is_ascii Oracle function

Here is an Oracle function that tells whether a column is all ASCII (from Mark Stafford):

create or replace function is_ascii (v varchar2) return varchar2 as
 r boolean := false;
begin
 r := length(v)
   - length(
       translate(v
         , chr(1)
           || translate(v, chr(1) || ' !"#$%&''()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~', chr(1) )
         , chr(1)
       )
   ) = 0;
 if v is null then r := true; end if;
 if r = true then return 'y'; else return 'n'; end if;
exception
 when others then
   return null;
end;
/