node_levels name introduces confusion

[rudazhang]

GraphContractor::node_levels represents levels of nodes in a contraction hierarchy, which is declared as a vector of float:
https://github.com/Project-OSRM/osrm-backend/blob/master/include/contractor/graph_contractor.hpp#L1111

But it is assigned as current_level:
https://github.com/Project-OSRM/osrm-backend/blob/master/include/contractor/graph_contractor.hpp#L468

which is unsigned.
https://github.com/Project-OSRM/osrm-backend/blob/master/include/contractor/graph_contractor.hpp#L324

[MoKob]

The assigned values and the chosen name might suggest so. We should probably consider using a different name?

We use these node_levels as a source of node_priorities which requires a swap here. This swap is only possible if both node_priorities and node_levels match in type.

Possible solutions I see for this kind of ugly type-situation:

• rename node_levels to something like node_priorities_from_levels
• do a transformation rather than a swap at the above location (slower, but a single vector might be fine)

Personally I'd prefer the second solution, since we do it once, only at the beginning of the contraction and copying the memory should only be a few seconds. The main drawback is that if you require frequent updates (which is kind of the reason for having this cache in the first place), we would end up adding additional timing in here.

In total, I'd say that renaming this could remove confusion and give a clearer intend on what it is used for.

[rudazhang]

Sorry I didn't realize the .level file is only intended to be used as node_priorities, instead of an exact cache of CH levels in the previous run.
And I agree renaming the variable (and probably the .level filename) would clear confusion.

[97littleleaf11]

It seems that the related code structure had changed a lot. Maybe this issue is out-of-date?