std::subtract_with_carry_engine

 

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Uniform random bit generators   uniform_random_bit_generator (C++20) Random number engines linear_congruential_engine (C++11) mersenne_twister_engine (C++11) subtract_with_carry_engine (C++11) philox_engine (C++26) Random number engine adaptors discard_block_engine (C++11) independent_bits_engine (C++11) shuffle_order_engine (C++11) Predefined random number generators Non-deterministic random numbers random_device (C++11) Utilities generate_canonical (C++11) seed_seq (C++11) Random number algorithms ranges::generate_random (C++26) C random library rand    srand    RAND_MAX

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std::subtract_with_carry_engine

Member functions

subtract_with_carry_engine::subtract_with_carry_engine

subtract_with_carry_engine::seed

Generation

subtract_with_carry_engine::operator()

subtract_with_carry_engine::discard

Characteristics

subtract_with_carry_engine::min

subtract_with_carry_engine::max

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 \(\small{\{ X_i\}(0 \le i <r)}\){Xi} (0 ≤ i <r), every \(\small{X_i}\)Xi 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=Xi-s-Xi-r-c,
• set \(\small{X_i}\)Xi 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)	constructs the engine (public member function)
seed	sets the current state of the engine (public member function)
Generation
operator()	advances the engine's state and returns the generated value (public member function)
discard	advances the engine's state by a specified amount (public member function)
Characteristics
min [static]	gets the smallest possible value in the output range (public static member function)
max [static]	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 std::size_t word_size [static] (C++11)	template parameter w, the word size (public static member constant)
constexpr std::size_t short_lag [static] (C++11)	template parameter s, the short lag (public static member constant)
constexpr std::size_t long_lag [static] (C++11)	template parameter r, the long lag (public static member constant)
constexpr std::uint_least32_t default_seed [static] (C++11)	constant value 19780503u (public static member constant)