28 Numerics library [numerics]

28.5 Random number generation [rand]

28.5.3 Requirements [rand.req] Seed sequence requirements [rand.req.seedseq]

A seed sequence is an object that consumes a sequence of integer-valued data and produces a requested number of unsigned integer values i, , 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]
A class S meets the requirements of a seed sequence if the expressions shown in Table 98 are valid and have the indicated semantics, and if S also meets all other requirements of this subclause [rand.req.seedseq].
In that Table and throughout this subclause:
  • T is the type named by S's associated result_type;
  • q is a value of type S and r is a value of type S or const S;
  • ib and ie are input iterators with an unsigned integer value_type of at least 32 bits;
  • rb and re are mutable random access iterators with an unsigned integer value_type of at least 32 bits;
  • ob is an output iterator; and
  • il is a value of type initializer_list<T>.
Table 98: Seed sequence requirements [tab:rand.req.seedseq]
Return type
T is an unsigned integer type of at least 32 bits.
Creates a seed sequence with the same initial state as all other default-constructed seed sequences of type S.
Creates a seed sequence having internal state that depends on some or all of the bits of the supplied sequence [ib,ie).
Same as S(il.begin(), il.end()).
same as S(il.begin(), il.end())
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.
The number of 32-bit units that would be copied by a call to r.param.
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.