> DLLIMPORT int addfunc( int a, int b )
> {
> return a + b;
> }
>
> testdll.sql
>
> DECLARE EXTERNAL FUNCTION addfunc
> INTEGER, INTEGER
> RETURNS INTEGER
> ENTRY_POINT 'addfunc' MODULE_NAME 'testdll';

Input parameters are always passed as pointers to values.
Output value is also passed using pointer,
unless you specify RETURNS INTEGER BY VALUE
(can be used only for simple types, not Timestamp, Varchar, ...)

Ivan
http://www.volny.cz/iprenosil/interbase/