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/*
* Copyright (C) Igor Sysoev
* Copyright (C) NGINX, Inc.
*/
#include <nxt_main.h>
/* The function is valid for positive nxt_time_t only. */
void
nxt_gmtime(nxt_time_t s, struct tm *tm)
{
nxt_int_t yday;
nxt_uint_t daytime, mday, mon, year, days, leap;
days = (nxt_uint_t) (s / 86400);
daytime = (nxt_uint_t) (s % 86400);
/* January 1, 1970 was Thursday. */
tm->tm_wday = (4 + days) % 7;
/* The algorithm based on Gauss' formula. */
/* Days since March 1, 1 BCE. */
days = days - (31 + 28) + 719527;
/*
* The "days" should be adjusted by 1 only, however some March 1st's
* go to previous year, so "days" are adjusted by 2. This also shifts
* the last February days to the next year, but this is catched by
* negative "yday".
*/
year = (days + 2) * 400 / (365 * 400 + 100 - 4 + 1);
yday = days - (365 * year + year / 4 - year / 100 + year / 400);
leap = (year % 4 == 0) && (year % 100 || (year % 400 == 0));
if (yday < 0) {
yday = 365 + leap + yday;
year--;
}
/*
* An empirical formula that maps "yday" to month.
* There are at least 10 variants, some of them are:
* mon = (yday + 31) * 15 / 459
* mon = (yday + 31) * 17 / 520
* mon = (yday + 31) * 20 / 612
*/
mon = (yday + 31) * 10 / 306;
/* The Gauss' formula that evaluates days before month. */
mday = yday - (367 * mon / 12 - 30) + 1;
if (yday >= 306) {
year++;
mon -= 11;
yday -= 306;
} else {
mon++;
yday += 31 + 28 + leap;
}
tm->tm_mday = mday;
tm->tm_mon = mon;
tm->tm_year = year - 1900;
tm->tm_yday = yday;
tm->tm_hour = daytime / 3600;
daytime %= 3600;
tm->tm_min = daytime / 60;
tm->tm_sec = daytime % 60;
}
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