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cppdraft/rand/general.md

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