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std::seed_seq::generate(3) C++ Standard Libary std::seed_seq::generate(3) NAME std::seed_seq::generate - std::seed_seq::generate Synopsis template< class RandomIt > (since C++11) void generate( RandomIt begin, RandomIt end ); 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 se- quence 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 fol- lowing 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 pro- vided by the constructor of this seed_seq object, 1. begin[k+p] += r1 2. begin[k+q] += r2 3. 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[k1]) 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, 1. begin[k+p] ^= r3 2. begin[k+q] ^= r4 3. 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 mod- ulo n. Parameters mutable random-access iterators whose begin, end - std::iterator_traits<>::value_type is an unsigned inte- ger type suitable for storing 32-bit values Type requirements - RandomIt must meet the requirements of LegacyRandomAccessIterator. Return value none, the results are written to the [begin, end) range. Exceptions Only throws if the operations on begin and end throw. Example // Run this code #include <algorithm> #include <cassert> #include <cstdint> #include <iostream> #include <random> // Prototyping the main part of std::seed_seq... struct seed_seq { std::vector<std::uint32_t> v; seed_seq(std::initializer_list<std::uint32_t> const il) : v{il} {} template <typename RandomIt> void generate(RandomIt first, RandomIt last) { if (first == last) return; // // Assuming v = {1,2,3,4,5} and distance(first, last) == 10. // // Step 1: fill with 0x8b8b8b8b // seeds = {2341178251, 2341178251, 2341178251, 2341178251, 2341178251, // 2341178251, 2341178251, 2341178251, 2341178251, 2341178251 } // std::fill(first, last, 0x8b8b8b8b); // // Step 2: // n = 10, s = 5, t = 3, p = 3, q = 6, m = 10 // const std::uint32_t n = last - first; const std::uint32_t s = v.size(); const std::uint32_t t = (n < 7) ? (n - 1) / 2 : (n < 39) ? 3 : (n < 68) ? 5 : (n < 623) ? 7 : 11; const std::uint32_t p = (n - t) / 2; const std::uint32_t q = p + t; const std::uint32_t m = std::max(s + 1, n); // // 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 } // auto begin_mod = [first, n](std::uint32_t u) -> de- cltype(*first)& { return first[u % n]; // i.e. begin[x] is taken modulo n }; auto T = [](std::uint32_t x) { return x ^ (x >> 27); }; for (std::uint32_t k = 0, r1, r2; k < m; ++k) { r1 = 1664525 * T(begin_mod(k) ^ begin_mod(k + p) ^ be- gin_mod(k - 1)); r2 = (k == 0) ? r1 + s : (k <= s) ? r1 + k % n + v[k - 1] : r1 + k % n; begin_mod(k + p) += r1; begin_mod(k + q) += r2; begin_mod(k) = r2; } // // 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 k = m, r3, r4; k < m + n; ++k) { r3 = 1566083941 * T(begin_mod(k) + begin_mod(k+p) + be- gin_mod(k-1)); r4 = r3 - k%n; begin_mod(k+p) ^= r3; begin_mod(k+q) ^= r4; begin_mod(k) = r4; } } }; int main() { const auto input = std::initial- izer_list<std::uint32_t>{1,2,3,4,5}; const auto output_size = 10; // using std version of seed_seq std::seed_seq seq(input); std::vector<std::uint32_t> seeds(output_size); seq.generate(seeds.begin(), seeds.end()); for(const std::uint32_t n : seeds) { std::cout << n << '\n'; } // using custom version of seed_seq seed_seq seq2(input); std::vector<std::uint32_t> seeds2(output_size); seq2.generate(seeds2.begin(), seeds2.end()); assert(seeds == seeds2); } Output: 4204997637 4246533866 1856049002 1129615051 690460811 1075771511 46783058 3904109078 1534123438 1495905678 http://cppreference.com 2022.07.31 std::seed_seq::generate(3)
NAME | Synopsis | Parameters | Type requirements | Return value | Exceptions | Example | Output:
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