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.
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.
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
[0,2w). - An integer c (known as the carry ), whose value is either 0 or 1.
Given that Xj stands for the j mod rth value (starting from 0) of X, the transition algorithm of subtract_with_carry_engine (TA(xi)) is defined as follows:
- Let Y be Xi-s-Xi-r-c.
- Let y be Y mod 2w
, and set Xi 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(xi) = y, where y is the value produced in step 2 of the transition algorithm.
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> |
Nested types
| Type | Definition |
result_type
|
UIntType
|
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) |
Member functions
Construction and Seeding | |
| constructs the engine (public member function) | |
| sets the current state of the engine (public member function) | |
Generation | |
| advances the engine's state and returns the generated value (public member function) | |
| advances the engine's state by a specified amount (public member function) | |
Characteristics | |
| [static] |
gets the smallest possible value in the output range (public static member function) |
| [static] |
gets the largest possible value in the output range (public static member function) |
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) |
Example
| This section is incomplete Reason: no example |
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 |