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swe/src/swepdate.c
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swe/src/swepdate.c
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/*****************************************************
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$Header: swepdate.c,v 1.65 2003/06/14 13:02:01 alois Exp $
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Placalc compatibility interface for Swiss Ephemeris.
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date functions
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*******************************************************/
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/* Copyright (C) 1997 - 2008 Astrodienst AG, Switzerland. All rights reserved.
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License conditions
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------------------
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This file is part of Swiss Ephemeris.
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Swiss Ephemeris is distributed with NO WARRANTY OF ANY KIND. No author
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or distributor accepts any responsibility for the consequences of using it,
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or for whether it serves any particular purpose or works at all, unless he
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or she says so in writing.
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Swiss Ephemeris is made available by its authors under a dual licensing
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system. The software developer, who uses any part of Swiss Ephemeris
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in his or her software, must choose between one of the two license models,
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which are
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a) GNU public license version 2 or later
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b) Swiss Ephemeris Professional License
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The choice must be made before the software developer distributes software
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containing parts of Swiss Ephemeris to others, and before any public
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service using the developed software is activated.
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If the developer choses the GNU GPL software license, he or she must fulfill
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the conditions of that license, which includes the obligation to place his
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or her whole software project under the GNU GPL or a compatible license.
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See http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
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If the developer choses the Swiss Ephemeris Professional license,
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he must follow the instructions as found in http://www.astro.com/swisseph/
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and purchase the Swiss Ephemeris Professional Edition from Astrodienst
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and sign the corresponding license contract.
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The License grants you the right to use, copy, modify and redistribute
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Swiss Ephemeris, but only under certain conditions described in the License.
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Among other things, the License requires that the copyright notices and
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this notice be preserved on all copies.
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Authors of the Swiss Ephemeris: Dieter Koch and Alois Treindl
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The authors of Swiss Ephemeris have no control or influence over any of
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the derived works, i.e. over software or services created by other
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programmers which use Swiss Ephemeris functions.
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The names of the authors or of the copyright holder (Astrodienst) must not
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be used for promoting any software, product or service which uses or contains
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the Swiss Ephemeris. This copyright notice is the ONLY place where the
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names of the authors can legally appear, except in cases where they have
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given special permission in writing.
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The trademarks 'Swiss Ephemeris' and 'Swiss Ephemeris inside' may be used
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for promoting such software, products or services.
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*/
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/*
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* This file is part of the PLACALC compatibility interface for Swiss Ephemeris.
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* It allows very easy porting of older Placalc application to the SwissEph.
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* A user has to replace #include "placalc.h" and "housasp.h" with
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* #include "swepcalc.h"
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* If he has used "ourdef.h" he replaces it with "sweodef.h".
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* Then he links his application with swepcalc.o and runs it against the
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* Swiss Ephemeris DLL or linkable library.
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*
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* All calls which were present in the placalc sources are contained
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* here, and either implemented directly or translated into Swiss Ephemeris
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* calls.
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*
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*
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*/
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#include "swepcalc.h"
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#include "swephexp.h"
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/*************** julday ********************************************
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* This function returns the absolute Julian day number (JD)
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* for a given calendar date.
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* The arguments are a calendar date: day, month, year as integers,
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* hour as double with decimal fraction.
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* If gregflag = 1, Gregorian calendar is assumed, gregflag = 0
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* Julian calendar is assumed.
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*
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The Julian day number is system of numbering all days continously
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within the time range of known human history. It should be familiar
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for every astrological or astronomical programmer. The time variable
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in astronomical theories is usually expressed in Julian days or
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Julian centuries (36525 days per century) relative to some start day;
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the start day is called 'the epoch'.
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The Julian day number is a double representing the number of
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days since JD = 0.0 on 1 Jan -4712, 12:00 noon.
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Midnight has always a JD with fraction .5, because traditionally
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the astronomical day started at noon. This was practical because
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then there was no change of date during a night at the telescope.
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From this comes also the fact the noon ephemerides were printed
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before midnight ephemerides were introduced early in the 20th century.
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NOTE: The Julian day number is named after the monk Julianus. It must
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not be confused with the Julian calendar system, which is named after
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Julius Cesar, the Roman politician who introduced this calendar.
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The Julian century is named after Cesar, i.e. a century in the Julian
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calendar. The 'gregorian' century has a variable length.
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Be aware the we always use astronomical year numbering for the years
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before Christ, not the historical year numbering.
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Astronomical years are done with negative numbers, historical
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years with indicators BC or BCE (before common era).
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Year 0 (astronomical) = 1 BC
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year -1 (astronomical) = 2 BC
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etc.
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Original author: Marc Pottenger, Los Angeles.
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with bug fix for year < -4711 15-aug-88 by Alois Treindl
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(The parameter sequence m,d,y still indicates the US origin,
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be careful because the similar function date_conversion() uses
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other parameter sequence and also Astrodienst relative juldate.)
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References: Oliver Montenbruck, Grundlagen der Ephemeridenrechnung,
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Verlag Sterne und Weltraum (1987), p.49 ff
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related functions: revjul() reverse Julian day number: compute the
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calendar date from a given JD
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date_conversion() includes test for legal date values
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and notifies errors like 32 January.
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****************************************************************/
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double julday(int month, int day, int year, double hour, int gregflag)
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{
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double jd;
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jd = swe_julday(year, month, day, hour, gregflag);
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return jd;
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}
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/*
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* monday = 0, ... sunday = 6
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*/
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int day_of_week(double jd)
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{
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return (((int) floor (jd - 2433282 - 1.5) %7) + 7) % 7;
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}
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/*************** julday ******************
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get absolute julian day number (author: Marc Pottenger)
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with bug fix for year < -4711 15-aug-88
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*/
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double juldays(int gregflag, ADATE *adp )
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{
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return swe_julday(adp->year, adp->month, adp->day, adp->csec / 360000.0, gregflag);
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}
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/*** revjul ******************************************************
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revjul() is the inverse function to julday(), see the description
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there.
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Arguments are julian day number, calendar flag (0=julian, 1=gregorian)
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return values are the calendar day, month, year and the hour of
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the day with decimal fraction (0 .. 23.999999).
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Be aware the we use astronomical year numbering for the years
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before Christ, not the historical year numbering.
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Astronomical years are done with negative numbers, historical
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years with indicators BC or BCE (before common era).
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Year 0 (astronomical) = 1 BC historical year
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year -1 (astronomical) = 2 BC historical year
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year -234 (astronomical) = 235 BC historical year
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etc.
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Original author Mark Pottenger, Los Angeles.
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with bug fix for year < -4711 16-aug-88 Alois Treindl
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*************************************************************************/
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void revjul (double jd, int gregflag,
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int *jmon, int *jday, int *jyear, double *jut)
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{
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swe_revjul(jd, gregflag, jyear, jmon, jday, jut);
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}
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/************************************* revjul *********
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get calendar date from julian day #
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with bug fix for year < -4711 16-aug-88
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arguments are julian day #, calendar flag (0=julian, 1=gregorian)
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*/
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void revjuls(double jd, int gregflag, struct adate *adp)
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{
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double jut;
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swe_revjul(jd, gregflag, &adp->year, &adp->month, &adp->day, &jut);
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adp->csec = jut * 360000.0 + 0.5;
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}
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/*********************************************************
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$Header: swepdate.c,v 1.65 2003/06/14 13:02:01 alois Exp $
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version 15-feb-89 16:30
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This function converts some date+time input {d,m,y,utime}
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into the Julian day number tgmt, which is an Astrodienst relative
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Julian date.
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The function checks that the input is a legal combination
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of dates; for illegal dates like 32 January 1993 it returns ERR
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but still converts the date correctly, i.e. like 1 Feb 1993.
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The function is usually used to convert user input of birth data
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into the Julian day number. Illegal dates should be notified to the user.
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Be aware the we always use astronomical year numbering for the years
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before Christ, not the historical year numbering.
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Astronomical years are done with negative numbers, historical
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years with indicators BC or BCE (before common era).
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Year 0 (astronomical) = 1 BC historical.
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year -1 (astronomical) = 2 BC
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etc.
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Many users of Astro programs do not know about this difference.
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Return: OK or ERR (for illegal date)
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*********************************************************/
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int date_conversion (int d ,
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int m ,
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int y , /* day, month, year */
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centisec gutime, /* greenwich time in centiseconds */
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char c, /* calendar g[regorian]|j[ulian]|a[stro = greg] */
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double *tgmt
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/* julian date relative 0.Jan.1950 12:00 gmt */
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/* shift is 2433282 from absolute Julian date */
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)
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{
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int rday, rmon, ryear;
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double rut, jd;
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int gregflag = SE_JUL_CAL;
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if (c == 'g' || c == 'a')
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gregflag = SE_GREG_CAL;
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rut = gutime / 360000.0; /* hours GMT */
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jd = julday(m, d, y, rut, gregflag);
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revjul(jd, gregflag, &rmon, &rday, &ryear, &rut);
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*tgmt = jd - JUL_OFFSET;
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if (rmon == m && rday == d && ryear == y) {
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return OK;
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} else {
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return ERR;
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}
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} /* end date_conversion */
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