Integer division and remainder

[Robert Amesz]

Mark Jackson wrote:

> Robert Amesz <reqhye72zux at mailexpire.com> writes:
>
>> [Zeller's congruence and the mod-function]
>>
>> On Python the problem wouldn't have occurred, its mod-function is
>> mathematically correct.  
> 
> Yes!  That was the very problem with the old to-do list
> manager xvtdl, which I fixed back in early 2000; find the code at
> http://www.alumni.caltech.edu/~mjackson/xvtdl.html.  While
> diagnosing this behavior I implemented the algorithm in Python for
> test purposes, and was led astray for a while by the fact that it
> *didn't* fail!

I personally call that "Murphy's Law of Debugging": just as you need  
things to go wrong, they will go inexplicably right. [*]

 
> Q:  What multiple of 7 did I add to the critical expression in the
>     Zeller algorithm so it will remain nonnegative for the next few 
>     centuries? 
> 
> A:  42

LOL, yes, that should do the trick. And Douglas Adams recently died at 
the age of 49, the next multiple of 7...


Robert Amesz
-- 
[*] Which is really just 'straight' Murphy except that in this case 
right is wrong and wrong is right. If that sounds like the witches from 
MacBeth, well, sometimes debugging is a lot like black magic.