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NAME

SYNOPSIS

#include <librock/sdncalh.h>

void
SdnToFrench(
        long int  sdn,
        int      *pYear,
        int      *pMonth,
        int      *pDay);
 /*
 * Convert a SDN to a French republican calendar date.  If the input SDN is
 * before the first day of year 1 or after the last day of year 14, the
 * three output values will all be set to zero, otherwise *pYear will be in
 * the range 1 to 14 inclusive; *pMonth will be in the range 1 to 13
 * inclusive; *pDay will be in the range 1 to 30 inclusive.  If *pMonth is
 * 13, the SDN represents one of the holidays at the end of the year and
 * *pDay will be in the range 1 to 6 inclusive.
 */
long int
librock_FrenchToSdn(
          int year,
          int month,
          int day);
 /*
 * Convert a French republican 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 *librock_FrenchMonthName[14];
 /*
 * Convert a French republican month number (1 to 13) to the name of the
 * French republican month (null terminated).  An index of 13 (for the
 * "extra" days at the end of the year) will return the string "Extra".  An
 * index of zero will return a zero length string.
 */

DESCRIPTION

 /* 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.
 *
 * 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 ...
         }
     }

VALID RANGE

 /*
 *     These routines only convert dates in years 1 through 14 (Gregorian
 *     dates 22 September 1792 through 22 September 1806).  This more than
 *     covers the period when the calendar was in use.
 *
 *     I would support a wider range of dates, but I have not been able to
 *     find an authoritative definition of when leap years were to have
 *     occurred.  There are suggestions that it was to skip a leap year ever
 *     100 years like the Gregorian calendar.
 */

CALENDAR OVERVIEW

 /*
 *     The French republican calendar was adopted in October 1793 during
 *     the French Revolution and was abandoned in January 1806.  The intent
 *     was to create a new calendar system that was based on scientific
 *     principals, not religious traditions.
 *
 *     The year is divided into 12 months of 30 days each.  The remaining 5
 *     to 6 days in the year are grouped at the end and are holidays.  Each
 *     month is divided into three decades (instead of weeks) of 10 days
 *     each.
 *
 *     The epoch (first day of the first year) is 22 September 1792 in the
 *     Gregorian calendar.  Leap years are every fourth year (year 3, 7,
 *     11, etc.)
 */

TESTING

 /*
 *     This algorithm has been tested from the year 1 to 14.  The source
 *     code of the verification program is included in the sdncal package.
 */

REFERENCES

 /*
 *     I have found no detailed, authoritative reference on this calendar.
 *     The algorithms are based on a preponderance of less authoritative
 *     sources.
 */

USES

  //No external calls

LICENSE

  Copyright 1993-1995, Scott E. Lee, all rights reserved.
  Licensed under BSD-ish license, NO WARRANTY. Copies must retain this block.
  License text in <librock/license/sdncal.txt> librock_LIDESC_HC=553e181388455f0eef17ccd9e2a51c1f3ae8daf0

Source Code

This software is part of Librock

• Source code which is Open-source, Free (Libre) and free (no cost)
• Namespace limited. All compile-time macros and names visible at link time are prefixed by "librock_". Integrate into your project and expect no name collisions.
• Stable API means new functions get new names so that there is no risk that updating a source file will break existing applications.
• Highly portable, cross-platform, and multithread compatible. Works with many machines, compilers, and operating systems (gcc/MSVC/Windows/Linux/BSD).

Verbatim copying and distribution of this generated page is permitted in any medium provided that no changes are made.
(The source of this manual page may be covered by a more permissive license which allows modifications.)

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