drivers/rtc/lib.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * rtc and date/time utility functions
0004  *
0005  * Copyright (C) 2005-06 Tower Technologies
0006  * Author: Alessandro Zummo <a.zummo@towertech.it>
0007  *
0008  * based on arch/arm/common/rtctime.c and other bits
0009  *
0010  * Author: Cassio Neri <cassio.neri@gmail.com> (rtc_time64_to_tm)
0011  */
0012
0013 #include <linux/export.h>
0014 #include <linux/rtc.h>
0015
0016 static const unsigned char rtc_days_in_month[] = {
0017     31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
0018 };
0019
0020 static const unsigned short rtc_ydays[2][13] = {
0021     /* Normal years */
0022     { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
0023     /* Leap years */
0024     { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
0025 };
0026
0027 /*
0028  * The number of days in the month.
0029  */
0030 int rtc_month_days(unsigned int month, unsigned int year)
0031 {
0032     return rtc_days_in_month[month] + (is_leap_year(year) && month == 1);
0033 }
0034 EXPORT_SYMBOL(rtc_month_days);
0035
0036 /*
0037  * The number of days since January 1. (0 to 365)
0038  */
0039 int rtc_year_days(unsigned int day, unsigned int month, unsigned int year)
0040 {
0041     return rtc_ydays[is_leap_year(year)][month] + day - 1;
0042 }
0043 EXPORT_SYMBOL(rtc_year_days);
0044
0045 /**
0046  * rtc_time64_to_tm - converts time64_t to rtc_time.
0047  *
0048  * @time:   The number of seconds since 01-01-1970 00:00:00.
0049  *      (Must be positive.)
0050  * @tm:     Pointer to the struct rtc_time.
0051  */
0052 void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
0053 {
0054     unsigned int secs;
0055     int days;
0056
0057     u64 u64tmp;
0058     u32 u32tmp, udays, century, day_of_century, year_of_century, year,
0059         day_of_year, month, day;
0060     bool is_Jan_or_Feb, is_leap_year;
0061
0062     /* time must be positive */
0063     days = div_s64_rem(time, 86400, &secs);
0064
0065     /* day of the week, 1970-01-01 was a Thursday */
0066     tm->tm_wday = (days + 4) % 7;
0067
0068     /*
0069      * The following algorithm is, basically, Proposition 6.3 of Neri
0070      * and Schneider [1]. In a few words: it works on the computational
0071      * (fictitious) calendar where the year starts in March, month = 2
0072      * (*), and finishes in February, month = 13. This calendar is
0073      * mathematically convenient because the day of the year does not
0074      * depend on whether the year is leap or not. For instance:
0075      *
0076      * March 1st        0-th day of the year;
0077      * ...
0078      * April 1st        31-st day of the year;
0079      * ...
0080      * January 1st      306-th day of the year; (Important!)
0081      * ...
0082      * February 28th    364-th day of the year;
0083      * February 29th    365-th day of the year (if it exists).
0084      *
0085      * After having worked out the date in the computational calendar
0086      * (using just arithmetics) it's easy to convert it to the
0087      * corresponding date in the Gregorian calendar.
0088      *
0089      * [1] "Euclidean Affine Functions and Applications to Calendar
0090      * Algorithms". https://arxiv.org/abs/2102.06959
0091      *
0092      * (*) The numbering of months follows rtc_time more closely and
0093      * thus, is slightly different from [1].
0094      */
0095
0096     udays       = ((u32) days) + 719468;
0097
0098     u32tmp      = 4 * udays + 3;
0099     century     = u32tmp / 146097;
0100     day_of_century  = u32tmp % 146097 / 4;
0101
0102     u32tmp      = 4 * day_of_century + 3;
0103     u64tmp      = 2939745ULL * u32tmp;
0104     year_of_century = upper_32_bits(u64tmp);
0105     day_of_year = lower_32_bits(u64tmp) / 2939745 / 4;
0106
0107     year        = 100 * century + year_of_century;
0108     is_leap_year    = year_of_century != 0 ?
0109         year_of_century % 4 == 0 : century % 4 == 0;
0110
0111     u32tmp      = 2141 * day_of_year + 132377;
0112     month       = u32tmp >> 16;
0113     day     = ((u16) u32tmp) / 2141;
0114
0115     /*
0116      * Recall that January 01 is the 306-th day of the year in the
0117      * computational (not Gregorian) calendar.
0118      */
0119     is_Jan_or_Feb   = day_of_year >= 306;
0120
0121     /* Converts to the Gregorian calendar. */
0122     year        = year + is_Jan_or_Feb;
0123     month       = is_Jan_or_Feb ? month - 12 : month;
0124     day     = day + 1;
0125
0126     day_of_year = is_Jan_or_Feb ?
0127         day_of_year - 306 : day_of_year + 31 + 28 + is_leap_year;
0128
0129     /* Converts to rtc_time's format. */
0130     tm->tm_year = (int) (year - 1900);
0131     tm->tm_mon  = (int) month;
0132     tm->tm_mday = (int) day;
0133     tm->tm_yday = (int) day_of_year + 1;
0134
0135     tm->tm_hour = secs / 3600;
0136     secs -= tm->tm_hour * 3600;
0137     tm->tm_min = secs / 60;
0138     tm->tm_sec = secs - tm->tm_min * 60;
0139
0140     tm->tm_isdst = 0;
0141 }
0142 EXPORT_SYMBOL(rtc_time64_to_tm);
0143
0144 /*
0145  * Does the rtc_time represent a valid date/time?
0146  */
0147 int rtc_valid_tm(struct rtc_time *tm)
0148 {
0149     if (tm->tm_year < 70 ||
0150         tm->tm_year > (INT_MAX - 1900) ||
0151         ((unsigned int)tm->tm_mon) >= 12 ||
0152         tm->tm_mday < 1 ||
0153         tm->tm_mday > rtc_month_days(tm->tm_mon,
0154                      ((unsigned int)tm->tm_year + 1900)) ||
0155         ((unsigned int)tm->tm_hour) >= 24 ||
0156         ((unsigned int)tm->tm_min) >= 60 ||
0157         ((unsigned int)tm->tm_sec) >= 60)
0158         return -EINVAL;
0159
0160     return 0;
0161 }
0162 EXPORT_SYMBOL(rtc_valid_tm);
0163
0164 /*
0165  * rtc_tm_to_time64 - Converts rtc_time to time64_t.
0166  * Convert Gregorian date to seconds since 01-01-1970 00:00:00.
0167  */
0168 time64_t rtc_tm_to_time64(struct rtc_time *tm)
0169 {
0170     return mktime64(((unsigned int)tm->tm_year + 1900), tm->tm_mon + 1,
0171             tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec);
0172 }
0173 EXPORT_SYMBOL(rtc_tm_to_time64);
0174
0175 /*
0176  * Convert rtc_time to ktime
0177  */
0178 ktime_t rtc_tm_to_ktime(struct rtc_time tm)
0179 {
0180     return ktime_set(rtc_tm_to_time64(&tm), 0);
0181 }
0182 EXPORT_SYMBOL_GPL(rtc_tm_to_ktime);
0183
0184 /*
0185  * Convert ktime to rtc_time
0186  */
0187 struct rtc_time rtc_ktime_to_tm(ktime_t kt)
0188 {
0189     struct timespec64 ts;
0190     struct rtc_time ret;
0191
0192     ts = ktime_to_timespec64(kt);
0193     /* Round up any ns */
0194     if (ts.tv_nsec)
0195         ts.tv_sec++;
0196     rtc_time64_to_tm(ts.tv_sec, &ret);
0197     return ret;
0198 }
0199 EXPORT_SYMBOL_GPL(rtc_ktime_to_tm);