cppdraft_translate/cppdraft/rand/req/seedseq.md

[rand.req.seedseq]

29 Numerics library [numerics]

29.5 Random number generation [rand]

29.5.3 Requirements [rand.req]

29.5.3.2 Seed sequence requirements [rand.req.seedseq]

1

#

A seed sequence is an object that consumes a sequence of integer-valued data and produces a requested number of unsigned integer values i, 0≤i<232, based on the consumed data.

[Note 1:

Such an object provides a mechanism to avoid replication of streams of random variates.

This can be useful, for example, in applications requiring large numbers of random number engines.

— end note]

2

#

A class S meets the requirements of a seed sequence if the expressions shown in Table 126 are valid and have the indicated semantics, and if S also meets all other requirements of [rand.req.seedseq].

In Table 126 and throughout this subclause:

• (2.1)

T is the type named by S's associated result_type;

• (2.2)

q is a value of type S and r is a value of type S or const S;

• (2.3)

ib and ie are input iterators with an unsigned integer value_type of at least 32 bits;

• (2.4)

rb and re are mutable random access iterators with an unsigned integer value_type of at least 32 bits;

• (2.5)

ob is an output iterator; and

• (2.6)

il is a value of type initializer_list.

Table 126 — Seed sequence requirements [tab:rand.req.seedseq]

🔗 Expression	Return type	Pre/post-condition	Complexity
🔗 S​::​result_type	T	T is an unsigned integer type of at least 32 bits.
🔗 S()		Creates a seed sequence with the same initial state as all other default-constructed seed sequences of type S.	constant
🔗 S(ib,ie)		Creates a seed sequence having internal state that depends on some or all of the bits of the supplied sequence [ib,ie).	O(ie−ib)
🔗 S(il)		Same as S(il.begin(), il.end()).	same as S(il.begin(), il.end())
🔗 q.generate(rb,re)	void	Does nothing if rb == re. Otherwise, fills the supplied sequence [rb,re) with 32-bit quantities that depend on the sequence supplied to the constructor and possibly also depend on the history of generate's previous invocations.	O(re−rb)
🔗 r.size()	size_t	The number of 32-bit units that would be copied by a call to r.param.	constant
🔗 r.param(ob)	void	Copies to the given destination a sequence of 32-bit units that can be provided to the constructor of a second object of type S, and that would reproduce in that second object a state indistinguishable from the state of the first object.	O(r.size())