96  * some recent year avoids lots of unnecessary loop iterations in conversion.
113  *   ( ((year % 4) == 0 &&
114  *      (year % 100) != 0) ||
115  *     ((year % 400) == 0) )
119 leapyear(int year)  in leapyear()  argument
123 	if ((year & 3) == 0) {  in leapyear()
125 		if ((year % 100) == 0) {  in leapyear()
127 			if ((year % 400) == 0)  in leapyear()
137 	int i, year, days;  in clock_ct_to_ts()  local
146 	 * Many realtime clocks store the year as 2-digit BCD; pivot on 70 to  in clock_ct_to_ts()
148 	 * year += 100, so interpret values between 70-199 as relative to 1900.  in clock_ct_to_ts()
150 	year = ct->year;  in clock_ct_to_ts()
151 	if (year < 70)  in clock_ct_to_ts()
152 		year += 2000;  in clock_ct_to_ts()
153 	else if (year < 200)  in clock_ct_to_ts()
154 		year += 1900;  in clock_ct_to_ts()
158 	    ct->day > days_in_month(year, ct->mon) ||  in clock_ct_to_ts()
159 	    ct->hour > 23 ||  ct->min > 59 || ct->sec > 59 || year < 1970 ||  in clock_ct_to_ts()
160 	    (sizeof(time_t) == 4 && year > 2037)) {	/* time_t overflow */  in clock_ct_to_ts()
170 	if (year >= recent_base_year) {  in clock_ct_to_ts()
177 	for (; i < year; i++)  in clock_ct_to_ts()
182 	  	days += days_in_month(year, i);  in clock_ct_to_ts()
201 	 * Year may come in as 2-digit or 4-digit BCD.  Split the value into  in clock_bcd_to_ts()
202 	 * separate BCD century and year values for validation and conversion.  in clock_bcd_to_ts()
204 	bcent = bct->year >> 8;  in clock_bcd_to_ts()
205 	byear = bct->year & 0xff;  in clock_bcd_to_ts()
218 			    bct->year, bct->mon, bct->day,  in clock_bcd_to_ts()
223 	ct.year = FROMBCD(byear) + FROMBCD(bcent) * 100;  in clock_bcd_to_ts()
246 	time_t i, year, days;  in clock_ts_to_ct()  local
258 		year = recent_base_year;  in clock_ts_to_ct()
261 		year = POSIX_BASE_YEAR;  in clock_ts_to_ct()
263 	for (; days >= days_in_year(year); year++)  in clock_ts_to_ct()
264 		days -= days_in_year(year);  in clock_ts_to_ct()
265 	ct->year = year;  in clock_ts_to_ct()
268 	for (i = 1; days >= days_in_month(year, i); i++)  in clock_ts_to_ct()
269 		days -= days_in_month(year, i);  in clock_ts_to_ct()
289 	KASSERT(ct->year >= 0 && ct->year < 10000,  in clock_ts_to_ct()
290 	    ("year %d isn't a 4 digit year", ct->year));  in clock_ts_to_ct()
322 	bct->year = TOBCD(ct.year % 100) | (TOBCD(ct.year / 100) << 8);  in clock_ts_to_bcd()
340 		    bct->year, bct->mon, bct->day,  in clock_print_bcd()
345 		    bct->year, bct->mon, bct->day,  in clock_print_bcd()
358 		    ct->year, ct->mon, ct->day,  in clock_print_ct()
363 		    ct->year, ct->mon, ct->day,  in clock_print_ct()