libcruft-util/random.hpp

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/*
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* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
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*
* Copyright 2016-2017 Danny Robson <danny@nerdcruft.net>
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*/
#ifndef CRUFT_UTIL_RANDOM_HPP
#define CRUFT_UTIL_RANDOM_HPP
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#include <algorithm>
#include <random>
#include <limits>
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namespace util::random {
///////////////////////////////////////////////////////////////////////////
/// return correctly initialised thread-local generator of an unspecified,
/// but not entirely useless, type. ie, not LCG.
inline auto&
generator (void)
{
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static thread_local std::default_random_engine gen { std::random_device {}() };
return gen;
}
///////////////////////////////////////////////////////////////////////////
/// select a value uniformly from the range [lo, hi)
template <typename T>
std::enable_if_t<std::is_floating_point_v<T>,T>
uniform (T lo, T hi)
{
return std::uniform_real_distribution<T> { lo, hi } (generator ());
}
//-------------------------------------------------------------------------
/// select a value uniformly from the range [lo, hi)
template <typename T>
std::enable_if_t<std::is_integral_v<T>,T>
uniform (T lo, T hi)
{
return std::uniform_int_distribution<T> { lo, hi } (generator ());
}
///////////////////////////////////////////////////////////////////////////
template <typename T>
std::enable_if_t<std::is_integral_v<T>,T>
uniform (void)
{
return uniform (
std::numeric_limits<T>::min (),
std::numeric_limits<T>::max ()
);
}
///////////////////////////////////////////////////////////////////////////
/// choose a value at random from an array
template <typename T, size_t N>
T&
choose (T (&t)[N])
{
std::uniform_int_distribution<size_t> dist (0, N - 1);
return t[dist (generator ())];
}
};
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#endif