u-boot/drivers/rtc/date.c

/*
 * (C) Copyright 2001
 * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
 *
 * SPDX-License-Identifier:	GPL-2.0+
 */

/*
 * Date & Time support for Philips PCF8563 RTC
 */

#include <common.h>
#include <command.h>
#include <errno.h>
#include <rtc.h>

#if defined(CONFIG_CMD_DATE) || defined(CONFIG_TIMESTAMP)

#define FEBRUARY		2
#define	STARTOFTIME		1970
#define SECDAY			86400L
#define SECYR			(SECDAY * 365)
#define	leapyear(year)		((year) % 4 == 0)
#define	days_in_year(a)		(leapyear(a) ? 366 : 365)
#define	days_in_month(a)	(month_days[(a) - 1])

static int month_days[12] = {
	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};

/*
 * This only works for the Gregorian calendar - i.e. after 1752 (in the UK)
 */
int rtc_calc_weekday(struct rtc_time *tm)
{
	int leapsToDate;
	int lastYear;
	int day;
	int MonthOffset[] = { 0,31,59,90,120,151,181,212,243,273,304,334 };

	if (tm->tm_year < 1753)
		return -EINVAL;
	lastYear=tm->tm_year-1;

	/*
	 * Number of leap corrections to apply up to end of last year
	 */
	leapsToDate = lastYear/4 - lastYear/100 + lastYear/400;

	/*
	 * This year is a leap year if it is divisible by 4 except when it is
	 * divisible by 100 unless it is divisible by 400
	 *
	 * e.g. 1904 was a leap year, 1900 was not, 1996 is, and 2000 will be
	 */
	if((tm->tm_year%4==0) &&
	   ((tm->tm_year%100!=0) || (tm->tm_year%400==0)) &&
	   (tm->tm_mon>2)) {
		/*
		 * We are past Feb. 29 in a leap year
		 */
		day=1;
	} else {
		day=0;
	}

	day += lastYear*365 + leapsToDate + MonthOffset[tm->tm_mon-1] + tm->tm_mday;

	tm->tm_wday=day%7;

	return 0;
}

void to_tm(int tim, struct rtc_time * tm)
{
	register int    i;
	register long   hms, day;

	day = tim / SECDAY;
	hms = tim % SECDAY;

	/* Hours, minutes, seconds are easy */
	tm->tm_hour = hms / 3600;
	tm->tm_min = (hms % 3600) / 60;
	tm->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->tm_year = i;

	/* Number of months in days left */
	if (leapyear(tm->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->tm_mon = i;

	/* Days are what is left over (+1) from all that. */
	tm->tm_mday = day + 1;

	/*
	 * Determine the day of week
	 */
	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 were 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
mktime (unsigned int year, unsigned int mon,
	unsigned int day, unsigned int hour,
	unsigned int min, unsigned int sec)
{
	if (0 >= (int) (mon -= 2)) {	/* 1..12 -> 11,12,1..10 */
		mon += 12;		/* Puts Feb last since it has leap day */
		year -= 1;
	}

	return (((
		(unsigned long) (year/4 - year/100 + year/400 + 367*mon/12 + day) +
			year*365 - 719499
	    )*24 + hour /* now have hours */
	  )*60 + min /* now have minutes */
	)*60 + sec; /* finally seconds */
}

#endif