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// Copyright (c) 2020-2023, The Monero Project
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without modification, are
// permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
// conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice, this list
// of conditions and the following disclaimer in the documentation and/or other
// materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its contributors may be
// used to endorse or promote products derived from this software without specific
// prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#pragma once
#include <chrono>
#include "crypto/crypto.h"
namespace crypto
{
//! Generate poisson distributed values in discrete `D` time units.
template<typename D>
struct random_poisson_duration
{
using result_type = D; //!< std::chrono::duration time unit precision
using rep = typename result_type::rep; //!< Type used to represent duration value
//! \param average for generated durations
explicit random_poisson_duration(result_type average)
: dist(average.count() < 0 ? 0 : average.count())
{}
//! Generate a crypto-secure random duration
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. */
//! Generate random durations with 1 second precision
using random_poisson_seconds = random_poisson_duration<std::chrono::seconds>;
//! Generate random duration with 1/4 second precision
using random_poisson_subseconds =
random_poisson_duration<std::chrono::duration<std::chrono::milliseconds::rep, std::ratio<1, 4>>>;
}
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