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/* Copyright (c) 2019-2025. The SimGrid Team. All rights reserved. */
/* This program is free software; you can redistribute it and/or modify it
* under the terms of the license (GNU LGPL) which comes with this package. */
#ifndef SIMGRID_XBT_RANDOM_HPP
#define SIMGRID_XBT_RANDOM_HPP
#include "xbt/base.h"
#include <fstream>
#include <iostream>
#include <random>
#include <string>
namespace simgrid::xbt::random {
/** A random number generator.
*
* It uses a std::mersenne_twister_engine (std::mt19937) and provides several distributions.
* This interface is implemented by StdRandom and XbtRandom.
*/
class XBT_PUBLIC Random {
public:
std::mt19937 mt19937_gen; // the random number engine
/** @brief Build a new random number generator with default seed */
Random() = default;
/** @brief Build a new random number generator with given seed */
explicit Random(int seed) : mt19937_gen(seed) {}
virtual ~Random() = default;
/**
* @brief Sets the seed of the Mersenne-Twister RNG
*/
void set_seed(int seed) { mt19937_gen.seed(seed); }
/**
* @brief Read the state of the Mersenne-Twister RNG from a file
*/
bool read_state(const std::string& filename);
/**
* @brief Write the state of the Mersenne-Twister RNG to a file
*/
bool write_state(const std::string& filename) const;
/**
* @brief Draws an integer number uniformly in range [min, max] (min and max included)
*
* @param min Minimum value
* @param max Maximum value
*/
virtual int uniform_int(int min, int max) = 0;
/**
* @brief Draws a real number uniformly in range [min, max) (min included, and max excluded)
*
* @param min Minimum value
* @param max Maximum value
*/
virtual double uniform_real(double min, double max) = 0;
/**
* @brief Draws a real number according to the given exponential distribution
*
* @param lambda Parameter of the exponential law
*/
virtual double exponential(double lambda) = 0;
/**
* @brief Draws a real number according to the given normal distribution
*
* @param mean Mean of the normal distribution
* @param sd Standard deviation of the normal distribution
*/
virtual double normal(double mean, double sd) = 0;
};
/** A random number generator using the C++ standard library.
*
* Caution: reproducibility is not guaranteed across different implementations.
*/
class XBT_PUBLIC StdRandom : public Random {
public:
using Random::Random;
int uniform_int(int min, int max) override;
double uniform_real(double min, double max) override;
double exponential(double lambda) override;
double normal(double mean, double sd) override;
};
/** A reproducible random number generator.
*
* Uses our own implementation of distributions to ensure reproducibility.
*/
class XBT_PUBLIC XbtRandom : public Random {
public:
using Random::Random;
int uniform_int(int min, int max) override;
double uniform_real(double min, double max) override;
double exponential(double lambda) override;
double normal(double mean, double sd) override;
};
/**
* @brief Tells xbt/random to use the ad-hoc distribution implementation.
*/
void set_implem_xbt();
/**
* @brief Tells xbt/random to use the standard library distribution implementation.
*/
void set_implem_std();
/**
* @brief Sets the seed of the Mersenne-Twister RNG
*/
void set_mersenne_seed(int);
/**
* @brief Read the state of the Mersenne-Twister RNG from a file.
*/
bool read_mersenne_state(const std::string& filename);
/**
* @brief Write the state of the Mersenne-Twister RNG to a file.
*/
bool write_mersenne_state(const std::string& filename);
/**
* @brief Draws an integer number uniformly in range [min, max] (min and max included)
*
* @param min Minimum value
* @param max Maximum value
*/
int uniform_int(int min, int max);
/**
* @brief Draws a real number uniformly in range [min, max) (min included, and max excluded)
*
* @param min Minimum value
* @param max Maximum value
*/
double uniform_real(double min, double max);
/**
* @brief Draws a real number according to the given exponential distribution
*
* @param lambda Parameter of the exponential law
*/
double exponential(double lambda);
/**
* @brief Draws a real number according to the given normal distribution
*
* @param mean Mean of the normal distribution
* @param sd Standard deviation of the normal distribution
*/
double normal(double mean, double sd);
} // namespace simgrid::xbt::random
#endif
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