Bit count

To record unique visitors per day, I'll flip the bit corresponding to a user's id.

Each event type will have a separate record.
It is possible to get useful information using union(&) and intersection(|) of several fields.

Is there a built-in function to count bits similar to BIT_COUNT in mysql and BITCOUNT in redis?

I've found several plpgsql functions in the mailing list.

What is the best function to use for large bitstrings (>100KB)?

Thanks

CREATE OR REPLACE FUNCTION bitcount(i integer) RETURNS integer AS $$
DECLARE n integer;
DECLARE amount integer;
  BEGIN
    amount := 0;
    FOR n IN 1..16 LOOP
      amount := amount + ((i >> (n-1)) & 1);
    END LOOP;
    RETURN amount;
  END
$$ LANGUAGE plpgsql;

create or replace function bitsetlen(bit) returns int as $$
declare i int;
        c int;
begin
    c:=0;
    for i in 1..length($1) loop
        if substring($1,i,1)=B'1' then
            c:=c+1;
        end if;
    end loop;
    return c;
end;
$$ language plpgsql;


SELECT (myBit & 1 + myBit >> 1 & 1 + myBit >> 2 & 1) AS bitCount FROM myBitTable;

SELECT LENGTH( REPLACE( CAST( B'101000000000000000000010' AS TEXT ), '0', ''));