[tz] NetBSD vs Darwin timezone API

[Paul Eggert]

On 11/10/2016 05:12 PM, Guy Harris wrote:
>> Emacs wants a consistent and complete snapshot of the current rule set for all times from now into the indefinite future.
> To what use does it put that snapshot?

It's the calendar code contributed by E.M. Reingold. As I recall, Emacs 
can tell you what day and time DST is scheduled to begin in the year 
2039, even on a platform with signed 32-bit time_t so that 
localtime/mktime do not work that far into the future. The calendar code 
uses Y-M-D arithmetic to work around the Y2038 problem. (Lots of hairy 
stuff there, written back when you couldn't reasonably tell people to 
get 64-bit machines but people still wanted to calculate the date of 
Easter 1066 in the Julian calendar, that sort of thing.)