croncpp returning time in the past near the DST

[enrico-samknows]

Hi, I've found a strange case which fails:

#include "include/croncpp.h"
#include <iostream>

int main() {

   try {

     setenv("TZ", "CET-1CEST,M3.5.0,M10.5.0/3", 1);
     tzset();

     auto cron_string = std::string{ "30 55 5,11,17 * * *" };
     auto cron = cron::make_cron(cron_string);

     std::time_t now = 1679777644;
     std::time_t next = cron::cron_next(cron, now);

     std::cout << "Now:  " << now << std::endl;
     std::cout << "Next: " << next << std::endl;

  }
  catch (cron::bad_cronexpr const & ex)
  {
    std::cerr << ex.what() << '\n';
  }

}

prints:

Now:  1679777644
Next: 1679720130

where next < now.
Am I doing something wrong with the invocation here?
Thanks!

[enrico-samknows]

FYI this doesn't happen if I always set date.tm_isdst = -1; before returning in add_to_field, set_field and reset_field. That's good enough for my usage but I think it has performance implications, so I'm not opening a PR.