localtime.c

   1 #include <sys/time.h>
   2 #include <sys/types.h>
   3 #include <time.h>
   4
   5 #define isleap(y)       (!((y) % 4) && ((y) % 100) || !((y) % 400))
   6 #define SPD             (24 * 60 * 60)
   7
   8 long timezone;
   9
  10 void tzset(void)
  11 {
  12         struct timezone tz;
  13         gettimeofday(0, &tz);
  14         timezone = tz.tz_minuteswest * 60;
  15 }
  16
  17 static void tp2tm(struct tm *tm, time_t t)
  18 {
  19         static int dpm[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  20         long days = t / SPD;
  21         long rem = t % SPD;
  22         int i;
  23         tm->tm_sec = rem % 60;
  24         rem /= 60;
  25         tm->tm_min = rem % 60;
  26         tm->tm_hour = rem / 60;
  27         tm->tm_wday = (4 + days) % 7;
  28
  29         /* calculating yday and year */
  30         for (i = 1970; days >= 365 + isleap(i); i++)
  31                 days -= 365 + isleap(i);
  32         tm->tm_year = i - 1900;
  33         tm->tm_yday = days;
  34
  35         /* calculating mday and mon */
  36         tm->tm_mday = 1;
  37         if (isleap(i) && days == 59)
  38                 tm->tm_mday++;
  39         if (isleap(i) && days >= 59)
  40                 days--;
  41         for (i = 0; i < 11 && days >= dpm[i]; i++)
  42                 days -= dpm[i];
  43         tm->tm_mon = i;
  44         tm->tm_mday += days;
  45 }
  46
  47 struct tm *localtime(long *t)
  48 {
  49         static struct tm tm;
  50         tzset();
  51         tp2tm(&tm, *t - timezone);
  52         return &tm;
  53 }
  54
  55 struct tm *gmtime(long *t)
  56 {
  57         static struct tm tm;
  58         tp2tm(&tm, *t);
  59         return &tm;
  60 }