drivers/rtc/date.c

   1 /*
   2  * (C) Copyright 2001
   3  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
   4  *
   5  * SPDX-License-Identifier:     GPL-2.0+
   6  */
   7
   8 #include <common.h>
   9 #include <command.h>
  10 #include <errno.h>
  11 #include <rtc.h>
  12
  13 #if defined(CONFIG_CMD_DATE) || defined(CONFIG_TIMESTAMP)
  14
  15 #define FEBRUARY                2
  16 #define STARTOFTIME             1970
  17 #define SECDAY                  86400L
  18 #define SECYR                   (SECDAY * 365)
  19 #define leapyear(year)          ((year) % 4 == 0)
  20 #define days_in_year(a)         (leapyear(a) ? 366 : 365)
  21 #define days_in_month(a)        (month_days[(a) - 1])
  22
  23 static int month_days[12] = {
  24         31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
  25 };
  26
  27 static int month_offset[] = {
  28         0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
  29 };
  30
  31 /*
  32  * This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
  33  */
  34 int rtc_calc_weekday(struct rtc_time *tm)
  35 {
  36         int leaps_to_date;
  37         int last_year;
  38         int day;
  39
  40         if (tm->tm_year < 1753)
  41                 return -1;
  42         last_year = tm->tm_year - 1;
  43
  44         /* Number of leap corrections to apply up to end of last year */
  45         leaps_to_date = last_year / 4 - last_year / 100 + last_year / 400;
  46
  47         /*
  48          * This year is a leap year if it is divisible by 4 except when it is
  49          * divisible by 100 unless it is divisible by 400
  50          *
  51          * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 is.
  52          */
  53         if (tm->tm_year % 4 == 0 &&
  54             ((tm->tm_year % 100 != 0) || (tm->tm_year % 400 == 0)) &&
  55             tm->tm_mon > 2) {
  56                 /* We are past Feb. 29 in a leap year */
  57                 day = 1;
  58         } else {
  59                 day = 0;
  60         }
  61
  62         day += last_year * 365 + leaps_to_date + month_offset[tm->tm_mon - 1] +
  63                         tm->tm_mday;
  64         tm->tm_wday = day % 7;
  65
  66         return 0;
  67 }
  68
  69 int rtc_to_tm(int tim, struct rtc_time *tm)
  70 {
  71         register int i;
  72         register long hms, day;
  73
  74         day = tim / SECDAY;
  75         hms = tim % SECDAY;
  76
  77         /* Hours, minutes, seconds are easy */
  78         tm->tm_hour = hms / 3600;
  79         tm->tm_min = (hms % 3600) / 60;
  80         tm->tm_sec = (hms % 3600) % 60;
  81
  82         /* Number of years in days */
  83         for (i = STARTOFTIME; day >= days_in_year(i); i++)
  84                 day -= days_in_year(i);
  85         tm->tm_year = i;
  86
  87         /* Number of months in days left */
  88         if (leapyear(tm->tm_year))
  89                 days_in_month(FEBRUARY) = 29;
  90         for (i = 1; day >= days_in_month(i); i++)
  91                 day -= days_in_month(i);
  92         days_in_month(FEBRUARY) = 28;
  93         tm->tm_mon = i;
  94
  95         /* Days are what is left over (+1) from all that */
  96         tm->tm_mday = day + 1;
  97
  98         /* Zero unused fields */
  99         tm->tm_yday = 0;
 100         tm->tm_isdst = 0;
 101
 102         /*
 103          * Determine the day of week
 104          */
 105         return rtc_calc_weekday(tm);
 106 }
 107
 108 /*
 109  * Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 110  * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 111  * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 112  *
 113  * [For the Julian calendar (which was used in Russia before 1917,
 114  * Britain & colonies before 1752, anywhere else before 1582,
 115  * and is still in use by some communities) leave out the
 116  * -year / 100 + year / 400 terms, and add 10.]
 117  *
 118  * This algorithm was first published by Gauss (I think).
 119  *
 120  * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 121  * machines where long is 32-bit! (However, as time_t is signed, we
 122  * will already get problems at other places on 2038-01-19 03:14:08)
 123  */
 124 unsigned long rtc_mktime(const struct rtc_time *tm)
 125 {
 126         int mon = tm->tm_mon;
 127         int year = tm->tm_year;
 128         int days, hours;
 129
 130         mon -= 2;
 131         if (0 >= (int)mon) {    /* 1..12 -> 11, 12, 1..10 */
 132                 mon += 12;      /* Puts Feb last since it has leap day */
 133                 year -= 1;
 134         }
 135
 136         days = (unsigned long)(year / 4 - year / 100 + year / 400 +
 137                         367 * mon / 12 + tm->tm_mday) +
 138                         year * 365 - 719499;
 139         hours = days * 24 + tm->tm_hour;
 140         return (hours * 60 + tm->tm_min) * 60 + tm->tm_sec;
 141 }
 142
 143 #endif