xref: /unit/src/nxt_gmtime.c (revision 0:a63ceefd6ab0)
1*0Sigor@sysoev.ru 
2*0Sigor@sysoev.ru /*
3*0Sigor@sysoev.ru  * Copyright (C) Igor Sysoev
4*0Sigor@sysoev.ru  * Copyright (C) NGINX, Inc.
5*0Sigor@sysoev.ru  */
6*0Sigor@sysoev.ru 
7*0Sigor@sysoev.ru #include <nxt_main.h>
8*0Sigor@sysoev.ru 
9*0Sigor@sysoev.ru 
10*0Sigor@sysoev.ru /* The function is valid for positive nxt_time_t only. */
11*0Sigor@sysoev.ru 
12*0Sigor@sysoev.ru void
nxt_gmtime(nxt_time_t s,struct tm * tm)13*0Sigor@sysoev.ru nxt_gmtime(nxt_time_t s, struct tm *tm)
14*0Sigor@sysoev.ru {
15*0Sigor@sysoev.ru     nxt_int_t   yday;
16*0Sigor@sysoev.ru     nxt_uint_t  daytime, mday, mon, year, days, leap;
17*0Sigor@sysoev.ru 
18*0Sigor@sysoev.ru     days = (nxt_uint_t) (s / 86400);
19*0Sigor@sysoev.ru     daytime = (nxt_uint_t) (s % 86400);
20*0Sigor@sysoev.ru 
21*0Sigor@sysoev.ru     /* January 1, 1970 was Thursday. */
22*0Sigor@sysoev.ru     tm->tm_wday = (4 + days) % 7;
23*0Sigor@sysoev.ru 
24*0Sigor@sysoev.ru     /* The algorithm based on Gauss' formula. */
25*0Sigor@sysoev.ru 
26*0Sigor@sysoev.ru     /* Days since March 1, 1 BCE. */
27*0Sigor@sysoev.ru     days = days - (31 + 28) + 719527;
28*0Sigor@sysoev.ru 
29*0Sigor@sysoev.ru     /*
30*0Sigor@sysoev.ru      * The "days" should be adjusted by 1 only, however some March 1st's
31*0Sigor@sysoev.ru      * go to previous year, so "days" are adjusted by 2.  This also shifts
32*0Sigor@sysoev.ru      * the last February days to the next year, but this is catched by
33*0Sigor@sysoev.ru      * negative "yday".
34*0Sigor@sysoev.ru      */
35*0Sigor@sysoev.ru     year = (days + 2) * 400 / (365 * 400 + 100 - 4 + 1);
36*0Sigor@sysoev.ru 
37*0Sigor@sysoev.ru     yday = days - (365 * year + year / 4 - year / 100 + year / 400);
38*0Sigor@sysoev.ru 
39*0Sigor@sysoev.ru     leap = (year % 4 == 0) && (year % 100 || (year % 400 == 0));
40*0Sigor@sysoev.ru 
41*0Sigor@sysoev.ru     if (yday < 0) {
42*0Sigor@sysoev.ru         yday = 365 + leap + yday;
43*0Sigor@sysoev.ru         year--;
44*0Sigor@sysoev.ru     }
45*0Sigor@sysoev.ru 
46*0Sigor@sysoev.ru     /*
47*0Sigor@sysoev.ru      * An empirical formula that maps "yday" to month.
48*0Sigor@sysoev.ru      * There are at least 10 variants, some of them are:
49*0Sigor@sysoev.ru      *     mon = (yday + 31) * 15 / 459
50*0Sigor@sysoev.ru      *     mon = (yday + 31) * 17 / 520
51*0Sigor@sysoev.ru      *     mon = (yday + 31) * 20 / 612
52*0Sigor@sysoev.ru      */
53*0Sigor@sysoev.ru 
54*0Sigor@sysoev.ru     mon = (yday + 31) * 10 / 306;
55*0Sigor@sysoev.ru 
56*0Sigor@sysoev.ru     /* The Gauss' formula that evaluates days before month. */
57*0Sigor@sysoev.ru 
58*0Sigor@sysoev.ru     mday = yday - (367 * mon / 12 - 30) + 1;
59*0Sigor@sysoev.ru 
60*0Sigor@sysoev.ru     if (yday >= 306) {
61*0Sigor@sysoev.ru         year++;
62*0Sigor@sysoev.ru         mon -= 11;
63*0Sigor@sysoev.ru         yday -= 306;
64*0Sigor@sysoev.ru 
65*0Sigor@sysoev.ru     } else {
66*0Sigor@sysoev.ru         mon++;
67*0Sigor@sysoev.ru         yday += 31 + 28 + leap;
68*0Sigor@sysoev.ru     }
69*0Sigor@sysoev.ru 
70*0Sigor@sysoev.ru     tm->tm_mday = mday;
71*0Sigor@sysoev.ru     tm->tm_mon = mon;
72*0Sigor@sysoev.ru     tm->tm_year = year - 1900;
73*0Sigor@sysoev.ru     tm->tm_yday = yday;
74*0Sigor@sysoev.ru 
75*0Sigor@sysoev.ru     tm->tm_hour = daytime / 3600;
76*0Sigor@sysoev.ru     daytime %= 3600;
77*0Sigor@sysoev.ru     tm->tm_min = daytime / 60;
78*0Sigor@sysoev.ru     tm->tm_sec = daytime % 60;
79*0Sigor@sysoev.ru }
80