Daylight saving time calculation

is_daylight_saving_time_in_poland.c

// is PoLish Daylight Saving Time - source: https://en.wikipedia.org/wiki/Daylight_saving_time_by_country
// month - Month (1..12)
// date  - Day of the month (1..31)
// dow   - Day Of Week (1..7)
uint8_t isPLDST(uint8_t month, uint8_t date, uint8_t dow) {
  if (month < 3 || month > 10) return 0;
  if (month > 3 && month < 10) return 1;
  uint8_t prevSunday = date > dow ? date - dow : 0;
  if (month == 3) return prevSunday >= 25;
  else  // month == 10
    return prevSunday < 25;
}