Zeller's Algorithm

[Paul A Storm <paul.a.storm@lmco.com>]

Help!

I am trying to find a Ada implementation of Zeller's algorithm that
works!  I have found several on the web
but none of them have worked right.

For example I tried this one from
http://www.adapower.com/alg/zeller.html  Inputting June 19 2002 returns
Wednesday, correct.  Inputting June 19 1999 produces Sunday, incorrect. 
That's a Saturday. Inputting
February 3, 2002 produces Friday, incorrect.  That's a Sunday.  What
gives?

I have had similar weird results using other similar Ada Zeller versions
I've found on the web.

I'm wondering if maybe there's a difference in rounding down.  Perhaps a
83 vs. 95 peculiarity?
I don't think so.  It produces compilation errors using the -gnat83
switch.

I'm running gnat 3.13a on Sun 2.6

Argh!  Anybody got any ideas on how to fix this or know of an Ada
implementation of Zeller's algorithm
that works?

Paul Storm