std::subtract_with_carry_engine<UIntType,w,s,r>:: subtract_with_carry_engine
From cppreference.com
<
cpp
|
numeric
|
random
|
subtract with carry engine
|
subtract_with_carry_engine
(
)
:
subtract_with_carry_engine
(
0u
)
{
}
|
(1) | (since C++11) |
|
explicit
subtract_with_carry_engine
(
result_type value
)
;
|
(2) | (since C++11) |
|
template
<
class
SeedSeq
>
explicit subtract_with_carry_engine ( SeedSeq & seq ) ; |
(3) | (since C++11) |
|
subtract_with_carry_engine
(
const
subtract_with_carry_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::ranlux24_base, the 10000th consecutive invocation of it produces the value 7937952 . -
If the default-constructed engine is of type
std::ranlux48_base, the 10000th consecutive invocation of it produces the value 61839128582725 .
2)
Constructs the engine with a seed value
value
. The sequence
X
of the engine's initial
state
is determined as follows:
- Constructs a std:: linear_congruential_engine < std:: uint_least32_t , 40014u, 0u, 2147483563u > object e with argument value == 0u ? default_seed : value .
- Let n be std:: size_t ( w / 32 ) + 1 .
- Sets the values of X -r , ..., X -1 , in that order. Each value X i is set as specified below:
-
- Successively calls e for n times, the return values are denoted as z 0 ... z n-1 .
- Sets X i to (∑ n-1j=0 z j ·2 32j ) mod m .
If
X
-1
is
0
, sets the carry value
c
of the engine's initial state to
1
. Otherwise, sets
c
to
0
.
3)
Constructs the engine with a seed sequence
seq
. Given
std::
size_t
(
w
/
32
)
+
1
as
k
, the sequence
X
of the engine's initial
state
is determined as follows:
- Creates an invented array object a of length r * k .
- Calls seq. generate ( a + 0 , a + r * k ) .
-
For each integer
i
in
[- r,- 1], sets X i to (∑ k-1j=0 a k(i+r)+j ·2 32j ) mod m .
If
X
-1
is
0
, sets the carry value
c
of the engine's initial state to
1
. Otherwise, sets
c
to
0
.
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
3)
Same as the complexity of the
seq.generate
call.
4)
O(r)
.
Exceptions
Example
|
This section is incomplete
Reason: demos for overloads (2-4) required |
Run this code
#include <cassert> #include <random> int main() { std::ranlux24_base gen24; // overload (1) std::ranlux48_base gen48; // overload (1) gen24.discard(10000 - 1); gen48.discard(10000 - 1); assert(gen24() == 7'937'952); assert(gen48() == 61'839'128'582'725); }
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 |
| LWG 3809 | C++11 |
e
could not be constructed if
result_type
is
std::uint16_t
|
e can be constructed in this case |
| P0935R0 | C++11 | the default constructor was explicit | made implicit |
See also
|
sets the current state of the engine
(public member function) |