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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>
*
* 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 01.03.2000 - this is the first day of new
* 400-year long cycle, 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 11017
/* year to which the adjustment was made */
#define ADJUSTED_EPOCH_YEAR 2000
/* 1st March of 2000 is Wednesday */
#define ADJUSTED_EPOCH_WDAY 3
/* there are 97 leap years in 400-year periods. ((400 - 97) * 365 + 97 * 366) */
#define DAYS_PER_400_YEARS 146097L
/* there are 24 leap years in 100-year periods. ((100 - 24) * 365 + 24 * 366) */
#define DAYS_PER_100_YEARS 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
struct tm *
_DEFUN (gmtime_r, (tim_p, res),
_CONST time_t *__restrict tim_p _AND
struct tm *__restrict res)
{
long days, rem;
_CONST time_t lcltime = *tim_p;
int year, month, yearday, weekday;
int years400, years100, years4, remainingyears;
int yearleap;
_CONST int *ip;
days = ((long)lcltime) / SECSPERDAY - EPOCH_ADJUSTMENT_DAYS;
rem = ((long)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 & day of year */
years400 = days / DAYS_PER_400_YEARS;
days -= years400 * DAYS_PER_400_YEARS;
/* simplify by making the values positive */
if (days < 0)
{
days += DAYS_PER_400_YEARS;
--years400;
}
years100 = days / DAYS_PER_100_YEARS;
if (years100 == 4) /* required for proper day of year calculation */
--years100;
days -= years100 * DAYS_PER_100_YEARS;
years4 = days / DAYS_PER_4_YEARS;
days -= years4 * DAYS_PER_4_YEARS;
remainingyears = days / DAYS_PER_YEAR;
if (remainingyears == 4) /* required for proper day of year calculation */
--remainingyears;
days -= remainingyears * DAYS_PER_YEAR;
year = ADJUSTED_EPOCH_YEAR + years400 * 400 + years100 * 100 + years4 * 4 +
remainingyears;
/* If remainingyears is zero, it means that the years were completely
* "consumed" by modulo calculations by 400, 100 and 4, so the year is:
* 1. a multiple of 4, but not a multiple of 100 or 400 - it's a leap year,
* 2. a multiple of 4 and 100, but not a multiple of 400 - it's not a leap
* year,
* 3. a multiple of 4, 100 and 400 - it's a leap year.
* If years4 is non-zero, it means that the year is not a multiple of 100 or
* 400 (case 1), so it's a leap year. If years100 is zero (and years4 is zero
* - due to short-circuiting), it means that the year is a multiple of 400
* (case 3), so it's also a leap year. */
yearleap = remainingyears == 0 && (years4 != 0 || years100 == 0);
/* adjust back to 1st January */
yearday = days + DAYS_IN_JANUARY + DAYS_IN_FEBRUARY + yearleap;
if (yearday >= DAYS_PER_YEAR + yearleap)
{
yearday -= DAYS_PER_YEAR + yearleap;
++year;
}
res->tm_yday = yearday;
res->tm_year = year - YEAR_BASE;
/* Because "days" is the number of days since 1st March, the additional leap
* day (29th of February) is the last possible day, so it doesn't matter much
* whether the year is actually leap or not. */
ip = __month_lengths[1];
month = 2;
while (days >= ip[month])
{
days -= ip[month];
if (++month >= MONSPERYEAR)
month = 0;
}
res->tm_mon = month;
res->tm_mday = days + 1;
res->tm_isdst = 0;
return (res);
}
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