NTP rollover-safe design with ESP8266 (Curiosity)
This implementation is perfectly fine. The calculations are done with
unsigned numbers, so they are naturally rollover safe. The day NTP time
rolls over, secsSince1900 will become a very small number, and
subtracting SEVENZYYEARS from it will cause an extra roll over. Owing
to the rules of modular arithmetics, these two rollovers compensate and
you are guaranteed to get the correct result modulo
232&nbsp;s.

In the end, you get a Unix time as an unsigned 32-bit integer. Unix time
is traditionally signed, which makes the 32-bit representation roll over
in January&nbsp;2038. The authors of this library have instead chosen to
represent it as an unsigned number, which means it will roll over in
February&nbsp;2106.