I am using below method to generate a hash in oracle:

select STANDARD_HASH(x, 'SHA1'), length(STANDARD_HASH(x, 'SHA1')) from (
    select 'aa' x from dual union all
    select 'bb' x from dual union all
    select 'cc' x from dual
)

As you can see it always generates a RAW data with length as 40.

I need a hash of length RAW(8) instead of RAW(40). Is there any readily available way to do it?
If no, is there a way to generate a hash of length RAW(8) using DBMS_CRYPTO?