template< class RandomIt > void generate( RandomIt begin, RandomIt end ); | (since C++11) |
Fills the range [begin, end) with unsigned integer values i, 0 ≤ i < 232
, based on the data originally provided in the constructor of this seed_seq. The produced values are distributed over the entire 32-bit range even if the initial values were strongly biased.
The following algorithm is used (adapted from the initialization sequence of the Mersenne Twister generator by Makoto Matsumoto and Takuji Nishimura, incorporating the improvements made by Mutsuo Saito in 2007).
- If
begin == end, do nothing. Otherwise, - First, set each element of the output range to the value
0x8b8b8b8b - Transform the elements of the output range according to the following algorithm:
For k = 0,..., m-1
.
where m=max(s+1, n)
and n=end-begin
and s=v.size()
and v is the private container holding the values originally provided by the constructor of this seed_seq object,
-
begin[k+p] += r1 -
begin[k+q] += r2 -
begin[k] = r2,
where p=(n-t)/2
and q=p+t
and t=(n >= 623) ? 11 : (n >= 68) ? 7 : (n >= 39) ? 5 : (n >= 7) ? 3 : (n - 1) / 2
and r1=1664525 * T(begin[k]^begin[k+p]^begin[k−1])
and T(x) = x ^ (x >> 27)
and r2=r1+s if k==0, r2=r1 + k%n + v[k-1] if 0<k<=s, r2=r1 + k%n if k>s.
For k = m,..., m+n-1,
-
begin[k+p] ^= r3 -
begin[k+q] ^= r4 -
begin[k]=r4
where r3 = 1566083941 * T(begin[k]+begin[k+p]+begin[k-1])
and r4=r3 - k%n.
where all calculations are performed modulo 232
and where the indexing of the output range (begin[x]) is taken modulo n.
Parameters
| begin, end | - | mutable random-access iterators whose std::iterator_traits<>::value_type is an unsigned integer type suitable for storing 32-bit values |
| Type requirements | ||
- RandomIt must meet the requirements of RandomAccessIterator. | ||
Return value
none, the results are written to the [begin, end) range.
Exceptions
Only throws if the operations on begin and end throw.
Example
#include <random>
#include <iostream>
int main()
{
std::seed_seq seq({1,2,3,4,5});
std::vector<std::uint32_t> seeds(10);
seq.generate(seeds.begin(), seeds.end());
// Step 1: fill with 0x8b8b8b8b
// seeds = {2341178251, 2341178251, 2341178251, 2341178251, 2341178251,
// 2341178251, 2341178251, 2341178251, 2341178251, 2341178251 }
//
// Step 2:
// n = 10, s = 5, t = 3, p = 3, q = 6, m = 10
//
// First iteration, k = 0; r1 = 1371501266, r2 = 1371501271
//
// seeds = {1371501271, 2341178251, 2341178251, 3712679517, 2341178251,
// 2341178251, 3712679522, 2341178251, 2341178251, 2341178251 }
//
// Iterations from k = 1 to k = 5 (r2 = r1 + k%n + v[k-1])
//
// r1 = 2786190137, 3204727651, 4173325571, 1979226628, 401983366
// r2 = 2786190139, 3204727655, 4173325577, 1979226636, 401983376
//
// seeds = {3350727907, 3188173515, 3204727655, 4173325577, 1979226636,
// 401983376, 3591037797, 2811627722, 1652921976, 2219536532 }
//
// Iterations from k = 6 to k = 9 (r2 = r1 + k%n)
//
// r1 = 2718637909, 1378394210, 2297813071, 1608643617
// r2 = 2718637915, 1378394217, 2297813079, 1608643626
//
// seeds = { 434154821, 1191019290, 3237041891, 1256752498, 4277039715,
// 2010627002, 2718637915, 1378394217, 2297813079, 1608643626 }
//
// Step 3
// iterations from k = 10 to k = 19, using ^= to modify the output
//
// r1 = 1615303485, 3210438310, 893477041, 2884072672, 1918321961,
// r2 = 1615303485, 3210438309, 893477039, 2884072669, 1918321957
//
// seeds = { 303093272, 3210438309, 893477039, 2884072669, 1918321957,
// 1117182731, 1772877958, 2669970405, 3182737656, 4094066935 }
//
// r1 = 423054846, 46783064, 3904109085, 1534123446, 1495905687
// r2 = 423054841, 46783058, 3904109078, 1534123438, 1495905678
//
// seeds = { 4204997637, 4246533866, 1856049002, 1129615051, 690460811,
// 1075771511, 46783058, 3904109078, 1534123438, 1495905678 }
for(std::uint32_t n : seeds)
std::cout << n << '\n';
}Output:
4204997637 4246533866 1856049002 1129615051 690460811 1075771511 46783058 3904109078 1534123438 1495905678
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