--- /dev/null
+/* This file is taken from http://www.genealogy.org/~scottlee/
+ Only this initial comment has been added. The next comment
+ gives the original copyright notice.
+*/
+
+
+/* $selId: gregor.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
+ * SdnToGregorian(
+ * long int sdn,
+ * int *pYear,
+ * int *pMonth,
+ * int *pDay);
+ *
+ * Convert a SDN to a Gregorian calendar date. If the input SDN is less
+ * than 1, the three output values will all be set to zero, otherwise
+ * *pYear will be >= -4714 and != 0; *pMonth will be in the range 1 to 12
+ * inclusive; *pDay will be in the range 1 to 31 inclusive.
+ *
+ * long int
+ * GregorianToSdn(
+ * int inputYear,
+ * int inputMonth,
+ * int inputDay);
+ *
+ * Convert a Gregorian 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.
+ *
+ * char *MonthNameShort[13];
+ *
+ * Convert a Gregorian month number (1 to 12) to the abbreviated (three
+ * character) name of the Gregorian month (null terminated). An index of
+ * zero will return a zero length string.
+ *
+ * char *MonthNameLong[13];
+ *
+ * Convert a Gregorian month number (1 to 12) to the name of the Gregorian
+ * month (null terminated). An index of zero will return a zero length
+ * string.
+ *
+ * VALID RANGE
+ *
+ * 4714 B.C. to at least 10000 A.D.
+ *
+ * Although this software can handle dates all the way back to 4714
+ * B.C., such use may not be meaningful. The Gregorian calendar was
+ * not instituted until October 15, 1582 (or October 5, 1582 in the
+ * Julian calendar). Some countries did not accept it until much
+ * later. For example, Britain converted in 1752, The USSR in 1918 and
+ * Greece in 1923. Most European countries used the Julian calendar
+ * prior to the Gregorian.
+ *
+ * CALENDAR OVERVIEW
+ *
+ * The Gregorian calendar is a modified version of the Julian calendar.
+ * The only difference being the specification of leap years. The
+ * Julian calendar specifies that every year that is a multiple of 4
+ * will be a leap year. This leads to a year that is 365.25 days long,
+ * but the current accepted value for the tropical year is 365.242199
+ * days.
+ *
+ * To correct this error in the length of the year and to bring the
+ * vernal equinox back to March 21, Pope Gregory XIII issued a papal
+ * bull declaring that Thursday October 4, 1582 would be followed by
+ * Friday October 15, 1582 and that centennial years would only be a
+ * leap year if they were a multiple of 400. This shortened the year
+ * by 3 days per 400 years, giving a year of 365.2425 days.
+ *
+ * Another recently proposed change in the leap year rule is to make
+ * years that are multiples of 4000 not a leap year, but this has never
+ * been officially accepted and this rule is not implemented in these
+ * algorithms.
+ *
+ * ALGORITHMS
+ *
+ * The calculations are based on three different cycles: a 400 year
+ * cycle of leap years, 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 4714 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).
+ *
+ **************************************************************************/
+
+#include "sdncal.h"
+
+#define SDN_OFFSET 32045
+#define DAYS_PER_5_MONTHS 153
+#define DAYS_PER_4_YEARS 1461
+#define DAYS_PER_400_YEARS 146097
+
+void
+SdnToGregorian(
+ long int sdn,
+ int *pYear,
+ int *pMonth,
+ int *pDay)
+{
+ int century;
+ 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 century (year/100). */
+ century = temp / DAYS_PER_400_YEARS;
+
+ /* Calculate the year and day of year (1 <= dayOfYear <= 366). */
+ temp = ((temp % DAYS_PER_400_YEARS) / 4) * 4 + 3;
+ year = (century * 100) + (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
+GregorianToSdn(
+ int inputYear,
+ int inputMonth,
+ int inputDay)
+{
+ int year;
+ int month;
+
+ /* check for invalid dates */
+ if (inputYear == 0 || inputYear < -4714 ||
+ inputMonth <= 0 || inputMonth > 12 ||
+ inputDay <= 0 || inputDay > 31)
+ {
+ return(0);
+ }
+
+ /* check for dates before SDN 1 (Nov 25, 4714 B.C.) */
+ if (inputYear == -4714) {
+ if (inputMonth < 11) {
+ return(0);
+ }
+ if (inputMonth == 11 && inputDay < 25) {
+ 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 / 100) * DAYS_PER_400_YEARS) / 4
+ + ((year % 100) * DAYS_PER_4_YEARS) / 4
+ + (month * DAYS_PER_5_MONTHS + 2) / 5
+ + inputDay
+ - SDN_OFFSET );
+}
+
+char *MonthNameShort[13] = {
+ "",
+ "Jan",
+ "Feb",
+ "Mar",
+ "Apr",
+ "May",
+ "Jun",
+ "Jul",
+ "Aug",
+ "Sep",
+ "Oct",
+ "Nov",
+ "Dec"
+};
+
+char *MonthNameLong[13] = {
+ "",
+ "January",
+ "February",
+ "March",
+ "April",
+ "May",
+ "June",
+ "July",
+ "August",
+ "September",
+ "October",
+ "November",
+ "December"
+};
projects / gedcom-parse.git / blobdiff