From: | Rikard Bosnjakovic <rikard(dot)bosnjakovic(at)gmail(dot)com> |
---|---|
To: | Nathaniel Trellice <naptrel(at)yahoo(dot)co(dot)uk> |
Cc: | pgsql-novice(at)postgresql(dot)org |
Subject: | Re: Bit count |
Date: | 2009-11-24 18:18:00 |
Message-ID: | d9e88eaf0911241018p7b95bdaaqc65717bb6b663a60@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-novice |
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
From | Date | Subject | |
---|---|---|---|
Next Message | Kenneth Marshall | 2009-11-24 18:23:02 | Re: Bit count |
Previous Message | Richard Broersma | 2009-11-24 17:31:03 | Re: PostgreSQL 8.4.1 and pljava |