[LEAPSECS] Negative TAI-UTC

[Warner Losh]

On Tue, Feb 7, 2017 at 12:03 PM, Zefram <zefram at fysh.org> wrote:
> Clive D.W. Feather wrote:
>>probability is that TAI-UTC will ever be negative? Should data structures
>>be designed to handle this case or not bother?
>
> Data structures should certainly allow for the possibility, but in
> space-constrained cases can be optimised based on the understanding that
> it's relatively unlikely.  If a fixed-size field is being designed,
> then the range of TAI-UTC values that it can accommodate can be made
> asymmetric, favouring positive values.  An 8-bit field might reasonably be
> made to use excess-32 encoding, encompassing values [-32, 223], giving it
> a good chance of covering the next century's evolution of Earth rotation.
> (8 bits is minimal for that design objective; I'd press for more bits
> if possible.)  A variable-length encoding can in principle cover all
> possible values, but could still benefit by making the representations
> of negative numbers longer than the representations of positive numbers.

So long as after the number is decoded, it's decoded into an signed
number. This is a clever way to get a fuller range of likely leaps
without precluding rare, but possible events.

Warner