[tz] [PROPOSED] Fix ambiguous leapsecs by rolling up to a minute

[Paul Eggert]

On 9/13/21 11:41 AM, John Sauter wrote:
> his means that conversion between UTC and local time is always
> possible and is reversible.  The down side is that the GMT offset is
> not constant, but that is only true for a few seconds near the leap
> second.

That's another way to interpret the situation, yes. However, an 
advantage of the proposed patch's approach is that the UTC offset 
(tm_gmtoff) remains constant, thus satisfying the civil-time rules that 
Michael mentioned.

The only difference between the proposed patch, and what you're 
suggesting, is that in the proposed patch when calculating the UTC 
offset a minute's seconds on or after an inserted leap second are all 
counted relative to the next minute, not relative to the previous one.