duration.h

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// Copyright (c) 2020-2022, The Monero Project
 
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#pragma once
 
#include <chrono>
#include "crypto/crypto.h"
 
namespace crypto
{
  template<typename D>
  struct random_poisson_duration
  {
    using result_type = D;                 
    using rep = typename result_type::rep; 
 
    explicit random_poisson_duration(result_type average)
      : dist(average.count() < 0 ? 0 : average.count())
    {}
 
    result_type operator()()
    {
      crypto::random_device rand{};
      return result_type{dist(rand)};
    }
 
  private:
    std::poisson_distribution<rep> dist;
  };
 
    /* A custom duration is used for subsecond precision because of the
       variance. If 5000 milliseconds is given, 95% of the values fall between
       4859ms-5141ms in 1ms increments (not enough time variance). Providing 1/4
       seconds would yield 95% of the values between 3s-7.25s in 1/4s
       increments. */
 
  using random_poisson_seconds = random_poisson_duration<std::chrono::seconds>;
  using random_poisson_subseconds =
    random_poisson_duration<std::chrono::duration<std::chrono::milliseconds::rep, std::ratio<1, 4>>>;
}