newlib/libc/time/gmtime_r.c

   1 /*
   2  * gmtime_r.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  * - Move code from _mktm_r() to gmtime_r() - 05/09/14, Freddie Chopin <freddie_chopin@op.pl>
   9  * - Fixed bug in calculations for dates after year 2069 or before year 1901. Ideas for
  10  *   solution taken from musl's __secs_to_tm() - 07/12/2014, Freddie Chopin
  11  *   <freddie_chopin@op.pl>
  12  * - Use faster algorithm from civil_from_days() by Howard Hinnant - 12/06/2014,
  13  * Freddie Chopin <freddie_chopin@op.pl>
  14  *
  15  * Converts the calendar time pointed to by tim_p into a broken-down time
  16  * expressed as local time. Returns a pointer to a structure containing the
  17  * broken-down time.
  18  */
  19
  20 #include "local.h"
  21
  22 /* Move epoch from 01.01.1970 to 01.03.0000 (yes, Year 0) - this is the first
  23  * day of a 400-year long "era", right after additional day of leap year.
  24  * This adjustment is required only for date calculation, so instead of
  25  * modifying time_t value (which would require 64-bit operations to work
  26  * correctly) it's enough to adjust the calculated number of days since epoch.
  27  */
  28 #define EPOCH_ADJUSTMENT_DAYS   719468L
  29 /* year to which the adjustment was made */
  30 #define ADJUSTED_EPOCH_YEAR     0
  31 /* 1st March of year 0 is Wednesday */
  32 #define ADJUSTED_EPOCH_WDAY     3
  33 /* there are 97 leap years in 400-year periods. ((400 - 97) * 365 + 97 * 366) */
  34 #define DAYS_PER_ERA            146097L
  35 /* there are 24 leap years in 100-year periods. ((100 - 24) * 365 + 24 * 366) */
  36 #define DAYS_PER_CENTURY        36524L
  37 /* there is one leap year every 4 years */
  38 #define DAYS_PER_4_YEARS        (3 * 365 + 366)
  39 /* number of days in a non-leap year */
  40 #define DAYS_PER_YEAR           365
  41 /* number of days in January */
  42 #define DAYS_IN_JANUARY         31
  43 /* number of days in non-leap February */
  44 #define DAYS_IN_FEBRUARY        28
  45 /* number of years per era */
  46 #define YEARS_PER_ERA           400
  47
  48 struct tm *
  49 gmtime_r (const time_t *__restrict tim_p,
  50         struct tm *__restrict res)
  51 {
  52   long days, rem;
  53   const time_t lcltime = *tim_p;
  54   int era, weekday, year;
  55   unsigned erayear, yearday, month, day;
  56   unsigned long eraday;
  57
  58   days = lcltime / SECSPERDAY + EPOCH_ADJUSTMENT_DAYS;
  59   rem = lcltime % SECSPERDAY;
  60   if (rem < 0)
  61     {
  62       rem += SECSPERDAY;
  63       --days;
  64     }
  65
  66   /* compute hour, min, and sec */
  67   res->tm_hour = (int) (rem / SECSPERHOUR);
  68   rem %= SECSPERHOUR;
  69   res->tm_min = (int) (rem / SECSPERMIN);
  70   res->tm_sec = (int) (rem % SECSPERMIN);
  71
  72   /* compute day of week */
  73   if ((weekday = ((ADJUSTED_EPOCH_WDAY + days) % DAYSPERWEEK)) < 0)
  74     weekday += DAYSPERWEEK;
  75   res->tm_wday = weekday;
  76
  77   /* compute year, month, day & day of year */
  78   /* for description of this algorithm see
  79    * http://howardhinnant.github.io/date_algorithms.html#civil_from_days */
  80   era = (days >= 0 ? days : days - (DAYS_PER_ERA - 1)) / DAYS_PER_ERA;
  81   eraday = days - era * DAYS_PER_ERA;   /* [0, 146096] */
  82   erayear = (eraday - eraday / (DAYS_PER_4_YEARS - 1) + eraday / DAYS_PER_CENTURY -
  83       eraday / (DAYS_PER_ERA - 1)) / 365;       /* [0, 399] */
  84   yearday = eraday - (DAYS_PER_YEAR * erayear + erayear / 4 - erayear / 100);   /* [0, 365] */
  85   month = (5 * yearday + 2) / 153;      /* [0, 11] */
  86   day = yearday - (153 * month + 2) / 5 + 1;    /* [1, 31] */
  87   month += month < 10 ? 2 : -10;
  88   year = ADJUSTED_EPOCH_YEAR + erayear + era * YEARS_PER_ERA + (month <= 1);
  89
  90   res->tm_yday = yearday >= DAYS_PER_YEAR - DAYS_IN_JANUARY - DAYS_IN_FEBRUARY ?
  91       yearday - (DAYS_PER_YEAR - DAYS_IN_JANUARY - DAYS_IN_FEBRUARY) :
  92       yearday + DAYS_IN_JANUARY + DAYS_IN_FEBRUARY + isleap(erayear);
  93   res->tm_year = year - YEAR_BASE;
  94   res->tm_mon = month;
  95   res->tm_mday = day;
  96
  97   res->tm_isdst = 0;
  98
  99   return (res);
 100 }