drivers/rtc/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
  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  */
  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  */
  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  */
  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  */
 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  */
 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  */
 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  */
 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);