26 Numerics library [numerics]

26.6 Random number generation [rand]

26.6.5 Random number engine adaptor class templates [rand.adapt]

26.6.5.4 Class template shuffle_­order_­engine [rand.adapt.shuf]

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A shuffle_­order_­engine random number engine adaptor produces the same random numbers that are produced by some base engine e, but delivers them in a different sequence.
The state x of a shuffle_­order_­engine engine adaptor object x consists of the state e of its base engine e, an additional value Y of the type delivered by e, and an additional sequence V of k values also of the type delivered by e.
The size of the state is the size of e's state plus .
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The transition algorithm permutes the values produced by e.
The state transition is performed as follows:
  • (2.1)
    Calculate an integer .
  • (2.2)
    Set Y to and then set to e().
3
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The generation algorithm yields the last value of Y produced while advancing e's state as described above.
template<class Engine, size_t k> class shuffle_order_engine { public: // types using result_type = typename Engine::result_type; // engine characteristics static constexpr size_t table_size = k; static constexpr result_type min() { return Engine::min(); } static constexpr result_type max() { return Engine::max(); } // constructors and seeding functions shuffle_order_engine(); explicit shuffle_order_engine(const Engine& e); explicit shuffle_order_engine(Engine&& e); explicit shuffle_order_engine(result_type s); template<class Sseq> explicit shuffle_order_engine(Sseq& q); void seed(); void seed(result_type s); template<class Sseq> void seed(Sseq& q); // generating functions result_type operator()(); void discard(unsigned long long z); // property functions const Engine& base() const noexcept { return e; }; private: Engine e; // exposition only result_type V[k]; // exposition only result_type Y; // exposition only };
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The following relation shall hold: 0 < k.
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The textual representation consists of the textual representation of e, followed by the k values of V, followed by the value of Y.
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In addition to its behavior pursuant to subclause [rand.req.adapt], each constructor that is not a copy constructor initializes and Y, in that order, with values returned by successive invocations of e().