Hi,
 
I think what you're looking at here is the Mystery mansion program that was
in the CSL and floating around years ago.  The EXEC routine that is being
called
is used to transfer between code segments, and was (if I remember correctly)
in an RL segment, and written in SPL.
 
I sure someone on this list can help you find the rest of the source if it's
no longer in the CSL (you'll have to contact whoever has rights to the code
in order to use it).  I think the program was originally for the HP1000 and
the EXEC routine was written to facilitate porting to the HP3000.
 
The code is definitely FORTRAN66, and you can find the functions (other than
those specially coded in the RL ) in the FORTRAN/3000 reference manual, and
perhaps in the COMPILER LIBRARY and/or SCIENTIFIC LIBRARY reference manuals,
both of which would be for a classic HP3000 of the late 1970s vintage.
 
Hope this helps a bit,
 
Jeff Flowers