implement MLD shortest path plugin

src/engine/routing_algorithms/routing_base.cpp

@@ -0,0 +1,28 @@
+#include "engine/routing_algorithms/routing_base.hpp"
+
+namespace osrm
+{
+namespace engine
+{
+namespace routing_algorithms
+{
+
+bool needsLoopForward(const PhantomNode &source_phantom, const PhantomNode &target_phantom)
+{
+    return source_phantom.forward_segment_id.enabled && target_phantom.forward_segment_id.enabled &&
+           source_phantom.forward_segment_id.id == target_phantom.forward_segment_id.id &&
+           source_phantom.GetForwardWeightPlusOffset() >
+               target_phantom.GetForwardWeightPlusOffset();
+}
+
+bool needsLoopBackwards(const PhantomNode &source_phantom, const PhantomNode &target_phantom)
+{
+    return source_phantom.reverse_segment_id.enabled && target_phantom.reverse_segment_id.enabled &&
+           source_phantom.reverse_segment_id.id == target_phantom.reverse_segment_id.id &&
+           source_phantom.GetReverseWeightPlusOffset() >
+               target_phantom.GetReverseWeightPlusOffset();
+}
+
+} // namespace routing_algorithms
+} // namespace engine
+} // namespace osrm