std::subtract_with_carry_engine

 

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std::subtract_with_carry_engine

Member functions

subtract_with_carry_engine::subtract_with_carry_engine (C++11)

subtract_with_carry_engine::seed (C++11)

Generation

subtract_with_carry_engine::operator() (C++11)

subtract_with_carry_engine::discard (C++11)

Characteristics

subtract_with_carry_engine::min (C++11)

subtract_with_carry_engine::max (C++11)

Non-member functions

operator==operator!= (C++11)(C++11)(until C++20)

operator<<operator>> (C++11)(C++11)

 

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
(constructor) (C++11)	constructs the engine (public member function)
seed (C++11)	sets the current state of the engine (public member function)
Generation
operator() (C++11)	advances the engine's state and returns the generated value (public member function)
discard (C++11)	advances the engine's state by a specified amount (public member function)
Characteristics
min [static] (C++11)	gets the smallest possible value in the output range (public static member function)
max [static] (C++11)	gets the largest possible value in the output range (public static member function)

Non-member functions

operator==operator!= (C++11)(C++11)(removed in C++20)	compares the internal states of two pseudo-random number engines (function)
operator<<operator>> (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)