# 26 Numerics library [numerics]

## 26.5 Random number generation [rand]

### 26.5.1 Requirements [rand.req]

#### 26.5.1.5 Random number engine adaptor requirements [rand.req.adapt]

A random number engine adaptor (commonly shortened to adaptor) a of type A is a random number engine that takes values produced by some other random number engine, and applies an algorithm to those values in order to deliver a sequence of values with different randomness properties. An engine b of type B adapted in this way is termed a base engine in this context. The expression a.base() shall be valid and shall return a const reference to a's base engine.

The requirements of a random number engine type shall be interpreted as follows with respect to a random number engine adaptor type.

``` A::A(); ```

Effects: The base engine is initialized as if by its default constructor.

``` bool operator==(const A& a1, const A& a2); ```

Returns: true if a1's base engine is equal to a2's base engine. Otherwise returns false.

``` A::A(result_type s); ```

Effects: The base engine is initialized with s.

``` template<class Sseq> void A::A(Sseq& q); ```

Effects: The base engine is initialized with q.

``` void seed(); ```

Effects: With b as the base engine, invokes b.seed().

``` void seed(result_type s); ```

Effects: With b as the base engine, invokes b.seed(s).

``` template<class Sseq> void seed(Sseq& q); ```

Effects: With b as the base engine, invokes b.seed(q).

A shall also satisfy the following additional requirements:

1. The complexity of each function shall not exceed the complexity of the corresponding function applied to the base engine.

2. The state of A shall include the state of its base engine. The size of A's state shall be no less than the size of the base engine.

3. Copying A's state (e.g., during copy construction or copy assignment) shall include copying the state of the base engine of A.

4. The textual representation of A shall include the textual representation of its base engine.