xref: /linux/drivers/rtc/lib.c (revision d2eedaa3909be9102d648a4a0a50ccf64f96c54f)
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 
16 static const unsigned char rtc_days_in_month[] = {
17 	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
18 };
19 
20 static 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  */
rtc_month_days(unsigned int month,unsigned int year)30 int rtc_month_days(unsigned int month, unsigned int year)
31 {
32 	return rtc_days_in_month[month] + (is_leap_year(year) && month == 1);
33 }
34 EXPORT_SYMBOL(rtc_month_days);
35 
36 /*
37  * The number of days since January 1. (0 to 365)
38  */
rtc_year_days(unsigned int day,unsigned int month,unsigned int year)39 int 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 }
43 EXPORT_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  *		Works for values since at least 1900
50  * @tm:		Pointer to the struct rtc_time.
51  */
rtc_time64_to_tm(time64_t time,struct rtc_time * tm)52 void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
53 {
54 	int secs;
55 
56 	u64 u64tmp;
57 	u32 u32tmp, udays, century, day_of_century, year_of_century, year,
58 		day_of_year, month, day;
59 	bool is_Jan_or_Feb, is_leap_year;
60 
61 	/*
62 	 * The time represented by `time` is given in seconds since 1970-01-01
63 	 * (UTC). As the division done below might misbehave for negative
64 	 * values, we convert it to seconds since 0000-03-01 and then assume it
65 	 * will be non-negative.
66 	 * Below we do 4 * udays + 3 which should fit into a 32 bit unsigned
67 	 * variable. So the latest date this algorithm works for is 1073741823
68 	 * days after 0000-03-01 which is in the year 2939805.
69 	 */
70 	time += (u64)719468 * 86400;
71 
72 	udays = div_s64_rem(time, 86400, &secs);
73 
74 	/*
75 	 * day of the week, 0000-03-01 was a Wednesday (in the proleptic
76 	 * Gregorian calendar)
77 	 */
78 	tm->tm_wday = (udays + 3) % 7;
79 
80 	/*
81 	 * The following algorithm is, basically, Figure 12 of Neri
82 	 * and Schneider [1]. In a few words: it works on the computational
83 	 * (fictitious) calendar where the year starts in March, month = 2
84 	 * (*), and finishes in February, month = 13. This calendar is
85 	 * mathematically convenient because the day of the year does not
86 	 * depend on whether the year is leap or not. For instance:
87 	 *
88 	 * March 1st		0-th day of the year;
89 	 * ...
90 	 * April 1st		31-st day of the year;
91 	 * ...
92 	 * January 1st		306-th day of the year; (Important!)
93 	 * ...
94 	 * February 28th	364-th day of the year;
95 	 * February 29th	365-th day of the year (if it exists).
96 	 *
97 	 * After having worked out the date in the computational calendar
98 	 * (using just arithmetics) it's easy to convert it to the
99 	 * corresponding date in the Gregorian calendar.
100 	 *
101 	 * [1] Neri C, Schneider L. Euclidean affine functions and their
102 	 *     application to calendar algorithms. Softw Pract Exper.
103 	 *     2023;53(4):937-970. doi: 10.1002/spe.3172
104 	 *     https://doi.org/10.1002/spe.3172
105 	 *
106 	 * (*) The numbering of months follows rtc_time more closely and
107 	 * thus, is slightly different from [1].
108 	 */
109 
110 	u32tmp		= 4 * udays + 3;
111 	century		= u32tmp / 146097;
112 	day_of_century	= u32tmp % 146097 / 4;
113 
114 	u32tmp		= 4 * day_of_century + 3;
115 	u64tmp		= 2939745ULL * u32tmp;
116 	year_of_century	= upper_32_bits(u64tmp);
117 	day_of_year	= lower_32_bits(u64tmp) / 2939745 / 4;
118 
119 	year		= 100 * century + year_of_century;
120 	is_leap_year	= year_of_century != 0 ?
121 		year_of_century % 4 == 0 : century % 4 == 0;
122 
123 	u32tmp		= 2141 * day_of_year + 132377;
124 	month		= u32tmp >> 16;
125 	day		= ((u16) u32tmp) / 2141;
126 
127 	/*
128 	 * Recall that January 01 is the 306-th day of the year in the
129 	 * computational (not Gregorian) calendar.
130 	 */
131 	is_Jan_or_Feb	= day_of_year >= 306;
132 
133 	/* Converts to the Gregorian calendar. */
134 	year		= year + is_Jan_or_Feb;
135 	month		= is_Jan_or_Feb ? month - 12 : month;
136 	day		= day + 1;
137 
138 	day_of_year	= is_Jan_or_Feb ?
139 		day_of_year - 306 : day_of_year + 31 + 28 + is_leap_year;
140 
141 	/* Converts to rtc_time's format. */
142 	tm->tm_year	= (int) (year - 1900);
143 	tm->tm_mon	= (int) month;
144 	tm->tm_mday	= (int) day;
145 	tm->tm_yday	= (int) day_of_year + 1;
146 
147 	tm->tm_hour = secs / 3600;
148 	secs -= tm->tm_hour * 3600;
149 	tm->tm_min = secs / 60;
150 	tm->tm_sec = secs - tm->tm_min * 60;
151 
152 	tm->tm_isdst = 0;
153 }
154 EXPORT_SYMBOL(rtc_time64_to_tm);
155 
156 /*
157  * Does the rtc_time represent a valid date/time?
158  */
rtc_valid_tm(struct rtc_time * tm)159 int rtc_valid_tm(struct rtc_time *tm)
160 {
161 	if (tm->tm_year < 70 ||
162 	    tm->tm_year > (INT_MAX - 1900) ||
163 	    ((unsigned int)tm->tm_mon) >= 12 ||
164 	    tm->tm_mday < 1 ||
165 	    tm->tm_mday > rtc_month_days(tm->tm_mon,
166 					 ((unsigned int)tm->tm_year + 1900)) ||
167 	    ((unsigned int)tm->tm_hour) >= 24 ||
168 	    ((unsigned int)tm->tm_min) >= 60 ||
169 	    ((unsigned int)tm->tm_sec) >= 60)
170 		return -EINVAL;
171 
172 	return 0;
173 }
174 EXPORT_SYMBOL(rtc_valid_tm);
175 
176 /*
177  * rtc_tm_to_time64 - Converts rtc_time to time64_t.
178  * Convert Gregorian date to seconds since 01-01-1970 00:00:00.
179  */
rtc_tm_to_time64(struct rtc_time * tm)180 time64_t rtc_tm_to_time64(struct rtc_time *tm)
181 {
182 	return mktime64(((unsigned int)tm->tm_year + 1900), tm->tm_mon + 1,
183 			tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec);
184 }
185 EXPORT_SYMBOL(rtc_tm_to_time64);
186 
187 /*
188  * Convert rtc_time to ktime
189  */
rtc_tm_to_ktime(struct rtc_time tm)190 ktime_t rtc_tm_to_ktime(struct rtc_time tm)
191 {
192 	return ktime_set(rtc_tm_to_time64(&tm), 0);
193 }
194 EXPORT_SYMBOL_GPL(rtc_tm_to_ktime);
195 
196 /*
197  * Convert ktime to rtc_time
198  */
rtc_ktime_to_tm(ktime_t kt)199 struct rtc_time rtc_ktime_to_tm(ktime_t kt)
200 {
201 	struct timespec64 ts;
202 	struct rtc_time ret;
203 
204 	ts = ktime_to_timespec64(kt);
205 	/* Round up any ns */
206 	if (ts.tv_nsec)
207 		ts.tv_sec++;
208 	rtc_time64_to_tm(ts.tv_sec, &ret);
209 	return ret;
210 }
211 EXPORT_SYMBOL_GPL(rtc_ktime_to_tm);
212