mirror of
https://github.com/php/php-src.git
synced 2024-09-22 10:27:25 +00:00
241 lines
7.6 KiB
C
241 lines
7.6 KiB
C
/* $selId: julian.c,v 2.0 1995/10/24 01:13:06 lees Exp $
|
|
* Copyright 1993-1995, Scott E. Lee, all rights reserved.
|
|
* Permission granted to use, copy, modify, distribute and sell so long as
|
|
* the above copyright and this permission statement are retained in all
|
|
* copies. THERE IS NO WARRANTY - USE AT YOUR OWN RISK.
|
|
*/
|
|
|
|
/**************************************************************************
|
|
*
|
|
* These are the externally visible components of this file:
|
|
*
|
|
* void
|
|
* SdnToJulian(
|
|
* long int sdn,
|
|
* int *pYear,
|
|
* int *pMonth,
|
|
* int *pDay);
|
|
*
|
|
* Convert a SDN to a Julian calendar date. If the input SDN is less than
|
|
* 1, the three output values will all be set to zero, otherwise *pYear
|
|
* will be >= -4713 and != 0; *pMonth will be in the range 1 to 12
|
|
* inclusive; *pDay will be in the range 1 to 31 inclusive.
|
|
*
|
|
* long int
|
|
* JulianToSdn(
|
|
* int inputYear,
|
|
* int inputMonth,
|
|
* int inputDay);
|
|
*
|
|
* Convert a Julian calendar date to a SDN. Zero is returned when the
|
|
* input date is detected as invalid or out of the supported range. The
|
|
* return value will be > 0 for all valid, supported dates, but there are
|
|
* some invalid dates that will return a positive value. To verify that a
|
|
* date is valid, convert it to SDN and then back and compare with the
|
|
* original.
|
|
*
|
|
* VALID RANGE
|
|
*
|
|
* 4713 B.C. to at least 10000 A.D.
|
|
*
|
|
* Although this software can handle dates all the way back to 4713
|
|
* B.C., such use may not be meaningful. The calendar was created in
|
|
* 46 B.C., but the details did not stabilize until at least 8 A.D.,
|
|
* and perhaps as late at the 4th century. Also, the beginning of a
|
|
* year varied from one culture to another - not all accepted January
|
|
* as the first month.
|
|
*
|
|
* CALENDAR OVERVIEW
|
|
*
|
|
* Julias Ceasar created the calendar in 46 B.C. as a modified form of
|
|
* the old Roman republican calendar which was based on lunar cycles.
|
|
* The new Julian calendar set fixed lengths for the months, abandoning
|
|
* the lunar cycle. It also specified that there would be exactly 12
|
|
* months per year and 365.25 days per year with every 4th year being a
|
|
* leap year.
|
|
*
|
|
* Note that the current accepted value for the tropical year is
|
|
* 365.242199 days, not 365.25. This lead to an 11 day shift in the
|
|
* calendar with respect to the seasons by the 16th century when the
|
|
* Gregorian calendar was created to replace the Julian calendar.
|
|
*
|
|
* The difference between the Julian and today's Gregorian calendar is
|
|
* that the Gregorian does not make centennial years leap years unless
|
|
* they are a multiple of 400, which leads to a year of 365.2425 days.
|
|
* In other words, in the Gregorian calendar, 1700, 1800 and 1900 are
|
|
* not leap years, but 2000 is. All centennial years are leap years in
|
|
* the Julian calendar.
|
|
*
|
|
* The details are unknown, but the lengths of the months were adjusted
|
|
* until they finally stablized in 8 A.D. with their current lengths:
|
|
*
|
|
* January 31
|
|
* February 28/29
|
|
* March 31
|
|
* April 30
|
|
* May 31
|
|
* June 30
|
|
* Quintilis/July 31
|
|
* Sextilis/August 31
|
|
* September 30
|
|
* October 31
|
|
* November 30
|
|
* December 31
|
|
*
|
|
* In the early days of the calendar, the days of the month were not
|
|
* numbered as we do today. The numbers ran backwards (decreasing) and
|
|
* were counted from the Ides (15th of the month - which in the old
|
|
* Roman republican lunar calendar would have been the full moon) or
|
|
* from the Nonae (9th day before the Ides) or from the beginning of
|
|
* the next month.
|
|
*
|
|
* In the early years, the beginning of the year varied, sometimes
|
|
* based on the ascension of rulers. It was not always the first of
|
|
* January.
|
|
*
|
|
* Also, today's epoch, 1 A.D. or the birth of Jesus Christ, did not
|
|
* come into use until several centuries later when Christianity became
|
|
* a dominant religion.
|
|
*
|
|
* ALGORITHMS
|
|
*
|
|
* The calculations are based on two different cycles: a 4 year cycle
|
|
* of leap years and a 5 month cycle of month lengths.
|
|
*
|
|
* The 5 month cycle is used to account for the varying lengths of
|
|
* months. You will notice that the lengths alternate between 30 and
|
|
* 31 days, except for three anomalies: both July and August have 31
|
|
* days, both December and January have 31, and February is less than
|
|
* 30. Starting with March, the lengths are in a cycle of 5 months
|
|
* (31, 30, 31, 30, 31):
|
|
*
|
|
* Mar 31 days \
|
|
* Apr 30 days |
|
|
* May 31 days > First cycle
|
|
* Jun 30 days |
|
|
* Jul 31 days /
|
|
*
|
|
* Aug 31 days \
|
|
* Sep 30 days |
|
|
* Oct 31 days > Second cycle
|
|
* Nov 30 days |
|
|
* Dec 31 days /
|
|
*
|
|
* Jan 31 days \
|
|
* Feb 28/9 days |
|
|
* > Third cycle (incomplete)
|
|
*
|
|
* For this reason the calculations (internally) assume that the year
|
|
* starts with March 1.
|
|
*
|
|
* TESTING
|
|
*
|
|
* This algorithm has been tested from the year 4713 B.C. to 10000 A.D.
|
|
* The source code of the verification program is included in this
|
|
* package.
|
|
*
|
|
* REFERENCES
|
|
*
|
|
* Conversions Between Calendar Date and Julian Day Number by Robert J.
|
|
* Tantzen, Communications of the Association for Computing Machinery
|
|
* August 1963. (Also published in Collected Algorithms from CACM,
|
|
* algorithm number 199). [Note: the published algorithm is for the
|
|
* Gregorian calendar, but was adjusted to use the Julian calendar's
|
|
* simpler leap year rule.]
|
|
*
|
|
**************************************************************************/
|
|
|
|
#include "sdncal.h"
|
|
|
|
#define SDN_OFFSET 32083
|
|
#define DAYS_PER_5_MONTHS 153
|
|
#define DAYS_PER_4_YEARS 1461
|
|
|
|
void SdnToJulian(
|
|
long int sdn,
|
|
int *pYear,
|
|
int *pMonth,
|
|
int *pDay)
|
|
{
|
|
int year;
|
|
int month;
|
|
int day;
|
|
long int temp;
|
|
int dayOfYear;
|
|
|
|
if (sdn <= 0) {
|
|
*pYear = 0;
|
|
*pMonth = 0;
|
|
*pDay = 0;
|
|
return;
|
|
}
|
|
temp = (sdn + SDN_OFFSET) * 4 - 1;
|
|
|
|
/* Calculate the year and day of year (1 <= dayOfYear <= 366). */
|
|
year = temp / DAYS_PER_4_YEARS;
|
|
dayOfYear = (temp % DAYS_PER_4_YEARS) / 4 + 1;
|
|
|
|
/* Calculate the month and day of month. */
|
|
temp = dayOfYear * 5 - 3;
|
|
month = temp / DAYS_PER_5_MONTHS;
|
|
day = (temp % DAYS_PER_5_MONTHS) / 5 + 1;
|
|
|
|
/* Convert to the normal beginning of the year. */
|
|
if (month < 10) {
|
|
month += 3;
|
|
} else {
|
|
year += 1;
|
|
month -= 9;
|
|
}
|
|
|
|
/* Adjust to the B.C./A.D. type numbering. */
|
|
year -= 4800;
|
|
if (year <= 0)
|
|
year--;
|
|
|
|
*pYear = year;
|
|
*pMonth = month;
|
|
*pDay = day;
|
|
}
|
|
|
|
long int JulianToSdn(
|
|
int inputYear,
|
|
int inputMonth,
|
|
int inputDay)
|
|
{
|
|
int year;
|
|
int month;
|
|
|
|
/* check for invalid dates */
|
|
if (inputYear == 0 || inputYear < -4713 ||
|
|
inputMonth <= 0 || inputMonth > 12 ||
|
|
inputDay <= 0 || inputDay > 31) {
|
|
return (0);
|
|
}
|
|
/* check for dates before SDN 1 (Jan 2, 4713 B.C.) */
|
|
if (inputYear == -4713) {
|
|
if (inputMonth == 1 && inputDay == 1) {
|
|
return (0);
|
|
}
|
|
}
|
|
/* Make year always a positive number. */
|
|
if (inputYear < 0) {
|
|
year = inputYear + 4801;
|
|
} else {
|
|
year = inputYear + 4800;
|
|
}
|
|
|
|
/* Adjust the start of the year. */
|
|
if (inputMonth > 2) {
|
|
month = inputMonth - 3;
|
|
} else {
|
|
month = inputMonth + 9;
|
|
year--;
|
|
}
|
|
|
|
return ((year * DAYS_PER_4_YEARS) / 4
|
|
+ (month * DAYS_PER_5_MONTHS + 2) / 5
|
|
+ inputDay
|
|
- SDN_OFFSET);
|
|
}
|