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 <command.h>
8#include <errno.h>
9#include <rtc.h>
10#include <linux/time.h>
11
12#define FEBRUARY		2
13#define	STARTOFTIME		1970
14#define SECDAY			86400L
15#define SECYR			(SECDAY * 365)
16#define	leapyear(year)		((year) % 4 == 0)
17#define	days_in_year(a)		(leapyear(a) ? 366 : 365)
18#define	days_in_month(a)	(month_days[(a) - 1])
19
20static int month_offset[] = {
21	0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
22};
23
24/*
25 * This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
26 */
27int rtc_calc_weekday(struct rtc_time *tm)
28{
29	int leaps_to_date;
30	int last_year;
31	int day;
32
33	if (tm->tm_year < 1753)
34		return -1;
35	last_year = tm->tm_year - 1;
36
37	/* Number of leap corrections to apply up to end of last year */
38	leaps_to_date = last_year / 4 - last_year / 100 + last_year / 400;
39
40	/*
41	 * This year is a leap year if it is divisible by 4 except when it is
42	 * divisible by 100 unless it is divisible by 400
43	 *
44	 * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 is.
45	 */
46	if (tm->tm_year % 4 == 0 &&
47	    ((tm->tm_year % 100 != 0) || (tm->tm_year % 400 == 0)) &&
48	    tm->tm_mon > 2) {
49		/* We are past Feb. 29 in a leap year */
50		day = 1;
51	} else {
52		day = 0;
53	}
54
55	day += last_year * 365 + leaps_to_date + month_offset[tm->tm_mon - 1] +
56			tm->tm_mday;
57	tm->tm_wday = day % 7;
58
59	return 0;
60}
61
62/*
63 * Converts Gregorian date to seconds since 1970-01-01 00:00:00.
64 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
65 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
66 *
67 * [For the Julian calendar (which was used in Russia before 1917,
68 * Britain & colonies before 1752, anywhere else before 1582,
69 * and is still in use by some communities) leave out the
70 * -year / 100 + year / 400 terms, and add 10.]
71 *
72 * This algorithm was first published by Gauss (I think).
73 */
74time64_t rtc_mktime(const struct rtc_time *tm)
75{
76	int mon = tm->tm_mon;
77	int year = tm->tm_year;
78	unsigned long days;
79	time64_t hours;
80
81	mon -= 2;
82	if (0 >= mon) {		/* 1..12 -> 11, 12, 1..10 */
83		mon += 12;	/* Puts Feb last since it has leap day */
84		year -= 1;
85	}
86
87	days = (unsigned long)(year / 4 - year / 100 + year / 400 +
88			367 * mon / 12 + tm->tm_mday) +
89			year * 365 - 719499;
90	hours = days * 24 + tm->tm_hour;
91	return (hours * 60 + tm->tm_min) * 60 + tm->tm_sec;
92}
93
94/* for compatibility with linux code */
95time64_t mktime64(const unsigned int year, const unsigned int mon,
96		  const unsigned int day, const unsigned int hour,
97		  const unsigned int min, const unsigned int sec)
98{
99	struct rtc_time time;
100
101	time.tm_year = year;
102	time.tm_mon = mon;
103	time.tm_mday = day;
104	time.tm_hour = hour;
105	time.tm_min = min;
106	time.tm_sec = sec;
107
108	return rtc_mktime((const struct rtc_time *)&time);
109}
110