Out-of-bounds read in `Log2Cache::nlog2n()`, `nlog2n_difference()` and `plog2p()`

Log2Cache::newn fills its three tables with entries for 0..=n, but the three accessor methods index those tables with getunchecked on a value the caller supplies. Nothing bounds the argument and nothing documents a bound, so any value above the n the cache was built with reads past the end of the...