First, the function advances the internal state by one using a transition algorithm that produces a twist on the selected element in the state as if this was x[i] in the following piece of code:
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UIntType Mask = (1u<<w)-1, UMask= (Mask << r) & Mask, LMask = (~UMask) & Mask, Y = (x[i]&UMask)|(x[(i+1)%n]&LMask); // upper bits of x[i] and lower of x[i+1] x[i]=x[(i+m)%n]^(Y>>1)^((Y&1)*a); // mersenne twister linear transformation
With each of the values being their corresponding class template parameters.
To improve the uniformity of the random value produced, the function uses a generation algorithm to return a tempered version of the selected element in the state sequence: it applies the same transformation applied on y in the following piece of code:
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y^=(y>>u)&d; y^=(y<<s)&b; y^=(y<<t)&c; y^=y>>l;
With each of the values being again their corresponding class template parameters.
Note: not fully tested, plese report any inaccuracies.
Parameters
None
Return value
A new random number. result_type is a member type, defined as an alias of the first class template parameter (UIntType).
Example
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// mersenne_twister_engine::operator() #include <iostream> #include <chrono> #include <random> int main () { // obtain a seed from the system clock: unsigned seed = std::chrono::system_clock::now().time_since_epoch().count(); std::mt19937 generator (seed); // mt19937 is a standard mersenne_twister_engine std::cout << "Random value: " << generator() << std::endl; return 0; }