FastIntDistribution.hpp

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#ifndef SOLIDUTILS_INCLUDE_FASTINTDISTRIBUTION_HPP
#define SOLIDUTILS_INCLUDE_FASTINTDISTRIBUTION_HPP


#include <cstdint>
#include <limits>


namespace sl
{

template<typename T>
class FastIntDistribution
{
  public:
  FastIntDistribution(
      T const min,
      T const max) :
    m_min(min),
    m_range(static_cast<uint64_t>(max-min)+1)
  {
    // do nothing
  }

  template<class RNG>
  T operator()(RNG& rng)
  {
    static_assert(std::numeric_limits<uint64_t>::max() > \
        static_cast<uint64_t>(RNG::max() - RNG::min()), \
        "Unhandled full 64 bit range.");

    constexpr uint64_t RNG_RANGE = static_cast<uint64_t>(RNG::max() - RNG::min()) + 1;

    uint64_t const width = m_range / RNG_RANGE;

    uint64_t num = 0;
    for (uint64_t i = 0; i <= width; ++i) {
      num *= static_cast<uint64_t>(RNG_RANGE);
      num += static_cast<uint64_t>(rng() - RNG::min());
    }
    num = num % m_range;
    
    return static_cast<T>(num) + m_min;
  }

  private:
  T m_min;
  uint64_t m_range;

};


}

#endif