Plpgsql function to compute "every other Friday"

Hey folks,

So, I'm working on a little application to help me with my
budget. Yeah, there are apps out there to do it, but I'm having
a good time learning some more too. :)

I get paid every other Friday. I thought, for scheduling
purposes in this app, that I would take a stab at writing a plpgsql
function to determine if a given date is a payday. Here is what I
have so far:

CREATE OR REPLACE FUNCTION is_payday( d DATE ) RETURNS BOOLEAN AS $$

DECLARE epoch DATE;
days_since_epoch INTEGER;
mult FLOAT8;
ret BOOLEAN := FALSE;

BEGIN

SELECT INTO epoch option_value
FROM options WHERE option_name = 'payroll_epoch';

SELECT INTO days_since_epoch ( SELECT CURRENT_DATE - d);

*** here's where I'm stuck ***

RETURN ret;

END;
$$ LANGUAGE plpgsql;

OK. So, I have a "starting" payday (payroll_epoch) in an options
table. That is the first payday of the year. I then calculate the
number of days between that value and the date I pass to the function.
Now I need to calculate whether this delta (how many days since
epoch) is an even multiple of 14 days (the two weeks).

I have no idea how to do that in plpgsql. Basically, I need to
figure out if the date I pass to the function is a payday, and if
it is, return TRUE.

I would very much appreciate any help with this last bit of math
and syntax, as well as any advice on whether this is a reasonable
way to attack the problem. And no - this isn't a homework
assignment. :)

Thanks folks!

Benny

--
"Hairy ape nads." -- Colleen, playing Neverwinter Nights