std::mersenne_twister_engine<UIntType,w,n,m,r,a,u,d,s,b,t,c,l,f>:: mersenne_twister_engine
From cppreference.com
<
cpp
|
numeric
|
random
|
mersenne twister engine
|
mersenne_twister_engine
(
)
:
mersenne_twister_engine
(
default_seed
)
{
}
|
(1) | (since C++11) |
|
explicit
mersenne_twister_engine
(
result_type value
)
;
|
(2) | (since C++11) |
|
template
<
class
SeedSeq
>
explicit mersenne_twister_engine ( SeedSeq & seq ) ; |
(3) | (since C++11) |
|
mersenne_twister_engine
(
const
mersenne_twister_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::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 .
2)
Constructs the engine with a seed value
value
. Given
2
w
as
p
, the engine's initial
state
is determined as follows:
- Sets X -n to value % p .
-
For each integer
i
in
[i - n,- 1], sets X i to [f·(X i-1 xor (X i-1 rshift (w-2)))+i mod n] mod p , where xor and rshift stand for built-in bitwise XOR and bitwise right-shift respectively.
3)
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:
- Creates an invented array object a of length n * k .
- Calls seq. generate ( a + 0 , a + n * k ) .
-
For each integer
i
in
[- n,- 1], sets X i to (∑ k-1j=0 a k(i+n)+j ·2 32j ) mod 2 w . - If the most significant w − r bits of X -n are zero, and if each of the other resulting X i is 0 , changes X -n to 2 w-1 .
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)
O(n)
.
3)
Same as the complexity of the
seq.generate
call.
4)
O(n)
.
Exceptions
Example
|
This section is incomplete
Reason: demos for overloads (2-4) required |
Run this code
#include <cassert> #include <random> 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); }
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) |