diff options
Diffstat (limited to 'src/lib/rtc.c')
| -rw-r--r-- | src/lib/rtc.c | 60 |
1 files changed, 22 insertions, 38 deletions
diff --git a/src/lib/rtc.c b/src/lib/rtc.c index c5c157f8bd..3e4c3f77c3 100644 --- a/src/lib/rtc.c +++ b/src/lib/rtc.c @@ -27,57 +27,41 @@ #define DAYS_IN_YEAR(a) (LEAP_YEAR(a) ? 366 : 365) #define DAYS_IN_MONTH(a) (month_days[(a) - 1]) -static const int month_offset[] = { - 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 -}; - static const char *const weekdays[] = { - "Sun", "Mon", "Tues", "Wednes", "Thurs", "Fri", "Satur", + "Sun", "Mon", "Tues", "Wednes", "Thurs", "Fri", "Satur" }; -static int leaps_to_year(int year) -{ - return year / 4 - year / 100 + year / 400; -} - -/* This only works for the Gregorian calendar after Jan 1 1971. */ +/* Zeller's rule */ static int rtc_calc_weekday(struct rtc_time *tm) { - int leaps_to_date; - int day; - if (tm->year < 1971) return -1; - day = 4; /* Jan 1 1970 was a Thursday. */ - - /* Number of leap corrections to apply up to end of last year */ - leaps_to_date = leaps_to_year(tm->year - 1) - leaps_to_year(1970); + /* In Zeller's rule, January and February are treated as if they + are months 13 and 14 of the previous year (March is still month 3) */ + const int zyear = ((tm->mon < 3) ? tm->year - 1 : tm->year); + const int q = tm->mday; + const int m = (tm->mon < 3) ? tm->mon + 12 : tm->mon; + const int K = zyear % 100; + const int J = zyear / 100; /* - * This year is a leap year if it is divisible by 4 except when it is - * divisible by 100 unless it is divisible by 400 - * - * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 is. + * Because of the way the modulo operator works with negative numbers, + * the traditional formulation of Zeller's rule must be modified + * slightly to make the numerator positive (i.e., add 5J instead of + * subtracting 2J). Also subtract 1 so that Sunday is day 0. */ - if ((tm->year % 4) && - ((tm->year % 100 != 0) || (tm->year % 400 == 0)) && - (tm->mon > 2)) { - /* We are past Feb. 29 in a leap year */ - day++; - } - - day += (tm->year - 1970) * 365 + leaps_to_date + - month_offset[tm->mon-1] + tm->mday; - tm->wday = day % 7; + const int h = (q + (13 * (m + 1)) / 5 + + K + (K / 4) + (J / 4) + (5 * J) - 1) % 7; + tm->wday = h; return 0; } int rtc_to_tm(int tim, struct rtc_time *tm) { int month_days[12] = { - 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 + 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }; register int i; register long hms, day; @@ -112,7 +96,7 @@ int rtc_to_tm(int tim, struct rtc_time *tm) /* * Converts Gregorian date to seconds since 1970-01-01 00:00:00. - * Assumes input in normal date format, i.e. 1980-12-31 23:59:59 + * Assumes input in normal date format, i.e. 1980-12-31 23:59:59 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59. * * [For the Julian calendar (which was used in Russia before 1917, @@ -130,7 +114,7 @@ unsigned long rtc_mktime(const struct rtc_time *tm) { int mon = tm->mon; int year = tm->year; - int days, hours; + int days, hours; mon -= 2; if (0 >= (int)mon) { /* 1..12 -> 11, 12, 1..10 */ @@ -139,15 +123,15 @@ unsigned long rtc_mktime(const struct rtc_time *tm) } days = (unsigned long)(year / 4 - year / 100 + year / 400 + - 367 * mon / 12 + tm->mday) + - year * 365 - 719499; + 367 * mon / 12 + tm->mday) + + year * 365 - 719499; hours = days * 24 + tm->hour; return (hours * 60 + tm->min) * 60 + tm->sec; } void rtc_display(const struct rtc_time *tm) { - printk(BIOS_INFO, "Date: %4d-%02d-%02d (%sday) Time: %2d:%02d:%02d\n", + printk(BIOS_INFO, "Date: %5d-%02d-%02d (%sday) Time: %2d:%02d:%02d\n", tm->year, tm->mon, tm->mday, (tm->wday < 0 || tm->wday > 6) ? "unknown " : weekdays[tm->wday], tm->hour, tm->min, tm->sec); |