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std::subtract_with_carry_engine - cppreference.com

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template< class UIntType, std::size_t w, std::size_t s, std::size_t r > class subtract_with_carry_engine;

 (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:

  1. Let Y be Xi-s-Xi-r-c.
  2. Let y be Y mod 2w
    , and set Xi to y.
  3. 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:

Type Definition
ranlux24_base (C++11) std::subtract_with_carry_engine<std::uint_fast32_t, 24, 10, 24>[edit]
ranlux48_base (C++11) std::subtract_with_carry_engine<std::uint_fast64_t, 48, 5, 12>[edit]

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) [edit]
sets the current state of the engine
(public member function) [edit]
Generation
advances the engine's state and returns the generated value
(public member function) [edit]
advances the engine's state by a specified amount
(public member function) [edit]
Characteristics

[static]

 gets the smallest possible value in the output range
(public static member function) [edit]

[static]

 gets the largest possible value in the output range
(public static member function) [edit]

Non-member functions

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 be
representable with result_type 		changed its type to
std::uint_least32_t