BitArray: count the number of bits set

[yawniek via Digitalmars-d-learn]

i figured i can count the number of bits set for a BitArray with 
std.algorithm : count:

BitArray([0,0,1]).bitsSet.count()

but this seems not very optimal, is there a faster way directly 
accessible trough phobos?

ideally something that is optimized by the compiler.