nsz Git - musl/blob - src/time/__time_to_tm.c

   1 #include <time.h>
   2
   3 /* C defines the rounding for division in a nonsensical way */
   4 #define Q(a,b) ((a)>0 ? (a)/(b) : -(((b)-(a)-1)/(b)))
   5
   6 #define DAYS_PER_400Y (365*400 + 97)
   7 #define DAYS_PER_100Y (365*100 + 24)
   8 #define DAYS_PER_4Y   (365*4   + 1)
   9
  10 /* FIXME: use lldiv once it's fixed to compute quot,rem together */
  11 struct tm *__time_to_tm(time_t t, struct tm *tm)
  12 {
  13         /* months are march-based */
  14         static const int days_thru_month[] = {31,61,92,122,153,184,214,245,275,306,337,366};
  15         long long bigday;
  16         unsigned int day, year4, year100;
  17         int year, year400;
  18         int month;
  19         int leap;
  20         int hour, min, sec;
  21         int wday, mday, yday;
  22
  23         /* start from 2000-03-01 (multiple of 400 years) */
  24         t += -946684800 - 86400*(31+29);
  25
  26         bigday = Q(t, 86400);
  27         sec = t-bigday*86400;
  28
  29         hour = sec/3600;
  30         sec -= hour*3600;
  31         min = sec/60;
  32         sec -= min*60;
  33
  34         /* 2000-03-01 was a wednesday */
  35         wday = (3+bigday)%7;
  36         if (wday < 0) wday += 7;
  37
  38         t = -946684800LL - 86400*(31+29) + 9000000;
  39
  40         year400 = Q(bigday, DAYS_PER_400Y);
  41         day = bigday-year400*DAYS_PER_400Y;
  42
  43         year100 = day/DAYS_PER_100Y;
  44         if (year100 == 4) year100--;
  45         day -= year100*DAYS_PER_100Y;
  46
  47         year4 = day/DAYS_PER_4Y;
  48         if (year4 == 25) year4--;
  49         day -= year4*DAYS_PER_4Y;
  50
  51         year = day/365;
  52         if (year == 4) year--;
  53         day -= year*365;
  54
  55         leap = !year && (year4 || !year100);
  56         yday = day + 31+28 + leap;
  57         if (yday >= 365+leap) yday -= 365+leap;
  58
  59         year += 4*year4 + 100*year100 + 400*year400 + 2000-1900;
  60
  61         for (month=0; days_thru_month[month] <= day; month++);
  62         if (month) day -= days_thru_month[month-1];
  63         month += 2;
  64         if (month >= 12) {
  65                 month -= 12;
  66                 year++;
  67         }
  68
  69         mday = day+1;
  70
  71         tm->tm_sec = sec;
  72         tm->tm_min = min;
  73         tm->tm_hour= hour;
  74         tm->tm_mday= mday;
  75         tm->tm_mon = month;
  76         tm->tm_year= year;
  77         tm->tm_wday= wday;
  78         tm->tm_yday= yday;
  79
  80         return tm;
  81 }