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