OT: Zjisteni licheho/sudeho dne

[Karel Zak]

On Wed, 26 Jul 2000, Michal Krause wrote:

> Zdravim.
> 
> Omlouvam se za OT, ale nevite nekdo, jakym zpusobem spolehlive zjistit
> zda je den lichy nebo sudy (je jedno, jestli treba od roku 1970 nebo od
> jineho datumu).

 To, ale musis rict co je to sudy/lichy den :-) Tedy mysleno od ceho to
pocitas - od zacatku roku, mesice, pocatku vesmiru apod...

 To jak ti tu nekdo radil s julianskym kalendarem je opravdu asi 
nejlepsi. Tady to mas v C obousmernou konverzi:

/*
 * Calendar time to Julian date conversions.
 * Julian date is commonly used in astronomical applications,
 *	since it is numerically accurate and computationally simple.
 * The algorithms here will accurately convert between Julian day
 *	and calendar date for all non-negative Julian days
 *	(i.e. from Nov 23, -4713 on).
 *
 * Ref: Explanatory Supplement to the Astronomical Almanac, 1992.
 *	University Science Books, 20 Edgehill Rd. Mill Valley CA 94941.
 *
 * Use the algorithm by Henry Fliegel, a former NASA/JPL colleague
 *	now at Aerospace Corp. (hi, Henry!)
 *
 * These routines will be used by other date/time packages - tgl 97/02/25
 */

int
date2j(int y, int m, int d)
{
	int			m12 = (m - 14) / 12;

	return ((1461 * (y + 4800 + m12)) / 4 + (367 * (m - 2 - 12 * (m12))) / 12
			- (3 * ((y + 4900 + m12) / 100)) / 4 + d - 32075);
}	/* date2j() */

void
j2date(int jd, int *year, int *month, int *day)
{
	int			j,
				y,
				m,
				d;

	int			i,
				l,
				n;

	l = jd + 68569;
	n = (4 * l) / 146097;
	l -= (146097 * n + 3) / 4;
	i = (4000 * (l + 1)) / 1461001;
	l += 31 - (1461 * i) / 4;
	j = (80 * l) / 2447;
	d = l - (2447 * j) / 80;
	l = j / 11;
	m = (j + 2) - (12 * l);
	y = 100 * (n - 49) + i + l;

	*year = y;
	*month = m;
	*day = d;
	return;
}	/* j2date() */


---
 Snad se na tebe NASA & PostgreSQL nebude zlobit :-)
--- 
 Pouziti:
 ~~~~~~~

 int j = date2j(tm->tm_year, tm->tm_mon, tm->tm_mday);

 if ((((unsigned) j) | 1) == j)

	printf("Jsem lichej!")

 else
	printf("Jsem sudej!");


 ... welcome to date/time alchemy ...

					Karel