Re: Bit count

On Tue, Nov 24, 2009 at 16:47, Nathaniel Trellice <naptrel(at)yahoo(dot)co(dot)uk> wrote:

[...]
> If not, can anyone recommend the most efficient way within postgres to implement the kind of bit-counting tricks found at:

Perhaps something like this:

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;

bos=# select bitcount(6);
bitcount
----------
2
(1 row)

bos=# select bitcount(7);
bitcount
----------
3

bos=# select bitcount(4711);
bitcount
----------
7
(1 row)

bos=# select bitcount(1024);
bitcount
----------
1
(1 row)

--
- Rikard