29 Numerics library [numerics]

29.6 Random number generation [rand]

29.6.7 Utilities [rand.util]

29.6.7.1 Class seed_­seq [rand.util.seedseq]

class seed_seq {
public:
  // types
  using result_type = uint_least32_t;

  // constructors
  seed_seq();
  template<class T>
    seed_seq(initializer_list<T> il);
  template<class InputIterator>
    seed_seq(InputIterator begin, InputIterator end);

  // generating functions
  template<class RandomAccessIterator>
    void generate(RandomAccessIterator begin, RandomAccessIterator end);

  // property functions
  size_t size() const noexcept;
  template<class OutputIterator>
    void param(OutputIterator dest) const;

  // no copy functions
  seed_seq(const seed_seq& ) = delete;
  void operator=(const seed_seq& ) = delete;

private:
  vector<result_type> v;   // exposition only
};
seed_seq();
Effects: Constructs a seed_­seq object as if by default-constructing its member v.
Throws: Nothing.
template<class T> seed_seq(initializer_list<T> il);
Requires: T shall be an integer type.
Effects: Same as seed_­seq(il.begin(), il.end()).
template<class InputIterator> seed_seq(InputIterator begin, InputIterator end);
Requires: InputIterator shall satisfy the requirements of an input iterator type.
Moreover, iterator_­traits<InputIterator>​::​value_­type shall denote an integer type.
Effects: Constructs a seed_­seq object by the following algorithm:
for( InputIterator s = begin; s != end; ++s)
 v.push_back((*s));
template<class RandomAccessIterator> void generate(RandomAccessIterator begin, RandomAccessIterator end);
Requires: RandomAccessIterator shall meet the requirements of a mutable random access iterator.
Moreover, iterator_­traits<RandomAccessIterator>​::​value_­type shall denote an unsigned integer type capable of accommodating 32-bit quantities.
Effects: Does nothing if begin == end.
Otherwise, with and , fills the supplied range according to the following algorithm in which each operation is to be carried out modulo , each indexing operator applied to begin is to be taken modulo n, and T(x) is defined as :
  1. a)
    By way of initialization, set each element of the range to the value 0x8b8b8b8b.
    Additionally, for use in subsequent steps, let and let , where

  2. b)
    With m as the larger of and n, transform the elements of the range: iteratively for , calculate values

    and, in order, increment begin[ by , increment begin[ by , and set begin[k] to .

  3. c)
    Transform the elements of the range again, beginning where the previous step ended: iteratively for , calculate values

    and, in order, update begin[ by xoring it with , update begin[ by xoring it with , and set begin[k] to .

Throws: What and when RandomAccessIterator operations of begin and end throw.
size_t size() const noexcept;
Returns: The number of 32-bit units that would be returned by a call to param().
Complexity: Constant time.
template<class OutputIterator> void param(OutputIterator dest) const;
Requires: OutputIterator shall satisfy the requirements of an output iterator.
Moreover, the expression *dest = rt shall be valid for a value rt of type result_­type.
Effects: Copies the sequence of prepared 32-bit units to the given destination, as if by executing the following statement:
copy(v.begin(), v.end(), dest);
Throws: What and when OutputIterator operations of dest throw.