An awakened animal gets 3d6 Intelligence, +1d3 Charisma, and +2 HD. Its type becomes magical beast (augmented animal). An awakened animal can’t serve as an animal companion, familiar, or special mount.
Now, lets say we take the standard house cat from SRD, it has a HD of 1/2d8. Does the +2HD give +2 of the cat's HD (for a total of 1 and a 1/2HD)? Or does it just give a standard +2 (for a total of 2 1/2 HD)?
In both examples, do you round down or up for the purpose of ECL?
In the former example, if you did round down, would that allow a potential PC to swap out the first racial hit die for a class hit die, effectively creating an ECL 1 character?