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102 lines
3.8 KiB
C
102 lines
3.8 KiB
C
/*
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* gmtime_r.c
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* Original Author: Adapted from tzcode maintained by Arthur David Olson.
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* Modifications:
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* - Changed to mktm_r and added __tzcalc_limits - 04/10/02, Jeff Johnston
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* - Fixed bug in mday computations - 08/12/04, Alex Mogilnikov <alx@intellectronika.ru>
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* - Fixed bug in __tzcalc_limits - 08/12/04, Alex Mogilnikov <alx@intellectronika.ru>
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* - Move code from _mktm_r() to gmtime_r() - 05/09/14, Freddie Chopin <freddie_chopin@op.pl>
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* - Fixed bug in calculations for dates after year 2069 or before year 1901. Ideas for
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* solution taken from musl's __secs_to_tm() - 07/12/2014, Freddie Chopin
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* <freddie_chopin@op.pl>
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* - Use faster algorithm from civil_from_days() by Howard Hinnant - 12/06/2014,
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* Freddie Chopin <freddie_chopin@op.pl>
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*
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* Converts the calendar time pointed to by tim_p into a broken-down time
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* expressed as local time. Returns a pointer to a structure containing the
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* broken-down time.
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*/
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#include "local.h"
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/* Move epoch from 01.01.1970 to 01.03.0000 (yes, Year 0) - this is the first
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* day of a 400-year long "era", right after additional day of leap year.
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* This adjustment is required only for date calculation, so instead of
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* modifying time_t value (which would require 64-bit operations to work
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* correctly) it's enough to adjust the calculated number of days since epoch.
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*/
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#define EPOCH_ADJUSTMENT_DAYS 719468L
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/* year to which the adjustment was made */
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#define ADJUSTED_EPOCH_YEAR 0
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/* 1st March of year 0 is Wednesday */
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#define ADJUSTED_EPOCH_WDAY 3
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/* there are 97 leap years in 400-year periods. ((400 - 97) * 365 + 97 * 366) */
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#define DAYS_PER_ERA 146097L
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/* there are 24 leap years in 100-year periods. ((100 - 24) * 365 + 24 * 366) */
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#define DAYS_PER_CENTURY 36524L
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/* there is one leap year every 4 years */
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#define DAYS_PER_4_YEARS (3 * 365 + 366)
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/* number of days in a non-leap year */
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#define DAYS_PER_YEAR 365
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/* number of days in January */
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#define DAYS_IN_JANUARY 31
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/* number of days in non-leap February */
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#define DAYS_IN_FEBRUARY 28
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/* number of years per era */
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#define YEARS_PER_ERA 400
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struct tm *
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_DEFUN (gmtime_r, (tim_p, res),
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_CONST time_t *__restrict tim_p _AND
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struct tm *__restrict res)
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{
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long days, rem;
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_CONST time_t lcltime = *tim_p;
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int era, weekday, year;
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unsigned erayear, yearday, month, day;
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unsigned long eraday;
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days = ((long)lcltime) / SECSPERDAY + EPOCH_ADJUSTMENT_DAYS;
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rem = ((long)lcltime) % SECSPERDAY;
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if (rem < 0)
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{
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rem += SECSPERDAY;
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--days;
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}
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/* compute hour, min, and sec */
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res->tm_hour = (int) (rem / SECSPERHOUR);
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rem %= SECSPERHOUR;
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res->tm_min = (int) (rem / SECSPERMIN);
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res->tm_sec = (int) (rem % SECSPERMIN);
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/* compute day of week */
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if ((weekday = ((ADJUSTED_EPOCH_WDAY + days) % DAYSPERWEEK)) < 0)
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weekday += DAYSPERWEEK;
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res->tm_wday = weekday;
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/* compute year, month, day & day of year */
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/* for description of this algorithm see
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* http://howardhinnant.github.io/date_algorithms.html#civil_from_days */
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era = (days >= 0 ? days : days - (DAYS_PER_ERA - 1)) / DAYS_PER_ERA;
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eraday = days - era * DAYS_PER_ERA; /* [0, 146096] */
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erayear = (eraday - eraday / (DAYS_PER_4_YEARS - 1) + eraday / DAYS_PER_CENTURY -
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eraday / (DAYS_PER_ERA - 1)) / 365; /* [0, 399] */
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yearday = eraday - (DAYS_PER_YEAR * erayear + erayear / 4 - erayear / 100); /* [0, 365] */
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month = (5 * yearday + 2) / 153; /* [0, 11] */
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day = yearday - (153 * month + 2) / 5 + 1; /* [1, 31] */
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month += month < 10 ? 2 : -10;
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year = ADJUSTED_EPOCH_YEAR + erayear + era * YEARS_PER_ERA + (month <= 1);
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res->tm_yday = yearday >= DAYS_PER_YEAR - DAYS_IN_JANUARY - DAYS_IN_FEBRUARY ?
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yearday - (DAYS_PER_YEAR - DAYS_IN_JANUARY - DAYS_IN_FEBRUARY) :
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yearday + DAYS_IN_JANUARY + DAYS_IN_FEBRUARY + isleap(erayear);
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res->tm_year = year - YEAR_BASE;
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res->tm_mon = month;
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res->tm_mday = day;
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res->tm_isdst = 0;
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return (res);
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}
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