unitconvert: round to nearest date when converting to yyyymmdd.

This resolves an issue where converting from a low-precision decimalyear
to yyyymmdd gave the wrong result, due to mjd_to_yyyymmdd() truncating
away the fractional time component.

This commit changes the behaviour of mjd_to_yyyymmdd() to round to the
nearest date, instead of truncating.

Refs #1483

1 files changed, 7 insertions, 6 deletions

diff --git a/src/conversions/unitconvert.cpp b/src/conversions/unitconvert.cpp
index d584d93f..5a5042f0 100644
--- a/src/conversions/unitconvert.cpp
+++ b/src/conversions/unitconvert.cpp
@@ -252,21 +252,22 @@ static double yyyymmdd_to_mjd(double yyyymmdd) {
 /***********************************************************************/
 static double mjd_to_yyyymmdd(double mjd) {
 /************************************************************************
-    Date given in YYYY-MM-DD format.
+    Date returned in YYYY-MM-DD format.
 ************************************************************************/
-    double mjd_iter = 14 + 31;
-    int year = 1859, month=0, day=0;
+    unsigned int mjd_iter = 14 + 31;
+    unsigned int year = 1859, month = 0, day = 0;
+    unsigned int date = (int) lround(mjd);
 
-    for (; mjd >= mjd_iter; year++) {
+    for (; date >= mjd_iter; year++) {
         mjd_iter += days_in_year(year);
     }
     year--;
     mjd_iter -= days_in_year(year);
 
-    for (month=1; mjd_iter + days_in_month(year, month) <= mjd; month++)
+    for (month=1; mjd_iter + days_in_month(year, month) <= date; month++)
         mjd_iter += days_in_month(year, month);
 
-    day = (int)(mjd - mjd_iter + 1);
+    day = date - mjd_iter + 1;
 
     return year*10000.0 + month*100.0 + day;
 }