26 Numerics library [numerics]

26.6 Random number generation [rand]

26.6.3 Requirements [rand.req]

26.6.3.5 Random number engine adaptor requirements [rand.req.adapt]

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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.
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The requirements of a random number engine type shall be interpreted as follows with respect to a random number engine adaptor type.
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A::A();
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Effects: The base engine is initialized as if by its default constructor.
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bool operator==(const A& a1, const A& a2);
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Returns: true if a1's base engine is equal to a2's base engine.
Otherwise returns false.
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A::A(result_type s);
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Effects: The base engine is initialized with s.
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template<class Sseq> A::A(Sseq& q);
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Effects: The base engine is initialized with q.
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void seed();
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Effects: With b as the base engine, invokes b.seed().
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void seed(result_type s);
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Effects: With b as the base engine, invokes b.seed(s).
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template<class Sseq> void seed(Sseq& q);
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Effects: With b as the base engine, invokes b.seed(q).
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A shall also meet the following additional requirements:
  • (10.1)
    The complexity of each function shall not exceed the complexity of the corresponding function applied to the base engine.
  • (10.2)
    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.
  • (10.3)
    Copying A's state (e.g., during copy construction or copy assignment) shall include copying the state of the base engine of A.
  • (10.4)
    The textual representation of A shall include the textual representation of its base engine.