Defined in header
template <class G>
concept uniform_random_bit_generator =
uniform_random_bit_generator<G> specifies that
G is the type of a uniform random bit generator, that is, objects of type
G is a function object returning unsigned integer values such that each value in the range of possible results has (ideally) equal probability of being returned.
 Semantic requirements
uniform_random_bit_generator<G> is modeled only if, given any object
g of type
g()is in the range
g()has amortized constant complexity.