std::generate_canonical (3) - Linux Manuals

std::generate_canonical: std::generate_canonical

NAME

std::generate_canonical - std::generate_canonical

Synopsis

Defined in header <random>
template< class RealType, size_t bits, class Generator > (since C++11)
RealType generate_canonical( Generator& g );

Generates a random floating point number in range [0, 1).
To generate enough entropy, generate_canonical() will call g() exactly k times, where \(k = max(1, \lceil \frac{b}{log_2 R} \rceil)\)k = max(1, ⌈ b / log
2 R ⌉) and

* b = std::min<std::size_t>(bits, std::numeric_limits<RealType>::digits)
* R = g.max() - g.min() + 1.

Parameters

g - generator to use to acquire entropy

Return value

Floating point value in range [0, 1).

Exceptions

None except from those thrown by g

Notes

Some existing implementations have a bug where they may occasionally return 1.0 if RealType is float GCC_#63176 LLVM_#18767. This is LWG_issue_2524

Example

produce random numbers with 10 bits of randomness: this may produce only k*R distinct values
// Run this code

  #include <random>
  #include <iostream>

  int main()
  {
      std::random_device rd;
      std::mt19937 gen(rd());
      for(int n=0; n<10; ++n) {
          std::cout << std::generate_canonical<double, 10>(gen) << ' ';
      }
  }

Possible output:

  0.208143 0.824147 0.0278604 0.343183 0.0173263 0.864057 0.647037 0.539467 0.0583497 0.609219