< cpp‎ | numeric‎ | random
Pseudo-random number generation
Uniform random bit generators
Engines and engine adaptors
Non-deterministic generator
Uniform distributions
Bernoulli distributions
Poisson distributions
Normal distributions
Sampling distributions
Seed Sequences
C library
Defined in header <random>

    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 {X
} (0 ≤ i <r)
, every X
is in interval [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 Y=X
  • set X
    to Y mod 2w
  • set c to 1, if 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>[edit]
ranlux48_base (C++11) std::subtract_with_carry_engine<std::uint_fast64_t, 48, 5, 12>[edit]


[edit] 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.

[edit] 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.

[edit] Member functions

Construction and Seeding
constructs the engine
(public member function) [edit]
sets the current state of the engine
(public member function) [edit]
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]
[static] (C++11)
gets the smallest possible value in the output range
(public static member function) [edit]
[static] (C++11)
gets the largest possible value in the output range
(public static member function) [edit]

[edit] Non-member functions

(C++11)(C++11)(removed in C++20)
compares the internal states of two pseudo-random number engines
(function) [edit]
performs stream input and output on pseudo-random number engine
(function template) [edit]

[edit] 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)

[edit] Example