1
2 /*
3 * Copyright (C) Igor Sysoev
4 * Copyright (C) NGINX, Inc.
5 */
6
7 #include <nxt_main.h>
8
9
10 /* The function is valid for positive nxt_time_t only. */
11
12 void
nxt_gmtime(nxt_time_t s,struct tm * tm)13 nxt_gmtime(nxt_time_t s, struct tm *tm)
14 {
15 nxt_int_t yday;
16 nxt_uint_t daytime, mday, mon, year, days, leap;
17
18 days = (nxt_uint_t) (s / 86400);
19 daytime = (nxt_uint_t) (s % 86400);
20
21 /* January 1, 1970 was Thursday. */
22 tm->tm_wday = (4 + days) % 7;
23
24 /* The algorithm based on Gauss' formula. */
25
26 /* Days since March 1, 1 BCE. */
27 days = days - (31 + 28) + 719527;
28
29 /*
30 * The "days" should be adjusted by 1 only, however some March 1st's
31 * go to previous year, so "days" are adjusted by 2. This also shifts
32 * the last February days to the next year, but this is catched by
33 * negative "yday".
34 */
35 year = (days + 2) * 400 / (365 * 400 + 100 - 4 + 1);
36
37 yday = days - (365 * year + year / 4 - year / 100 + year / 400);
38
39 leap = (year % 4 == 0) && (year % 100 || (year % 400 == 0));
40
41 if (yday < 0) {
42 yday = 365 + leap + yday;
43 year--;
44 }
45
46 /*
47 * An empirical formula that maps "yday" to month.
48 * There are at least 10 variants, some of them are:
49 * mon = (yday + 31) * 15 / 459
50 * mon = (yday + 31) * 17 / 520
51 * mon = (yday + 31) * 20 / 612
52 */
53
54 mon = (yday + 31) * 10 / 306;
55
56 /* The Gauss' formula that evaluates days before month. */
57
58 mday = yday - (367 * mon / 12 - 30) + 1;
59
60 if (yday >= 306) {
61 year++;
62 mon -= 11;
63 yday -= 306;
64
65 } else {
66 mon++;
67 yday += 31 + 28 + leap;
68 }
69
70 tm->tm_mday = mday;
71 tm->tm_mon = mon;
72 tm->tm_year = year - 1900;
73 tm->tm_yday = yday;
74
75 tm->tm_hour = daytime / 3600;
76 daytime %= 3600;
77 tm->tm_min = daytime / 60;
78 tm->tm_sec = daytime % 60;
79 }
80