Using % vs comparison and reset was probably more efficient with the compilers of the time; might still be.

Also I doubt everyone would agree that the one exit condition is more clear. For example, if I know that if e->inuse is 0 it will continue with the next round. Arguably it's more difficult to understand that from the single combined expression—because it isn't so: if !e->inuse but e == ent->client->chase_target, the original will loop but yours will exit.

Though I'm guessing ent->client->chase_target->inuse is probably never 0.