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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/***************************************************************************
* random.cc
*
* Wed Mar 23 19:17:24 CET 2016
* Copyright 2016 André Nusser
* andre.nusser@googlemail.com
****************************************************************************/
/*
* This file is part of DrumGizmo.
*
* DrumGizmo is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* DrumGizmo is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with DrumGizmo; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
#include "random.h"
#include <chrono>
#include <type_traits>
#include <cmath>
Random::Random()
: Random(std::chrono::system_clock::now().time_since_epoch().count())
{
}
Random::Random(unsigned int seed)
{
setSeed(seed);
}
void Random::setSeed(unsigned int seed)
{
generator.seed(seed);
}
int Random::intInRange(int lower_bound, int upper_bound)
{
auto generate = [this]()
{
return (int)generator() - generator.min();
};
const int in_range = generator.max() - generator.min();
const int out_range = upper_bound - lower_bound;
int rand;
// scale in_range DOWN to out_range.
// (see: http://www.azillionmonkeys.com/qed/random.html)
if (in_range > out_range)
{
const int rand_inv_range = in_range / (out_range + 1);
do
{
rand = generate();
}
while (rand >= (out_range + 1) * rand_inv_range);
rand = lower_bound + rand/rand_inv_range;
}
// scale in_range UP to out_range.
// (see: http://stackoverflow.com/a/30738381)
else if (in_range < out_range)
{
int scale = out_range / (in_range + 1);
do
{
rand = generate() + intInRange(0, scale) * (in_range + 1);
}
while (rand < lower_bound && rand > upper_bound);
rand = lower_bound + rand;
}
// naive case
else
{
rand = lower_bound + generate();
}
return rand;
}
float Random::floatInRange(float lower_bound, float upper_bound)
{
return generateFloat() * (upper_bound - lower_bound) + lower_bound;
}
// For details regarding the algorithm see:
// https://en.wikipedia.org/wiki/Marsaglia_polar_method
float Random::normalDistribution(float mean, float stddev)
{
if (has_saved_value)
{
has_saved_value = false;
return saved_value * stddev + mean;
}
else
{
float u, v, s;
do
{
u = 2.0f*generateFloat() - 1;
v = 2.0f*generateFloat() - 1;
s = (u * u) + (v * v);
}
while (s > 1.0f || s == 0.0f);
s = std::sqrt(-2*std::log(s) / s);
saved_value = u * s;
has_saved_value = true;
return mean + stddev * (v * s);
}
}
float Random::generateFloat()
{
return std::generate_canonical<float,
std::numeric_limits<float>::digits,
decltype(generator)>(generator);
}
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