LXR linux/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
  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 *              (Must be positive.)
  50 * @tm:         Pointer to the struct rtc_time.
  51 */
  52void 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}
 142EXPORT_SYMBOL(rtc_time64_to_tm);
 143
 144/*
 145 * Does the rtc_time represent a valid date/time?
 146 */
 147int 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}
 162EXPORT_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 */
 168time64_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}
 173EXPORT_SYMBOL(rtc_tm_to_time64);
 174
 175/*
 176 * Convert rtc_time to ktime
 177 */
 178ktime_t rtc_tm_to_ktime(struct rtc_time tm)
 179{
 180        return ktime_set(rtc_tm_to_time64(&tm), 0);
 181}
 182EXPORT_SYMBOL_GPL(rtc_tm_to_ktime);
 183
 184/*
 185 * Convert ktime to rtc_time
 186 */
 187struct 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}
 199EXPORT_SYMBOL_GPL(rtc_ktime_to_tm);
 200