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  *		(Must be positive.)
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 	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 }
142 EXPORT_SYMBOL(rtc_time64_to_tm);
143 
144 /*
145  * Does the rtc_time represent a valid date/time?
146  */
rtc_valid_tm(struct rtc_time * tm)147 int 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 }
162 EXPORT_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  */
rtc_tm_to_time64(struct rtc_time * tm)168 time64_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 }
173 EXPORT_SYMBOL(rtc_tm_to_time64);
174 
175 /*
176  * Convert rtc_time to ktime
177  */
rtc_tm_to_ktime(struct rtc_time tm)178 ktime_t rtc_tm_to_ktime(struct rtc_time tm)
179 {
180 	return ktime_set(rtc_tm_to_time64(&tm), 0);
181 }
182 EXPORT_SYMBOL_GPL(rtc_tm_to_ktime);
183 
184 /*
185  * Convert ktime to rtc_time
186  */
rtc_ktime_to_tm(ktime_t kt)187 struct 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 }
199 EXPORT_SYMBOL_GPL(rtc_ktime_to_tm);
200