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std::subtract_with_carry_engine

Defined in header <random> 
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.

The state of a subtract_with_carry_engine consists of a sequence \(\small{\{ X_i\}(0 \le i <r)}\){X
i} (0 ≤ i <r), every \(\small{X_i}\)X
i is in interval \(\small{[0, 2^w)}\)[0, 2w
).

Let all subscripts applied to sequence be taken modulo r, c be the carry value which is either 0 or 1. The state transition is performed as follows:

  • let \(\small{Y=X_{i-s}-X_{i-r}-c}\)Y=X
    i-s    -X
    i-r    -c,
  • set \(\small{X_i}\)X
    i     to \(\small{Y \mod 2^w}\)Y mod 2w
    ,
  • set c to 1, if \(\small{Y<0}\)Y<0, to 0 otherwise.

The following typedefs 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>

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, 10 < w <= std::numeric_limits<UIntType>::digits.
s - The short lag.
r - The long lag, where 0 < s < r.

Member types

Member type Definition
result_type (C++11) The integral type generated by the engine. Results are undefined if this is not an unsigned integral type.

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)

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)

Member constants

constexpr size_t word_size
[static] (C++11)
 template parameter w, the word size
(public static member constant)
constexpr size_t short_lag
[static] (C++11)
 template parameter s, the short lag
(public static member constant)
constexpr size_t long_lag
[static] (C++11)
 template parameter r, the long lag
(public static member constant)
constexpr UIntType default_seed
[static] (C++11)
 constant value 19780503u
(public static member constant)

Example

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