays:*days@xxxx                 
C     *mdy          Move      @date         outmdy        
. . .

I'm enhancing the logic to handle all valid date formats, to allow the option 
specification of an output date format, and will be prototyping the parameters.

Does anyone have a sample of a program like this already written?  I'm going to 
end up overhauling this thing and would like to save a lot of time if it's 
already been done.  BTW, I'm at V5R2 and am not against free form code.

Bill