112 lines
3.3 KiB
C++
112 lines
3.3 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* 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
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2016-2017 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef CRUFT_UTIL_RANDOM_HPP
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#define CRUFT_UTIL_RANDOM_HPP
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#include <algorithm>
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#include <array>
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#include <random>
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#include <limits>
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namespace util::random {
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template <typename T>
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struct state_size;
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template <
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class UIntType,
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size_t w, size_t n, size_t m, size_t r,
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UIntType a, size_t u, UIntType d, size_t s,
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UIntType b, size_t t,
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UIntType c, size_t l, UIntType f
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> struct state_size<std::mersenne_twister_engine<UIntType,w,n,m,r,a,u,d,s,b,t,c,l,f>> {
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static constexpr auto value = n * sizeof (UIntType);
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};
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template <typename UIntType, UIntType a, UIntType c, UIntType m>
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struct state_size<std::linear_congruential_engine<UIntType,a,c,m>> {
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static constexpr auto value = sizeof (UIntType);
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};
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template <typename T>
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constexpr auto state_size_v = state_size<T>::value;
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///////////////////////////////////////////////////////////////////////////
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/// return correctly initialised thread-local generator of an unspecified,
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/// but not entirely useless, type. ie, not LCG.
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inline auto&
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generator (void)
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{
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using generator_t = std::default_random_engine;
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static thread_local generator_t gen = [] () {
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std::array<int,state_size_v<generator_t> / 4> seed;
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std::generate (seed.begin (), seed.end (), std::random_device ());
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std::seed_seq seq (seed.begin (), seed.end ());
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return generator_t (seq);
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} ();
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return gen;
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}
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///////////////////////////////////////////////////////////////////////////
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/// select a value uniformly from the range [lo, hi)
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template <typename T>
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std::enable_if_t<std::is_floating_point_v<T>,T>
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uniform (T lo, T hi)
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{
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return std::uniform_real_distribution<T> { lo, hi } (generator ());
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}
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//-------------------------------------------------------------------------
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/// select a value uniformly from the range [lo, hi)
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template <typename T>
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std::enable_if_t<std::is_integral_v<T>,T>
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uniform (T lo, T hi)
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{
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return std::uniform_int_distribution<T> { lo, hi } (generator ());
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}
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///////////////////////////////////////////////////////////////////////////
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template <typename T>
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std::enable_if_t<std::is_integral_v<T>,T>
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uniform (void)
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{
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return uniform (
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std::numeric_limits<T>::min (),
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std::numeric_limits<T>::max ()
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);
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}
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///////////////////////////////////////////////////////////////////////////
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/// choose a value at random from an array
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template <typename T, size_t N>
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T&
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choose (T (&t)[N])
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{
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std::uniform_int_distribution<size_t> dist (0, N - 1);
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return t[dist (generator ())];
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}
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};
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#endif
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