/* * Copyright (C) Igor Sysoev * Copyright (C) NGINX, Inc. */ #include /* 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; }