lib.c

  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 *		Works for values since at least 1900
 50 * @tm:		Pointer to the struct rtc_time.
 51 */
 52void 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}
154EXPORT_SYMBOL(rtc_time64_to_tm);
155
156/*
157 * Does the rtc_time represent a valid date/time?
158 */
159int 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}
174EXPORT_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 */
180time64_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}
185EXPORT_SYMBOL(rtc_tm_to_time64);
186
187/*
188 * Convert rtc_time to ktime
189 */
190ktime_t rtc_tm_to_ktime(struct rtc_time tm)
191{
192	return ktime_set(rtc_tm_to_time64(&tm), 0);
193}
194EXPORT_SYMBOL_GPL(rtc_tm_to_ktime);
195
196/*
197 * Convert ktime to rtc_time
198 */
199struct 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}
211EXPORT_SYMBOL_GPL(rtc_ktime_to_tm);