Mathematical principles of BRepExtrema_DistShapeShape？

[ＬＪＫ]

In OCC, BRepExtrema_DistShapeShape is used to calculate the shortest distance between two geometries. How is this shortest distance calculated?

 

[Quaoar]

I'm afraid the most accurate answer here would be diving into the code with a debugger and tracing down the execution flow branch after branch. This tool is full of specific case treatments and has had quite a long journey until it reached its current state.