Postgres GIN on fixed length bit string

Question

I'm try to create GIN for fast similarity search on bitsrings on postgres 9.6.

I use tanimoto/jaccard similarity metric:

tanimoto = popcount(bs1 & bs2)/popcount(bs1 | bs2)

where 0 - is totally not similar and 1 - is identical.

update:

popcount - is count of true bits. bs1, bs2 - bitstrings.

I use query like this:

SELECT bs, tanimoto(B'11100000', bs) as t FROM test WHERE bs % B'11100000'

on table:

 CREATE TABLE test (bs bit(8));

% operator is bool(tanimoto(bs, B'11100000') > treshold)

treshold configurable.

How can I enable GIN or how to implement operator_class if need?

I want to implement this http://pubs.acs.org/doi/abs/10.1021/ci200552r index