82 lines
2.0 KiB
C++
82 lines
2.0 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2015-2019 Danny Robson <danny@nerdcruft.net>
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*/
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#include "xorshift.hpp"
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#include "../debug/assert.hpp"
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#include <cstdint>
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using cruft::rand::xorshift;
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///////////////////////////////////////////////////////////////////////////////
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template <typename T>
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xorshift<T>::xorshift (T seed):
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m_state (seed)
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{
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if (!m_state)
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throw std::invalid_argument ("xorshift seed must not be zero");
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}
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///////////////////////////////////////////////////////////////////////////////
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// setup the constants a, b, and c. we use the values from the example
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// generators provided in Marsaglia's paper.
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template <typename T>
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struct constants;
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//-----------------------------------------------------------------------------
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template <>
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struct constants<uint32_t>
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{
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static constexpr uint32_t a = 13u;
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static constexpr uint32_t b = 17u;
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static constexpr uint32_t c = 5u;
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};
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//-----------------------------------------------------------------------------
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template <>
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struct constants<uint64_t>
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{
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static constexpr uint64_t a = 13u;
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static constexpr uint64_t b = 7u;
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static constexpr uint64_t c = 17u;
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};
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///////////////////////////////////////////////////////////////////////////////
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template <typename T>
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typename xorshift<T>::result_type
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xorshift<T>::operator() (void)
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{
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m_state ^= m_state >> constants<T>::a;
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m_state ^= m_state << constants<T>::b;
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m_state ^= m_state >> constants<T>::c;
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CHECK_NEZ (m_state);
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return m_state;
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}
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///////////////////////////////////////////////////////////////////////////////
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template <typename T>
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void
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xorshift<T>::discard (unsigned count)
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{
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while (count--)
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(*this)();
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}
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///////////////////////////////////////////////////////////////////////////////
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template struct cruft::rand::xorshift<uint32_t>;
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template struct cruft::rand::xorshift<uint64_t>;
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