Consistency question

Hi,

I am in the process of rewriting the core logic of git blame (the current speed of which is quite an impediment to some workflows). I currently have one question I don't see an answer to right away, and that question arises in doing a reasonably robust traversal of commits without determining topology first:

The question is what guarantees I have with regard to the commit date of a commit in relation to that of its parent commits:

a) none b) commitdate(child) >= commitdate(parent) c) commitdate(child) > commitdate(parent)

Obviously, I can rely on c) being true "almost always": it's definitely good for a heuristic used for improving performance (meaning as an ordering criterion for a commit priority queue). The problem is how much I should cater for graceful behavior for the cases where it's not.

Does git do any actual checks before pushing?