libcruft-util/rand/xorshift.cpp

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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
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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.
*
* Copyright 2015-2016 Danny Robson <danny@nerdcruft.net>
*/
#include "./xorshift.hpp"
#include "../debug.hpp"
#include <cstdint>
using util::rand::xorshift;
///////////////////////////////////////////////////////////////////////////////
template <typename T>
xorshift<T>::xorshift (T seed):
m_state (seed)
{
if (!m_state)
throw std::invalid_argument ("xorshift seed must not be zero");
}
///////////////////////////////////////////////////////////////////////////////
// setup the constants a, b, and c. we use the values from the example
// generators provided in Marsaglia's paper.
template <typename T>
struct constants;
//-----------------------------------------------------------------------------
template <>
struct constants<uint32_t>
{
static constexpr uint32_t a = 13u;
static constexpr uint32_t b = 17u;
static constexpr uint32_t c = 5u;
};
//-----------------------------------------------------------------------------
template <>
struct constants<uint64_t>
{
static constexpr uint64_t a = 13u;
static constexpr uint64_t b = 7u;
static constexpr uint64_t c = 17u;
};
///////////////////////////////////////////////////////////////////////////////
template <typename T>
typename xorshift<T>::result_type
xorshift<T>::operator() (void)
{
m_state ^= m_state >> constants<T>::a;
m_state ^= m_state << constants<T>::b;
m_state ^= m_state >> constants<T>::c;
CHECK_NEZ (m_state);
return m_state;
};
///////////////////////////////////////////////////////////////////////////////
template <typename T>
typename xorshift<T>::result_type
xorshift<T>::min (void)
{
return 1u;
}
//-----------------------------------------------------------------------------
template <typename T>
typename xorshift<T>::result_type
xorshift<T>::max (void)
{
return std::numeric_limits<T>::max ();
}
///////////////////////////////////////////////////////////////////////////////
template <typename T>
void
xorshift<T>::discard (unsigned count)
{
while (count--)
(*this)();
}
///////////////////////////////////////////////////////////////////////////////
template struct util::rand::xorshift<uint32_t>;
template struct util::rand::xorshift<uint64_t>;