int8 version of NUMERIC?

In Interbase and Firebird, NUMERIC is implemented as 64-bit integer.
This limits the range to NUMERIC(18, *) but for many uses that's
adequate. And moreover it's fast and efficient.

Is there a way in PostgreSQL to do something similar, i.e. I want to:

- use 64-bit ints, not string bits or arbitrary precision which is
dubbed as "much slower than ints" in the documentation;

- use decimals, like NUMERIC(18,4);

- store and retrieve decimal numbers pretty much transparently (e.g. I
don't want to remember to insert 123456 for 12.3456 and playing with
multiplying/dividing by 10000);

--
dave