std::mersenne_twister_engine<UIntType,w,n,m,r,a,u,d,s,b,t,c,l,f>::mersenne_twister_engine - cppreference.com (original) (raw)

Constructs the pseudo-random number engine.

1. The default constructor.

• If the default-constructed engine is of type std::mt19937, the 10000th consecutive invocation of it produces the value 4123659995.
• If the default-constructed engine is of type std::mt19937_64, the 10000th consecutive invocation of it produces the value 9981545732273789042.

1. Constructs the engine with a seed value value. Given \(\scriptsize 2^w \)2w
   as p, the engine's initial state is determined as follows:

1. Sets \(\scriptsize X_{-n} \)X-n to value % p.
2. For each integer i in [i - n, -1], sets \(\scriptsize X_i \)Xi to \(\scriptsize [f \cdot (X_{i-1}\ \mathsf{xor}\ (X_{i-1}\ \mathsf{rshift}\ (w-2)))+i \mod n] \mod p \)[f·(Xi-1 xor (Xi-1 rshift (w-2)))+i mod n] mod p, where \(\scriptsize \mathsf{xor} \)xor and \(\scriptsize \mathsf{rshift} \)rshift stand for built-in bitwise XOR and bitwise right-shift respectively.

1. Constructs the engine with a seed sequence seq. Given std::size_t(w / 32) + 1 as k, the engine's initial state is determined as follows:

1. Creates an invented array object a of length n * k.
2. Calls seq.generate(a + 0, a + n * k).
3. For each integer i in [-n, -1], sets \(\scriptsize X_{i} \)Xi to \(\scriptsize (\sum^{k-1}_{j=0} a_{k(i+n)+j} \cdot 2^{32j}) \mod 2^w \)(∑k-1
   j=0 ak(i+n)+j·232j
   ) mod 2w
   .
4. If the most significant w − r bits of \(\scriptsize X_{-n} \)X-n are zero, and if each of the other resulting \(\scriptsize X_{i} \)Xi is ​0​, changes \(\scriptsize X_{-n} \)X-n to \(\scriptsize 2^{w-1} \)2w-1
   .

This overload participates in overload resolution only if SeedSeq meets the requirements of SeedSequence.

1. The copy constructor. Upon construction, *this == other is true.

[edit] Parameters

[edit] Complexity

1,2) \(\scriptsize O(n) \)O(n).

1. Same as the complexity of the seq.generate call.

2. \(\scriptsize O(n) \)O(n).

[edit] Exceptions

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

[edit] Example

#include #include   int main() { std::mt19937 gen32; // overload (1) std::mt19937_64 gen64; // overload (1) gen32.discard(10000 - 1); gen64.discard(10000 - 1); assert(gen32() == 4123659995); assert(gen64() == 9981545732273789042ull); }

[edit] Defect reports

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

[edit] See also

| | sets the current state of the engine (public member function) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |