if i am not mistaken now the program must check every provice from the depot
to the unit for the best route and it must do it again and again and again. this
uses alot of calculations that would not be needed as the supply "tree trunk" would come from the main depot to a supply front and then to the units (being
much closer and easier for the program to calculate) or alternativly thru the HQ
hierarchy to the front line units again with an easier calculation.
I suspect that you are mistaken.
As I understand it units don't actually trace supply at all - what they actually do is create demand in their province, this in turn creates demand in the "upstream" provinces, ultimately reaching the depot. Supply is then moved to satisfy that demand. There is no searching for the best route - the route just appears out of the order the provinces are processed in - furtherest from depot first.