29 Numerics library [numerics]

29.6 Random number generation [rand]

29.6.1 Requirements [rand.req]

29.6.1.2 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
:
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 satisfies the requirements of a seed sequence if the expressions shown in Table 94 are valid and have the indicated semantics, and if S also satisfies all other requirements of this subclause [rand.req.seedseq].
In that Table and throughout this subclause:
  1. a)
    T is the type named by S's associated result_­type;
  2. b)
    q is a value of S and r is a possibly const value of S;
  3. c)
    ib and ie are input iterators with an unsigned integer value_­type of at least 32 bits;
  4. d)
    rb and re are mutable random access iterators with an unsigned integer value_­type of at least 32 bits;
  5. e)
    ob is an output iterator; and
  6. f)
    il is a value of initializer_­list<T>.
Table 94 — Seed sequence requirements
Expression
Return type
Pre/post-condition
Complexity
S​::​result_­type
T
T is an unsigned integer type of at least 32 bits.
compile-time
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 .
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 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.
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.