newlib/libc/time/tzcalc_limits.c

   1 /*
   2  * tzcalc_limits.c
   3  * Original Author: Adapted from tzcode maintained by Arthur David Olson.
   4  * Modifications:
   5  * - Changed to mktm_r and added __tzcalc_limits - 04/10/02, Jeff Johnston
   6  * - Fixed bug in mday computations - 08/12/04, Alex Mogilnikov <alx@intellectronika.ru>
   7  * - Fixed bug in __tzcalc_limits - 08/12/04, Alex Mogilnikov <alx@intellectronika.ru>
   8  * - Moved __tzcalc_limits() to separate file - 05/09/14, Freddie Chopin <freddie_chopin@op.pl>
   9  */
  10
  11 #include "local.h"
  12
  13 int
  14 __tzcalc_limits (int year)
  15 {
  16   int days, year_days, years;
  17   int i, j;
  18   __tzinfo_type *const tz = __gettzinfo ();
  19
  20   if (year < EPOCH_YEAR)
  21     return 0;
  22
  23   tz->__tzyear = year;
  24
  25   years = (year - EPOCH_YEAR);
  26
  27   year_days = years * 365 +
  28     (years - 1 + EPOCH_YEARS_SINCE_LEAP) / 4 -
  29     (years - 1 + EPOCH_YEARS_SINCE_CENTURY) / 100 +
  30     (years - 1 + EPOCH_YEARS_SINCE_LEAP_CENTURY) / 400;
  31
  32   for (i = 0; i < 2; ++i)
  33     {
  34       if (tz->__tzrule[i].ch == 'J')
  35         {
  36           /* The Julian day n (1 <= n <= 365). */
  37           days = year_days + tz->__tzrule[i].d +
  38             (isleap(year) && tz->__tzrule[i].d >= 60);
  39           /* Convert to yday */
  40           --days;
  41         }
  42       else if (tz->__tzrule[i].ch == 'D')
  43         days = year_days + tz->__tzrule[i].d;
  44       else
  45         {
  46           const int yleap = isleap(year);
  47           int m_day, m_wday, wday_diff;
  48           const int *const ip = __month_lengths[yleap];
  49
  50           days = year_days;
  51
  52           for (j = 1; j < tz->__tzrule[i].m; ++j)
  53             days += ip[j-1];
  54
  55           m_wday = (EPOCH_WDAY + days) % DAYSPERWEEK;
  56
  57           wday_diff = tz->__tzrule[i].d - m_wday;
  58           if (wday_diff < 0)
  59             wday_diff += DAYSPERWEEK;
  60           m_day = (tz->__tzrule[i].n - 1) * DAYSPERWEEK + wday_diff;
  61
  62           while (m_day >= ip[j-1])
  63             m_day -= DAYSPERWEEK;
  64
  65           days += m_day;
  66         }
  67
  68       /* store the change-over time in GMT form by adding offset */
  69       tz->__tzrule[i].change = (time_t) days * SECSPERDAY +
  70       tz->__tzrule[i].s + tz->__tzrule[i].offset;
  71     }
  72
  73   tz->__tznorth = (tz->__tzrule[0].change < tz->__tzrule[1].change);
  74
  75   return 1;
  76 }