expected number of elements in bucket set
ratio of n to the number of buckets. The desired (approximate) number of elements per bucket. For example, 0.5 sets the number of buckets to double n; for 2 the number of buckets is the half of n. load_factor must be greater than 0 (this is asserted in IBucketSet.calcNumBucketsExp2()). The load factor is basically a trade-off between memory usage (number of buckets) and search time (number of elements per bucket).
Constructor, uses the default implementation for the bucket element allocator: Elements are allocated by 'new' and stored in a free list.
Sets the number of buckets to n / load_factor, rounded up to the nearest power or 2.