Fix JDToGregorian(), which was broken for dates prior to 4713 BC; I

think it was due to use of int() when floor() was needed.

New JDToGregorian() is based on pseudocode by Peter Baum at this
website:  http://vsg.cape.com/~pbaum/date/injdimp.htm

CCMAIL: djarvie@astrojar.co.uk
CCMAIL: kstars-devel@kde.org

svn path=/trunk/KDE/kdeedu/libkdeedu/; revision=514973

diff --git a/extdate/extdatetime.cpp b/extdate/extdatetime.cpp
index f7c6d2f8b09ac911008c2387206caf45cf5134e9..7dccf40aa34970839815affadb299c8c637b463d 100644 (file)
--- a/extdate/extdatetime.cpp
+++ b/extdate/extdatetime.cpp
@@ -22,6 +22,7 @@
 #include <qstringlist.h>
 #include <assert.h>
 #include <time.h>
+#include <math.h>
 
 static const uint SECS_PER_DAY  = 86400;
 static const uint MSECS_PER_DAY = 86400000;
@@ -124,24 +125,30 @@ long int ExtDate::GregorianToJD( int year, int month, int day )
        return jd;
 }
 
+//JD to Gregorian code is based on an algorithm by Peter Baum, 
+//published here:  http://vsg.cape.com/~pbaum/date/injdimp.htm
 void   ExtDate::JDToGregorian( long int jd, int &year, int &month, int &day )
 {
-       int a, b, c, d, e, alpha;
+       float g;
+       int z, a, b, c;
+       
+       z = jd - 1721118;
+       g = z - 0.25;
 
-       if (jd<2299161) {
-               a = jd;
-       } else {
-               alpha = int ((jd-1867216.25)/ 36524.25);
-               a = jd + 1 + alpha - int(alpha / 4.0);
+       a = int(floor( g / 36524.25 ));
+       b = a - int(floor(a/4));
+
+       year = int(floor((b+g)/365.25));
+
+       c = b + z - int(floor(365.25*year));
+
+       month = int( ( 5*c + 456) / 153 );
+       day = c - int( ( 153*month - 457)/5);
+
+       if ( month > 12 ) {
+               year++;
+               month -= 12;
        }
-       b = a + 1524;
-       c = int ((b-122.1)/ 365.25);
-       d = int (365.25*c);
-       e = int ((b-d)/ 30.6001);
-
-       day = b-d-int(30.6001*e);
-       month = (e<14) ? e-1 : e-13;
-       year  = (month>2)  ? c-4716 : c-4715;
 }
 
 bool ExtDate::isValid() const