[LEAPSECS] stale leap second information

[Tim Shepard]

>    +-------+-----------+-----+---------------------+---------------+
>    |1 1 1 1|M M M M M M M M M|L L L L L L L L L|D D|C C C C C C C C|
>    +-------+-----------+-----+---------------------+---------------+
>     3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 
>     1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
> 
> The first four bits are constant 0xf putting the resulting IPv4 in
> the "Class-E" segment which is reserved.  This should give us 100%
> certainty in detecting meddling DNS resolvers.
> 
> The "M" field is nine bit unsigned month number:
> 
> 	(year - 1972) * 12 + month - 1
> 
> The "L" field the eight bit signed(!) TAI-UTC difference before the
> start of the indicated month.
> 


I think you meant to make your M field be ten bits wide.  At
nine bits wide it will have already wrapped around a few
months ago, but your python code doesn't handle this field
wrapping around.  At 10 bits wide it will wrap around in the
year 2057 if the back of my envelope is correct.

And your L field says eight bits wide but your diagram shows
it as 9 bits wide.

And there's some inconsistency in your ascii art for the box
that just adds to the confusion.


			-Tim Shepard
			 shep at alum.mit.edu