97 lines
3.3 KiB
Markdown
97 lines
3.3 KiB
Markdown
[rand.general]
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# 29 Numerics library [[numerics]](./#numerics)
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## 29.5 Random number generation [[rand]](rand#general)
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### 29.5.1 General [rand.general]
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L1279)
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Subclause [[rand]](rand "29.5 Random number generation") defines a facility
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for generating (pseudo-)random numbers[.](#1.sentence-1)
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L1283)
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In addition to a few utilities,
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four categories of entities are described:[*uniform random bit generators*](#def:uniform_random_bit_generators),[*random number engines*](#def:random_number_engines),[*random number engine adaptors*](#def:random_number_engine_adaptors),
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and[*random number distributions*](#def:random_number_distributions)[.](#2.sentence-1)
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These categorizations are applicable
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to types that meet the corresponding requirements,
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to objects instantiated from such types,
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and to templates producing such types when instantiated[.](#2.sentence-2)
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[*Note [1](#note-1)*:
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These entities are specified in such a way
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as to permit the binding
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of any uniform random bit generator object e as the argument
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to any random number distribution object d,
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thus producing a zero-argument function object
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such as given by bind(d,e)[.](#2.sentence-3)
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â *end note*]
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L1306)
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Each of the entities specified in [[rand]](rand "29.5 Random number generation") has an associated arithmetic type ([[basic.fundamental]](basic.fundamental "6.9.2 Fundamental types"))
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identified as result_type[.](#3.sentence-1)
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With T as the result_type thus associated with such an entity,
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that entity is characterized:
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- [(3.1)](#3.1)
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as [*boolean*](#def:boolean) or equivalently as [*boolean-valued*](#def:boolean-valued),
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if T is bool;
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- [(3.2)](#3.2)
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otherwise
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as [*integral*](#def:integral) or equivalently as [*integer-valued*](#def:integer-valued),
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if numeric_limits<T>::is_integer is true;
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- [(3.3)](#3.3)
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otherwise
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as [*floating-point*](#def:floating-point) or equivalently as [*real-valued*](#def:real-valued)[.](#3.sentence-2)
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If integer-valued,
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an entity may optionally be further characterized as[*signed*](#def:signed) or [*unsigned*](#def:unsigned),
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according to numeric_limits<T>::is_signed[.](#3.sentence-3)
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L1331)
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Unless otherwise specified,
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all descriptions of calculations
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in [[rand]](rand "29.5 Random number generation") use mathematical real numbers[.](#4.sentence-1)
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/numerics.tex#L1337)
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Throughout [[rand]](rand "29.5 Random number generation"),
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the operatorsbitand, bitor, and xor denote the respective conventional bitwise operations[.](#5.sentence-1)
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Further:
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- [(5.1)](#5.1)
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the operator rshift denotes a bitwise right shift
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with zero-valued bits appearing in the high bits of the result, and
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- [(5.2)](#5.2)
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the operator lshiftw denotes a bitwise left shift
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with zero-valued bits appearing in the low bits of the result,
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and whose result is always taken modulo 2w[.](#5.sentence-2)
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