What is the use case of RandomCover?

[Ivan Kazmenko]

> 1. Speed.
> +randomShuffle performs O(n) steps and O(n) uniform() calls.
> -randomCover performs O(n^2) steps and O(n^2) uniform() calls.
>
> The latter however can (and perhaps should?) be optimized to 
> O(n): in the implementation, the line

Sorry, this part doesn't look clear.  O(n^2) total with O(n^2) 
uniform() calls can be optimized to the same O(n^2) total but 
with only O(n) uniform() calls.  It can be further optimized to 
O(n log n) total with O(n) uniform() calls using a Fenwick tree, 
but will then require storing n ints instead of n bools.