[LEAPSECS] BBC radio Crowd Science

[Warner Losh]

On Tue, Jan 31, 2017 at 8:24 PM, Zefram <zefram at fysh.org> wrote:
> Warner Losh wrote:
>>changes at the start of the positive leap second, or at the start of
>>the first second after a negative label has been removed. Otherwise
>>the irregular radix math doesn't work out.
>
> The maths isn't done in the irregular radix.

What standard says that?

>  For the purposes of
> expressions such as "TAI - UTC" that require a UTC time to be reduced to
> a scalar value, that scalar is derived using the regular radix values.
> This means that, yes, 2016-12-31T23:59:60 and 2017-01-01T00:00:00 have the
> same scalar value.  The jump of TAI-UTC up by 1 s causes the repetition
> of the preceding 1 s worth of UTC scalar values.

Only for time_t computations. That's a very interesting conversation,
but that's a different conversation. TF.460 says nothing about this.
It only defines how seconds are labeled around a leap second. UTC has
a list of second labels. These second labels are an irregular radix,
and if you want to mechanically convert the TAI second labels to the
UTC second labels, you have to play that insane game, or a game that
maps onto it. "reducing to a scalar value" unfortunately doesn't map
1-1 onto UTC. Since it isn't 1-1, onto, it can't be standards
conforming which defines a 1-1 / onto mapping both ways between TAI
and UTC.

Warner