So the risk here is that by adding the floordiv fast path, the division code is duplicated, and that increases the risk of accidentally losing the invariant that `a // b` is interchangeable with `divmod(a, b)[0]` (e.g., because someone decides to "fix" the floor float division). That and the usual increased maintenance cost of more code.

Whether the optimization is worth the cost, I'm not sure. My gut feeling is not, but others may have different views.