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diff --git a/gedcom/calendar/sdncal.h b/gedcom/calendar/sdncal.h
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+/* 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.
+*/
+
+#ifndef _INCLUDED_SDNCAL_H
+#define _INCLUDED_SDNCAL_H
+
+/* $selId: sdncal.h,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.
+ */
+
+/**************************************************************************
+ *
+ * This package defines a set of routines that convert calendar dates to
+ * and from a serial day number (SDN).  The SDN is a serial numbering of
+ * days where SDN 1 is November 25, 4714 BC in the Gregorian calendar and
+ * SDN 2447893 is January 1, 1990.  This system of day numbering is
+ * sometimes referred to as Julian days, but to avoid confusion with the
+ * Julian calendar, it is referred to as serial day numbers here.  The term
+ * Julian days is also used to mean the number of days since the beginning
+ * of the current year.
+ *
+ * The SDN can be used as an intermediate step in converting from one
+ * calendar system to another (such as Gregorian to Jewish).  It can also
+ * be used for date computations such as easily comparing two dates,
+ * determining the day of the week, finding the date of yesterday or
+ * calculating the number of days between two dates.
+ *
+ * When using this software on 16 bit systems, be careful to store SDNs in
+ * a long int, because it will not fit in the 16 bits that some systems
+ * allocate to an int.
+ *
+ * For each calendar, there are two routines provided.  One converts dates
+ * in that calendar to SDN and the other converts SDN to calendar dates.
+ * The routines are named SdnTo<CALENDAR>() and <CALENDAR>ToSdn(), where
+ * <CALENDAR> is the name of the calendar system.
+ *
+ * SDN values less than one are not supported.  If a conversion routine
+ * returns an SDN of zero, this means that the date given is either invalid
+ * or is outside the supported range for that calendar.
+ *
+ * At least some validity checks are performed on input dates.  For
+ * example, a negative month number will result in the return of zero for
+ * the SDN.  A returned SDN greater than one does not necessarily mean that
+ * the input date was valid.  To determine if the date is valid, convert it
+ * to SDN, and if the SDN is greater than zero, convert it back to a date
+ * and compare to the original.  For example:
+ *
+ *    int y1, m1, d1;
+ *    int y2, m2, d2;
+ *    long int sdn;
+ *    ...
+ *    sdn = GregorianToSdn(y1, m1, d1);
+ *    if (sdn > 0) {
+ *        SdnToGregorian(sdn, &y2, &m2, &d2);
+ *        if (y1 == y2 && m1 == m2 && d1 == d2) {
+ *            ... date is valid ...
+ *        }
+ *    }
+ *
+ **************************************************************************/
+
+/* Gregorian calendar conversions. */
+void SdnToGregorian(long int sdn, int *pYear, int *pMonth, int *pDay);
+long int GregorianToSdn(int year, int month, int day);
+extern char *MonthNameShort[13];
+extern char *MonthNameLong[13];
+
+/* Julian calendar conversions. */
+void SdnToJulian(long int sdn, int *pYear, int *pMonth, int *pDay);
+long int JulianToSdn(int year, int month, int day);
+
+/* Jewish calendar conversions. */
+void SdnToJewish(long int sdn, int *pYear, int *pMonth, int *pDay);
+long int JewishToSdn(int year, int month, int day);
+extern char *JewishMonthName[14];
+
+/* French republic calendar conversions. */
+void SdnToFrench(long int sdn, int *pYear, int *pMonth, int *pDay);
+long int FrenchToSdn(int inputYear, int inputMonth, int inputDay);
+extern char *FrenchMonthName[14];
+
+/* Islamic calendar conversions. */
+/* Not implemented yet. */
+
+/* Day of week conversion.  0=Sunday, 6=Saturday */
+int DayOfWeek(long int sdn);
+extern char *DayNameShort[7];
+extern char *DayNameLong[7];
+
+#endif /* _INCLUDED_SDNCAL_H */