1// SPDX-License-Identifier: GPL-2.0
2/*
3 * rtc and date/time utility functions
4 *
5 * Copyright (C) 2005-06 Tower Technologies
6 * Author: Alessandro Zummo <a.zummo@towertech.it>
7 *
8 * based on arch/arm/common/rtctime.c and other bits
9 *
10 * Author: Cassio Neri <cassio.neri@gmail.com> (rtc_time64_to_tm)
11 */
12
13#include <linux/export.h>
14#include <linux/rtc.h>
15
16static const unsigned char rtc_days_in_month[] = {
17	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
18};
19
20static const unsigned short rtc_ydays[2][13] = {
21	/* Normal years */
22	{ 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
23	/* Leap years */
24	{ 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
25};
26
27/*
28 * The number of days in the month.
29 */
30int rtc_month_days(unsigned int month, unsigned int year)
31{
32	return rtc_days_in_month[month] + (is_leap_year(year) && month == 1);
33}
34EXPORT_SYMBOL(rtc_month_days);
35
36/*
37 * The number of days since January 1. (0 to 365)
38 */
39int rtc_year_days(unsigned int day, unsigned int month, unsigned int year)
40{
41	return rtc_ydays[is_leap_year(year)][month] + day - 1;
42}
43EXPORT_SYMBOL(rtc_year_days);
44
45/**
46 * rtc_time64_to_tm - converts time64_t to rtc_time.
47 *
48 * @time:	The number of seconds since 01-01-1970 00:00:00.
49 *		(Must be positive.)
50 * @tm:		Pointer to the struct rtc_time.
51 */
52void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
53{
54	unsigned int secs;
55	int days;
56
57	u64 u64tmp;
58	u32 u32tmp, udays, century, day_of_century, year_of_century, year,
59		day_of_year, month, day;
60	bool is_Jan_or_Feb, is_leap_year;
61
62	/* time must be positive */
63	days = div_s64_rem(time, 86400, &secs);
64
65	/* day of the week, 1970-01-01 was a Thursday */
66	tm->tm_wday = (days + 4) % 7;
67
68	/*
69	 * The following algorithm is, basically, Proposition 6.3 of Neri
70	 * and Schneider [1]. In a few words: it works on the computational
71	 * (fictitious) calendar where the year starts in March, month = 2
72	 * (*), and finishes in February, month = 13. This calendar is
73	 * mathematically convenient because the day of the year does not
74	 * depend on whether the year is leap or not. For instance:
75	 *
76	 * March 1st		0-th day of the year;
77	 * ...
78	 * April 1st		31-st day of the year;
79	 * ...
80	 * January 1st		306-th day of the year; (Important!)
81	 * ...
82	 * February 28th	364-th day of the year;
83	 * February 29th	365-th day of the year (if it exists).
84	 *
85	 * After having worked out the date in the computational calendar
86	 * (using just arithmetics) it's easy to convert it to the
87	 * corresponding date in the Gregorian calendar.
88	 *
89	 * [1] "Euclidean Affine Functions and Applications to Calendar
90	 * Algorithms". https://arxiv.org/abs/2102.06959
91	 *
92	 * (*) The numbering of months follows rtc_time more closely and
93	 * thus, is slightly different from [1].
94	 */
95
96	udays		= ((u32) days) + 719468;
97
98	u32tmp		= 4 * udays + 3;
99	century		= u32tmp / 146097;
100	day_of_century	= u32tmp % 146097 / 4;
101
102	u32tmp		= 4 * day_of_century + 3;
103	u64tmp		= 2939745ULL * u32tmp;
104	year_of_century	= upper_32_bits(u64tmp);
105	day_of_year	= lower_32_bits(u64tmp) / 2939745 / 4;
106
107	year		= 100 * century + year_of_century;
108	is_leap_year	= year_of_century != 0 ?
109		year_of_century % 4 == 0 : century % 4 == 0;
110
111	u32tmp		= 2141 * day_of_year + 132377;
112	month		= u32tmp >> 16;
113	day		= ((u16) u32tmp) / 2141;
114
115	/*
116	 * Recall that January 01 is the 306-th day of the year in the
117	 * computational (not Gregorian) calendar.
118	 */
119	is_Jan_or_Feb	= day_of_year >= 306;
120
121	/* Converts to the Gregorian calendar. */
122	year		= year + is_Jan_or_Feb;
123	month		= is_Jan_or_Feb ? month - 12 : month;
124	day		= day + 1;
125
126	day_of_year	= is_Jan_or_Feb ?
127		day_of_year - 306 : day_of_year + 31 + 28 + is_leap_year;
128
129	/* Converts to rtc_time's format. */
130	tm->tm_year	= (int) (year - 1900);
131	tm->tm_mon	= (int) month;
132	tm->tm_mday	= (int) day;
133	tm->tm_yday	= (int) day_of_year + 1;
134
135	tm->tm_hour = secs / 3600;
136	secs -= tm->tm_hour * 3600;
137	tm->tm_min = secs / 60;
138	tm->tm_sec = secs - tm->tm_min * 60;
139
140	tm->tm_isdst = 0;
141}
142EXPORT_SYMBOL(rtc_time64_to_tm);
143
144/*
145 * Does the rtc_time represent a valid date/time?
146 */
147int rtc_valid_tm(struct rtc_time *tm)
148{
149	if (tm->tm_year < 70 ||
150	    tm->tm_year > (INT_MAX - 1900) ||
151	    ((unsigned int)tm->tm_mon) >= 12 ||
152	    tm->tm_mday < 1 ||
153	    tm->tm_mday > rtc_month_days(tm->tm_mon,
154					 ((unsigned int)tm->tm_year + 1900)) ||
155	    ((unsigned int)tm->tm_hour) >= 24 ||
156	    ((unsigned int)tm->tm_min) >= 60 ||
157	    ((unsigned int)tm->tm_sec) >= 60)
158		return -EINVAL;
159
160	return 0;
161}
162EXPORT_SYMBOL(rtc_valid_tm);
163
164/*
165 * rtc_tm_to_time64 - Converts rtc_time to time64_t.
166 * Convert Gregorian date to seconds since 01-01-1970 00:00:00.
167 */
168time64_t rtc_tm_to_time64(struct rtc_time *tm)
169{
170	return mktime64(((unsigned int)tm->tm_year + 1900), tm->tm_mon + 1,
171			tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec);
172}
173EXPORT_SYMBOL(rtc_tm_to_time64);
174
175/*
176 * Convert rtc_time to ktime
177 */
178ktime_t rtc_tm_to_ktime(struct rtc_time tm)
179{
180	return ktime_set(rtc_tm_to_time64(&tm), 0);
181}
182EXPORT_SYMBOL_GPL(rtc_tm_to_ktime);
183
184/*
185 * Convert ktime to rtc_time
186 */
187struct rtc_time rtc_ktime_to_tm(ktime_t kt)
188{
189	struct timespec64 ts;
190	struct rtc_time ret;
191
192	ts = ktime_to_timespec64(kt);
193	/* Round up any ns */
194	if (ts.tv_nsec)
195		ts.tv_sec++;
196	rtc_time64_to_tm(ts.tv_sec, &ret);
197	return ret;
198}
199EXPORT_SYMBOL_GPL(rtc_ktime_to_tm);
200