std::subtract_with_carry_engine - cppreference.com (original) (raw)

std::subtract_with_carry_engine

Is a random number engine that uses subtract with carry algorithm.

Contents

• 1 Template parameters
• 2 Generator properties
• 3 Predefined specializations
• 4 Nested types
• 5 Data members
• 6 Member functions
  • 6.1 Construction and Seeding
  • 6.2 Generation
  • 6.3 Characteristics
• 7 Non-member functions
• 8 Example
• 9 Defect reports

[edit] Template parameters

If w is not in [1, std::numeric_limits<UIntType>::digits], or s is not in [1, r), the program is ill-formed.

[edit] Generator properties

The size of the states of subtract_with_carry_engine is \(\scriptsize O(r)\)O(r), each of them consists of two parts:

• A sequence X of r integer values, where each value is in [​0​, 2 w
).
• An integer c (known as the carry ), whose value is either ​0​ or 1.

Given that \(\scriptsize X_j\)Xj stands for the \(\scriptsize j\mod r\)j mod rth value (starting from 0) of X, the transition algorithm of subtract_with_carry_engine (\(\scriptsize TA(x_i)\)TA(xi)) is defined as follows:

1. Let Y be \(\scriptsize X_{i-s}-X_{i-r}-c\)Xi-s-Xi-r-c.
2. Let y be \(\scriptsize Y\mod 2^w\)Y mod 2w
   , and set \(\scriptsize X_i\)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 \(\scriptsize GA(x_i) = y\)GA(xi) = y, where y is the value produced in step 2 of the transition algorithm.

[edit] Predefined specializations

The following specializations define the random number engine with two commonly used parameter sets:

[edit] Nested types

[edit] Data members

| | w (public static member constant) | | -------------------------------------------- | | | s (public static member constant) | | | r (public static member constant) | | | 19780503u (public static member constant) |

[edit] Member functions

[edit] Non-member functions

[edit] Example

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.