added method to compute extensionIndex from reusedIndex and libraryIndex

fr.mem4csd.osatedim.viatra/src/fr/mem4csd/osatedim/viatra/utils/LibraryUtils.java

@@ -35,6 +35,20 @@ public class LibraryUtils {
 		return returnList;
 	}
 	
+	public static Integer getExtensionIndex(Integer libraryIndex, Integer reusedIndex, Boolean modifyReused) {
+		if (modifyReused) {
+			return libraryIndex;
+		} else {
+			if (libraryIndex == -1) {
+				return reusedIndex;
+			} else if (reusedIndex == -1) {
+				return libraryIndex;
+			} else {
+				return Math.min(reusedIndex, libraryIndex);
+			}
+		}
+	}
+	
 	public static EList<ComponentType> getAllInheritingParentTypes(Feature feat, ComponentInstance compinst) {
 		final EList<ComponentType> returnList = new BasicEList<ComponentType>();
 		ComponentType comptype;
@@ -189,7 +203,7 @@ public class LibraryUtils {
 		if (extensionType == sourceType) {
 			return true;
 		}
-		while (extensionType.getExtended() != null) {
+		while (extensionType != null) {
 			if (extensionType == sourceType) {
 				return true;
 			} else {