IOS algorithm behind constraint & Auto Layout

Question

i'm trying to reverse engineer the layoutSubviews function in IOS where it calculates the autosizes and contraints. Normally, if we create constraints in orders: A depends (constrained) B, B depends C, and C was inited with a fix frame, a system should need to be smart enough to realise the calculation in order: C -> B -> A to avoid unneeded loops.

My question is: How does IOS (or what is the algorithm) traverse the list of NSLayoutContraint and calculate the frame in such order?

Answer 1

Just answering in case anyone needs it: IOS use Cassowary toolkit to do auto layout (http://www.cs.washington.edu/research/constraints/cassowary/)