xref: /openbmc/u-boot/drivers/rtc/date.c (revision c5fcd9e5)
1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  * (C) Copyright 2001
4  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
5  */
6 
7 #include <common.h>
8 #include <command.h>
9 #include <errno.h>
10 #include <rtc.h>
11 
12 #if defined(CONFIG_CMD_DATE) || defined(CONFIG_DM_RTC) || \
13 				defined(CONFIG_TIMESTAMP)
14 
15 #define FEBRUARY		2
16 #define	STARTOFTIME		1970
17 #define SECDAY			86400L
18 #define SECYR			(SECDAY * 365)
19 #define	leapyear(year)		((year) % 4 == 0)
20 #define	days_in_year(a)		(leapyear(a) ? 366 : 365)
21 #define	days_in_month(a)	(month_days[(a) - 1])
22 
23 static int month_offset[] = {
24 	0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
25 };
26 
27 /*
28  * This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
29  */
30 int rtc_calc_weekday(struct rtc_time *tm)
31 {
32 	int leaps_to_date;
33 	int last_year;
34 	int day;
35 
36 	if (tm->tm_year < 1753)
37 		return -1;
38 	last_year = tm->tm_year - 1;
39 
40 	/* Number of leap corrections to apply up to end of last year */
41 	leaps_to_date = last_year / 4 - last_year / 100 + last_year / 400;
42 
43 	/*
44 	 * This year is a leap year if it is divisible by 4 except when it is
45 	 * divisible by 100 unless it is divisible by 400
46 	 *
47 	 * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 is.
48 	 */
49 	if (tm->tm_year % 4 == 0 &&
50 	    ((tm->tm_year % 100 != 0) || (tm->tm_year % 400 == 0)) &&
51 	    tm->tm_mon > 2) {
52 		/* We are past Feb. 29 in a leap year */
53 		day = 1;
54 	} else {
55 		day = 0;
56 	}
57 
58 	day += last_year * 365 + leaps_to_date + month_offset[tm->tm_mon - 1] +
59 			tm->tm_mday;
60 	tm->tm_wday = day % 7;
61 
62 	return 0;
63 }
64 
65 /*
66  * Converts Gregorian date to seconds since 1970-01-01 00:00:00.
67  * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
68  * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
69  *
70  * [For the Julian calendar (which was used in Russia before 1917,
71  * Britain & colonies before 1752, anywhere else before 1582,
72  * and is still in use by some communities) leave out the
73  * -year / 100 + year / 400 terms, and add 10.]
74  *
75  * This algorithm was first published by Gauss (I think).
76  *
77  * WARNING: this function will overflow on 2106-02-07 06:28:16 on
78  * machines where long is 32-bit! (However, as time_t is signed, we
79  * will already get problems at other places on 2038-01-19 03:14:08)
80  */
81 unsigned long rtc_mktime(const struct rtc_time *tm)
82 {
83 	int mon = tm->tm_mon;
84 	int year = tm->tm_year;
85 	int days, hours;
86 
87 	mon -= 2;
88 	if (0 >= (int)mon) {	/* 1..12 -> 11, 12, 1..10 */
89 		mon += 12;	/* Puts Feb last since it has leap day */
90 		year -= 1;
91 	}
92 
93 	days = (unsigned long)(year / 4 - year / 100 + year / 400 +
94 			367 * mon / 12 + tm->tm_mday) +
95 			year * 365 - 719499;
96 	hours = days * 24 + tm->tm_hour;
97 	return (hours * 60 + tm->tm_min) * 60 + tm->tm_sec;
98 }
99 
100 #endif
101