[LEAPSECS] POSIX and C (Was: Re: ISO Influence)

[Ian Batten]

On 22 Dec 2010, at 20:36, Steve Allen wrote:


> On Wed 2010-12-22T18:46:56 +0000, Poul-Henning Kamp hath writ:

>> Broadcast time *IS* civil time, it is broadcast as a service to  

>> civilians.

>>

>> Take Germanys DCF77 as example:

>>

>> DCF77 is the official legal time of Germany[1].

>

> By transmitting timestamps which are not UTC DCF77 is not in

> conformance with ITU-R TF.460.


The ITU's writ does not extend to specifying what the German  
government does within Germany to broadcast German civil time to  
German civilians.

The same applies, mutatis mutandis, to the UK.  MSF broadcasts legal  
UK time, summer time corrected when it in force.  So an application  
which takes the BCD time from MSF and displays it, unmediated, is  
certain to always be broadcasting UK legal time.  That's what it's  
there for.  There is a bit (58B, I think) which indicates that summer  
time is in force, so if you know what the base time zone for the UK  
is, you can recover UTC all year around by subtracting one hour when  
appropriate.

But if the UK moved to UTC+1/+2, which isn't at all impossible, an  
application that assumed that MSF was broadcasting UTC or UTC+1  
(switched by the summer time bit) would lose big.  Unless there was a  
fundamental change to the purpose of MSF, it would switch to  
broadcasting UTC+1 in the winter, UTC+2 in the summer, with bit 58B  
(or whatever) indicating which was which; there would not, however, be  
any indication that the base timezone was now UTC+1.

Unlike (it would appear) DCF77, MSF does supply DUT1.  But the format  
(unary encoded) is such that it cannot deal with |DUT1|>0.9 without  
changing the format.

ian