C++ named requirements: RandomNumberEngine

A random number engine is a function object returning unsigned integer values such that each value in the range of possible results has (ideally) equal probability.

Any random number engine is also a UniformRandomBitGenerator, and therefore may be plugged into any random number distribution in order to obtain a random number (formally, a random variate).

Requirements

A type E satisfying UniformRandomBitGenerator will additionally satisfy RandomNumberEngine if, given.

• T, the type named by E::result_type
• s, a value of type T
• e, a non-const value of type E
• v, an lvalue of type E
• x and y, possibly const values of type E
• q, a lvalue of some type satisfying SeedSequence
• z, a value of type unsigned long long
• os, an output stream
• is, an input stream

the following expressions are valid and have their specified effects:

Expression	Return type	Requirements
E()		Creates an engine with the same state as all other default-constructed engines of type E.
E(x)		Creates an engine with the same state as x.
E(s)		Creates an engine whose initial state is determined by the integer s.
E(q)		Creates an engine whose initial state is determined by a single call to q.generate.
e.seed()	void	Sets e == E().
e.seed(s)	void	Sets e == E(s).
e.seed(q)	void	Sets e == E(q).
e()	T	Returns a value in the closed interval [E::min(), E::max()]. Has amortized constant complexity.
e.discard(z)	void	Advances e's state as if by z consecutive calls to e().
x == y	bool	true if x and y are in the same state (such that repeated future calls to x() and y() will produce identical sequences). Otherwise, false.
x != y	bool	!(x == y)
os << x	decltype(os)&	Writes to os the textual representation of x's current state. In the output, adjacent numbers are separated by one or more space characters. If os's fmtflags are not set to ios_base::dec|ios_base::left, the behavior may be undefined.
is >> v	decltype(is)&	Reads from is the textual representation of v's current state, such that if that state was previously written via os << x, then x == v. If is's fmtflags are not set to ios_base::dec, the behavior may be undefined.

Standard library

The following standard library facilities satisfy RandomNumberEngine:

linear_congruential_engine (C++11)	implements linear congruential algorithm (class template)
mersenne_twister_engine (C++11)	implements Mersenne twister algorithm (class template)
subtract_with_carry_engine (C++11)	implements a subtract-with-carry ( lagged Fibonacci) algorithm (class template)
discard_block_engine (C++11)	discards some output of a random number engine (class template)
independent_bits_engine (C++11)	packs the output of a random number engine into blocks of a specified number of bits (class template)
shuffle_order_engine (C++11)	delivers the output of a random number engine in a different order (class template)

The following standard library facilities satisfy UniformRandomBitGenerator but not RandomNumberEngine:

random_device

non-deterministic random number generator using hardware entropy source (class)