rtc.c

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/* SPDX-License-Identifier: GPL-2.0-or-later */
 
/*
 * From U-Boot 2016.05
 */
 
#include <console/console.h>
#include <rtc.h>
 
#define FEBRUARY                2
#define STARTOFTIME             1970
#define SECDAY                  86400L
#define SECYR                   (SECDAY * 365)
#define LEAP_YEAR(year)         (((year) % 4 == 0 && (year) % 100 != 0) || (year) % 400 == 0)
#define DAYS_IN_YEAR(a)         (LEAP_YEAR(a) ? 366 : 365)
#define DAYS_IN_MONTH(a)        (month_days[(a) - 1])
 
static const char *const weekdays[] = {
        "Sun", "Mon", "Tues", "Wednes", "Thurs", "Fri", "Satur"
};
 
/* Zeller's rule */
static int rtc_calc_weekday(struct rtc_time *tm)
{
        /* In Zeller's rule, January and February are treated as if they
           are months 13 and 14 of the previous year (March is still month 3) */
        const int zyear = ((tm->mon < 3) ? tm->year - 1 : tm->year);
        const int q = tm->mday;
        const int m = (tm->mon < 3) ? tm->mon + 12 : tm->mon;
        const int K = zyear % 100;
        const int J = zyear / 100;
 
        /*
         * Because of the way the modulo operator works with negative numbers,
         * the traditional formulation of Zeller's rule must be modified
         * slightly to make the numerator positive (i.e., add 5J instead of
         * subtracting 2J).  Also subtract 1 so that Sunday is day 0.
         */
        const int h = (q + (13 * (m + 1)) / 5
                       + K + (K / 4) + (J / 4) + (5 * J) - 1) % 7;
 
        tm->wday = h;
        return 0;
}
 
int rtc_to_tm(int tim, struct rtc_time *tm)
{
        int month_days[12] = {
                31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
        };
        register int i;
        register long hms, day;
 
        day = tim / SECDAY;
        hms = tim % SECDAY;
 
        /* Hours, minutes, seconds are easy */
        tm->hour = hms / 3600;
        tm->min = (hms % 3600) / 60;
        tm->sec = (hms % 3600) % 60;
 
        /* Number of years in days */
        for (i = STARTOFTIME; day >= DAYS_IN_YEAR(i); i++)
                day -= DAYS_IN_YEAR(i);
        tm->year = i;
 
        /* Number of months in days left */
        if (LEAP_YEAR(tm->year))
                DAYS_IN_MONTH(FEBRUARY) = 29;
        for (i = 1; day >= DAYS_IN_MONTH(i); i++)
                day -= DAYS_IN_MONTH(i);
        DAYS_IN_MONTH(FEBRUARY) = 28;
        tm->mon = i;
 
        /* Days are what is left over (+1) from all that */
        tm->mday = day + 1;
 
        /* Determine the day of week */
        return rtc_calc_weekday(tm);
}
 
/*
 * Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 * => year=1980,  mon=12,  day=31,  hour=23,  min=59,  sec=59.
 *
 * [For the Julian calendar (which was used in Russia before 1917,
 * Britain & colonies before 1752,  anywhere else before 1582,
 * and is still in use by some communities) leave out the
 * -year / 100 + year / 400 terms,  and add 10.]
 *
 * This algorithm was first published by Gauss (I think).
 *
 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 * machines where long is 32-bit! (However, as time_t is signed, we
 * will already get problems at other places on 2038-01-19 03:14:08)
 */
unsigned long rtc_mktime(const struct rtc_time *tm)
{
        int mon = tm->mon;
        int year = tm->year;
        int days, hours;
 
        mon -= 2;
        if (0 >= (int)mon) {    /* 1..12 -> 11, 12, 1..10 */
                mon += 12;      /* Puts Feb last since it has leap day */
                year -= 1;
        }
 
        days = (unsigned long)(year / 4 - year / 100 + year / 400 +
                               367 * mon / 12 + tm->mday) +
                               year * 365 - 719499;
        hours = days * 24 + tm->hour;
        return (hours * 60 + tm->min) * 60 + tm->sec;
}
 
void rtc_display(const struct rtc_time *tm)
{
        printk(BIOS_INFO, "Date: %5d-%02d-%02d (%sday)  Time: %2d:%02d:%02d\n",
               tm->year,  tm->mon,  tm->mday,
               (tm->wday < 0 || tm->wday > 6) ? "unknown " : weekdays[tm->wday],
               tm->hour,  tm->min,  tm->sec);
}
 
static int rtc_month_days(unsigned int month, unsigned int year)
{
        int month_days[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
 
        return month_days[month] + (LEAP_YEAR(year) && month == 2);
}
 
int rtc_invalid(const struct rtc_time *tm)
{
        if (tm->sec > 59 || tm->min > 59 || tm->hour > 23 || tm->mon == 0 || tm->mon > 12 ||
            tm->year < 1970 || tm->mday > rtc_month_days(tm->mon - 1, tm->year))
                return 1;
        else
                return 0;
}