* implement AddMonths(...) and AddYears(...) functions

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27255 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/shared/DateTime.h

@@ -50,8 +50,10 @@ class BDate {
 
 		static BDate	CurrentDate(time_type type);
 		bool			SetDate(int32 year, int32 month, int32 day);
-		
+
 		void			AddDays(int32 days);
+		void			AddYears(int32 years);
+		void			AddMonths(int32 months);
 
 		int32			Day() const;
 		int32			Year() const;

src/kits/shared/DateTime.cpp

@@ -202,6 +202,47 @@ BDate::AddDays(int32 days)
 }
 
 
+void
+BDate::AddYears(int32 years)
+{
+	fYear += years;
+	fDay = min_c(fDay, DaysInMonth());
+}
+
+
+void
+BDate::AddMonths(int32 months)
+{
+	if (months == 0)
+		return;
+
+	if (months > 0) {
+		while (months > 0) {
+			fYear++;
+			months -= 12;
+		}
+
+		fMonth += months;
+		if (fMonth < 1) {
+			fYear--;
+			fMonth += 12;
+		}
+	} else {
+		while (months < 0) {
+			fYear--;
+			months += 12;
+		}
+
+		fMonth += months;
+		if (fMonth > 12) {
+			fYear++;
+			fMonth -= 12;
+		}
+	}
+	fDay = min_c(fDay, DaysInMonth());
+}
+
+
 int32
 BDate::Day() const
 {