std::subtract_with_carry_engine
Defined in header <random>
|
||
template< class UIntType, |
(since C++11) | |
Is a random number engine that uses subtract with carry algorithm.
Contents |
[edit] Template parameters
UIntType | - | The result type generated by the generator. The effect is undefined if this is not one of unsigned short, unsigned int, unsigned long, or unsigned long long. |
w | - | the word size, in bits, of the state sequence |
s | - | the short lag |
r | - | the long lag |
If w is not in [
1,
std::numeric_limits<UIntType>::digits]
, or s is not in [
1,
r)
, the program is ill-formed.
[edit] Generator properties
The size of the states of subtract_with_carry_engine
is O(r), each of them consists of two parts:
- A sequence X of r integer values, where each value is in
[
0,
2
w
)
. - An integer c (known as the carry ), whose value is either 0 or 1.
Given that X
j stands for the j mod rth value (starting from 0) of X, the transition algorithm of subtract_with_carry_engine
(TA(x
i)) is defined as follows:
- Let Y be X
i-s-X
i-r-c. - Let y be Y mod 2w
, and set X
i to y. - If Y is negative, set c to 1, otherwise set c to 0.
The generation algorithm of subtract_with_carry_engine
is GA(x
i) = y, where y is the value produced in step 2 of the transition algorithm.
[edit] Predefined specializations
The following specializations define the random number engine with two commonly used parameter sets:
Defined in header
<random> | |
Type | Definition |
ranlux24_base (C++11)
|
std::subtract_with_carry_engine<std::uint_fast32_t, 24, 10, 24> |
ranlux48_base (C++11)
|
std::subtract_with_carry_engine<std::uint_fast64_t, 48, 5, 12> |
[edit] Nested types
Type | Definition |
result_type
|
UIntType
|
[edit] Data members
constexpr std::size_t word_size [static] |
w (public static member constant) |
constexpr std::size_t short_lag [static] |
s (public static member constant) |
constexpr std::size_t long_lag [static] |
r (public static member constant) |
constexpr std::uint_least32_t default_seed [static] |
19780503u (public static member constant) |
[edit] Member functions
Construction and Seeding | |
(C++11) |
constructs the engine (public member function) |
(C++11) |
sets the current state of the engine (public member function) |
Generation | |
(C++11) |
advances the engine's state and returns the generated value (public member function) |
(C++11) |
advances the engine's state by a specified amount (public member function) |
Characteristics | |
[static] (C++11) |
gets the smallest possible value in the output range (public static member function) |
[static] (C++11) |
gets the largest possible value in the output range (public static member function) |
[edit] Non-member functions
(C++11)(C++11)(removed in C++20) |
compares the internal states of two pseudo-random number engines (function) |
(C++11) |
performs stream input and output on pseudo-random number engine (function template) |
[edit] Example
This section is incomplete Reason: no example |
[edit] 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 3809 | C++11 | default_seed might not berepresentable with result_type
|
changed its type to std::uint_least32_t |