std::linear_congruential_engine<UIntType,a,c,m>::linear_congruential_engine

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Pseudo-random number generation
 
std::linear_congruential_engine
Member functions
linear_congruential_engine::linear_congruential_engine
Generation
Characteristics
Non-member functions
(C++11)(C++11)(until C++20)
(C++11)(C++11)
 
linear_congruential_engine() : linear_congruential_engine(default_seed) {}
 (1) (since C++11)
explicit linear_congruential_engine( result_type value );
 (2) (since C++11)
template< class SeedSeq >
explicit linear_congruential_engine( SeedSeq& seq );
 (3) (since C++11)
linear_congruential_engine( const linear_congruential_engine& other );
 (4) (since C++11)
(implicitly declared)

Constructs the pseudo-random number engine.

1) The default constructor.
  • If the default-constructed engine is of type std::minstd_rand0, the 10000th consecutive invocation of it produces the value 1043618065.
  • If the default-constructed engine is of type std::minstd_rand, the 10000th consecutive invocation of it produces the value 399268537.
2) Constructs the engine with a seed value value. The engine's initial state is determined as follows:
  • If c % m == 0 and value % m == 0 are both true, the state is 1.
  • Otherwise, the state is value % m.
3) Constructs the engine with a seed sequence seq. Given std::size_t(std::log2(m) / 32) + 1 as k, the engine's initial state is determined as follows:
  1. Creates an invented array object a of length k + 3.
  2. Calls seq.generate(a + 0, a + k + 3).
  3. Let S be (∑k-1
    j=0     a
    j+3    ·232j
    ) mod m    .
  4. If both c % m == 0 and S == 0 are true, sets the engine's state to 1. Otherwise, sets the engine’s state to S.
This overload participates in overload resolution only if SeedSeq meets the requirements of SeedSequence.
4) The copy constructor. Upon construction, *this == other is true.

Parameters

value - seed value to use in the initialization of the internal state
seq - seed sequence to use in the initialization of the internal state

Complexity

1,2) Constant.
3) Same as the complexity of the seq.generate call.
4) Constant.

Exceptions

3) If SeedSeq is not std::seed_seq, throws the exceptions thrown by the seq.generate call.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2181 C++11 overload (3) would not throw even if the seq.generate call throws propagates the exception
P0935R0 C++11 the default constructor was explicit made implicit

See also

 sets the current state of the engine
(public member function)
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