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 days, 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 * Get days and seconds while preserving the sign to
63 * handle negative time values (dates before 1970-01-01)
64 */
65 days = div_s64_rem(time, 86400, &secs);
66
67 /*
68 * We need 0 <= secs < 86400 which isn't given for negative
69 * values of time. Fixup accordingly.
70 */
71 if (secs < 0) {
72 days -= 1;
73 secs += 86400;
74 }
75
76 /* day of the week, 1970-01-01 was a Thursday */
77 tm->tm_wday = (days + 4) % 7;
78 /* Ensure tm_wday is always positive */
79 if (tm->tm_wday < 0)
80 tm->tm_wday += 7;
81
82 /*
83 * The following algorithm is, basically, Proposition 6.3 of Neri
84 * and Schneider [1]. In a few words: it works on the computational
85 * (fictitious) calendar where the year starts in March, month = 2
86 * (*), and finishes in February, month = 13. This calendar is
87 * mathematically convenient because the day of the year does not
88 * depend on whether the year is leap or not. For instance:
89 *
90 * March 1st 0-th day of the year;
91 * ...
92 * April 1st 31-st day of the year;
93 * ...
94 * January 1st 306-th day of the year; (Important!)
95 * ...
96 * February 28th 364-th day of the year;
97 * February 29th 365-th day of the year (if it exists).
98 *
99 * After having worked out the date in the computational calendar
100 * (using just arithmetics) it's easy to convert it to the
101 * corresponding date in the Gregorian calendar.
102 *
103 * [1] "Euclidean Affine Functions and Applications to Calendar
104 * Algorithms". https://arxiv.org/abs/2102.06959
105 *
106 * (*) The numbering of months follows rtc_time more closely and
107 * thus, is slightly different from [1].
108 */
109
110 udays = days + 719468;
111
112 u32tmp = 4 * udays + 3;
113 century = u32tmp / 146097;
114 day_of_century = u32tmp % 146097 / 4;
115
116 u32tmp = 4 * day_of_century + 3;
117 u64tmp = 2939745ULL * u32tmp;
118 year_of_century = upper_32_bits(u64tmp);
119 day_of_year = lower_32_bits(u64tmp) / 2939745 / 4;
120
121 year = 100 * century + year_of_century;
122 is_leap_year = year_of_century != 0 ?
123 year_of_century % 4 == 0 : century % 4 == 0;
124
125 u32tmp = 2141 * day_of_year + 132377;
126 month = u32tmp >> 16;
127 day = ((u16) u32tmp) / 2141;
128
129 /*
130 * Recall that January 01 is the 306-th day of the year in the
131 * computational (not Gregorian) calendar.
132 */
133 is_Jan_or_Feb = day_of_year >= 306;
134
135 /* Converts to the Gregorian calendar. */
136 year = year + is_Jan_or_Feb;
137 month = is_Jan_or_Feb ? month - 12 : month;
138 day = day + 1;
139
140 day_of_year = is_Jan_or_Feb ?
141 day_of_year - 306 : day_of_year + 31 + 28 + is_leap_year;
142
143 /* Converts to rtc_time's format. */
144 tm->tm_year = (int) (year - 1900);
145 tm->tm_mon = (int) month;
146 tm->tm_mday = (int) day;
147 tm->tm_yday = (int) day_of_year + 1;
148
149 tm->tm_hour = secs / 3600;
150 secs -= tm->tm_hour * 3600;
151 tm->tm_min = secs / 60;
152 tm->tm_sec = secs - tm->tm_min * 60;
153
154 tm->tm_isdst = 0;
155 }
156 EXPORT_SYMBOL(rtc_time64_to_tm);
157
158 /*
159 * Does the rtc_time represent a valid date/time?
160 */
rtc_valid_tm(struct rtc_time * tm)161 int rtc_valid_tm(struct rtc_time *tm)
162 {
163 if (tm->tm_year < 70 ||
164 tm->tm_year > (INT_MAX - 1900) ||
165 ((unsigned int)tm->tm_mon) >= 12 ||
166 tm->tm_mday < 1 ||
167 tm->tm_mday > rtc_month_days(tm->tm_mon,
168 ((unsigned int)tm->tm_year + 1900)) ||
169 ((unsigned int)tm->tm_hour) >= 24 ||
170 ((unsigned int)tm->tm_min) >= 60 ||
171 ((unsigned int)tm->tm_sec) >= 60)
172 return -EINVAL;
173
174 return 0;
175 }
176 EXPORT_SYMBOL(rtc_valid_tm);
177
178 /*
179 * rtc_tm_to_time64 - Converts rtc_time to time64_t.
180 * Convert Gregorian date to seconds since 01-01-1970 00:00:00.
181 */
rtc_tm_to_time64(struct rtc_time * tm)182 time64_t rtc_tm_to_time64(struct rtc_time *tm)
183 {
184 return mktime64(((unsigned int)tm->tm_year + 1900), tm->tm_mon + 1,
185 tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec);
186 }
187 EXPORT_SYMBOL(rtc_tm_to_time64);
188
189 /*
190 * Convert rtc_time to ktime
191 */
rtc_tm_to_ktime(struct rtc_time tm)192 ktime_t rtc_tm_to_ktime(struct rtc_time tm)
193 {
194 return ktime_set(rtc_tm_to_time64(&tm), 0);
195 }
196 EXPORT_SYMBOL_GPL(rtc_tm_to_ktime);
197
198 /*
199 * Convert ktime to rtc_time
200 */
rtc_ktime_to_tm(ktime_t kt)201 struct rtc_time rtc_ktime_to_tm(ktime_t kt)
202 {
203 struct timespec64 ts;
204 struct rtc_time ret;
205
206 ts = ktime_to_timespec64(kt);
207 /* Round up any ns */
208 if (ts.tv_nsec)
209 ts.tv_sec++;
210 rtc_time64_to_tm(ts.tv_sec, &ret);
211 return ret;
212 }
213 EXPORT_SYMBOL_GPL(rtc_ktime_to_tm);
214