std:: subtract_with_carry_engine
|
Defined in header
<random>
|
||
|
template
<
class
UIntType,
|
(since C++11) | |
Is a random number engine that uses subtract with carry algorithm.
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 |
| s | - | the short lag |
| r | - | the long lag |
If
w
is not in
[
1
,
std::
numeric_limits
<
UIntType
>
::
digits
]
, or
s
is not in
[
1
,
r
)
, the program is ill-formed.
Generator properties
The
size
of the states of
subtract_with_carry_engine
is
O(r)
, each of them consists of two parts:
-
A sequence
X
of
r
integer values, where each value is in
[ 0 ,2w). - An integer c (known as the carry ), whose value is either 0 or 1 .
Given that
X
j
stands for the
j mod r
th value (starting from 0) of
X
, the
transition algorithm
of
subtract_with_carry_engine
(
TA(x
i
)
) is defined as follows:
- Let Y be X i-s -X i-r -c .
- Let y be Y mod 2 w , and set X i to y .
- If Y is negative, set c to 1 , otherwise set c to 0 .
The
generation algorithm
of
subtract_with_carry_engine
is
GA(x
i
) = y
, where
y
is the value produced in step 2 of the transition algorithm.
Predefined specializations
The following specializations 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 > |
Nested types
| Type | Definition |
result_type
|
UIntType
|
Data members
|
constexpr
std::size_t
word_size
[static]
|
w
(public static member constant) |
|
constexpr
std::size_t
short_lag
[static]
|
s
(public static member constant) |
|
constexpr
std::size_t
long_lag
[static]
|
r
(public static member constant) |
|
constexpr
std::uint_least32_t
default_seed
[static]
|
19780503u
(public static member constant) |
Member functions
Construction and Seeding |
|
|
constructs the engine
(public member function) |
|
|
sets the current state of the engine
(public member function) |
|
Generation |
|
|
advances the engine's state and returns the generated value
(public member function) |
|
|
advances the engine's state by a specified amount
(public member function) |
|
Characteristics |
|
|
[static]
|
gets the smallest possible value in the output range
(public static member function) |
|
[static]
|
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) |
Example
|
This section is incomplete
Reason: no example |
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3809 | C++11 |
default_seed
might not be
representable with
result_type
|
changed its type to
std::uint_least32_t |