29 Numerics library [numerics]

29.6 Random number generation [rand]

29.6.3 Random number engine class templates [rand.eng]

29.6.3.1 Class template linear_­congruential_­engine [rand.eng.lcong]

A linear_­congruential_­engine random number engine produces unsigned integer random numbers. The state x of a linear_­congruential_­engine object x is of size 1 and consists of a single integer. The transition algorithm is a modular linear function of the form ; the generation algorithm is .

template<class UIntType, UIntType a, UIntType c, UIntType m>
  class linear_congruential_engine {
  public:
    // types
    using result_type = UIntType;

    // engine characteristics
    static constexpr result_type multiplier = a;
    static constexpr result_type increment = c;
    static constexpr result_type modulus = m;
    static constexpr result_type min() { return c == 0u ? 1u: 0u; }
    static constexpr result_type max() { return m - 1u; }
    static constexpr result_type default_seed = 1u;

    // constructors and seeding functions
    explicit linear_congruential_engine(result_type s = default_seed);
    template<class Sseq> explicit linear_congruential_engine(Sseq& q);
    void seed(result_type s = default_seed);
    template<class Sseq> void seed(Sseq& q);

    // generating functions
    result_type operator()();
    void discard(unsigned long long z);
  };

If the template parameter m is 0, the modulus m used throughout this section [rand.eng.lcong] is numeric_­limits<result_­type>​::​max() plus 1. [Note: m need not be representable as a value of type result_­type. end note]

If the template parameter m is not 0, the following relations shall hold: a < m and c < m.

The textual representation consists of the value of x.

explicit linear_congruential_engine(result_type s = default_seed);

Effects: Constructs a linear_­congruential_­engine object. If is 0 and is 0, sets the engine's state to 1, otherwise sets the engine's state to .

template<class Sseq> explicit linear_congruential_engine(Sseq& q);

Effects: Constructs a linear_­congruential_­engine object. With and a an array (or equivalent) of length , invokes q.generate(, ) and then computes . If is 0 and S is 0, sets the engine's state to 1, else sets the engine's state to S.