On Wed, Aug 12, 2015 at 5:34 PM, nusenu nusenu@openmailbox.org wrote:
from today's measurement meeting:
15:00:20 <virgil> karsten: I've decided I'm going to fix the definition of median 15:00:26 <virgil> in the tor sourcecode 15:00:36 <karsten> virgil: is it broken? 15:00:53 <karsten> or just not specified as clearly as it should be? 15:01:01 <virgil> for ordered list {a,b,c,d}, it returns b instead of (b+c)/2. 15:01:24 <karsten> yes. maybe that's for a reason (which I don't know). 15:01:40 <virgil> I look forward to hearing this reason when my patch is rejected. 15:01:41 <karsten> like, using value (b+c)/2 would break for some reason, whereas any of a, b, c, d would be fine. 15:01:45 <Sebastian> you cannot do that 15:01:51 <Sebastian> without breaking Tor's voting 15:02:21 <Sebastian> Tor's specification requires low median for a bunch of directory stuff
I'd be interested in the reason as well.
The correct fix here is to update the code documentation to define the functions as returning the low-median, and to update dir-spec.txt to say so too. I'd accept documentation patches like that.
Changing the code to return the mean of the two center elements from even arrays would break all authority voting, and wouldn't actually be useful.