Implementing product-aggregate

Hi,

we need a product aggregate and used to implement this as

exp(sum(ln([COLUMN])))

While using the sum of logarithms is working RDBMS-independently, we'd like to
switch to a more PostgreSQL native way of doing this and implement an
aggregate to be used. Currently the implementation is

create aggregate prod(numeric) (sfunc = numeric_mul, stype = numeric)

This is simply calling the implementation funtion of the *-Operator for the numeric
datatype. Since I could not find any documentation of this implementation
function, I am wondering, if using a possibly internal function might be a bad idea.

Are there any recommendations on this?

Thanks for any input!

--
MfG Jan