24 Numerics library [numerics]

24.7 Random number generation [rand]

24.7.2 Requirements [rand.req]

24.7.2.3 Uniform random bit generator requirements [rand.req.urng]

A uniform random bit generator g 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.

[ Note

The degree to which g's results approximate the ideal is often determined statistically.

— end note

]

template<class G>
  concept UniformRandomBitGenerator =
    Invocable<G&> && UnsignedIntegral<invoke_result_t<G&>> &&
    requires {
      G::min(); requires Same<decltype(G::min()), invoke_result_t<G&>>;
      G::max(); requires Same<decltype(G::max()), invoke_result_t<G&>>;
    };

Let g be an object of type G.

G models UniformRandomBitGenerator only if

(2.1)
both G::min() and G::max() are constant expressions ([expr.const]),
(2.2)
G::min() < G::max(),
(2.3)
G::min() <= g(),
(2.4)
g() <= G::max(), and
(2.5)
g() has amortized constant complexity.

A class G meets the uniform random bit generator requirements if G models UniformRandomBitGenerator, invoke_result_t<G&> is an unsigned integer type ([basic.fundamental]), and G provides a nested typedef-name result_type that denotes the same type as invoke_result_t<G&>.