85 lines
2.2 KiB
C++
85 lines
2.2 KiB
C++
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/* boost random/detail/integer_log2.hpp header file
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*
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* Copyright Steven Watanabe 2011
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* Distributed under the Boost Software License, Version 1.0. (See
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* accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* See http://www.boost.org for most recent version including documentation.
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*
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* $Id$
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*
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*/
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#ifndef BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP
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#define BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP
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#include <boost/config.hpp>
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#include <boost/limits.hpp>
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#include <boost/pending/integer_log2.hpp>
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namespace boost {
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namespace random {
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namespace detail {
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#if !defined(BOOST_NO_CXX11_CONSTEXPR)
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#define BOOST_RANDOM_DETAIL_CONSTEXPR constexpr
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#elif defined(BOOST_MSVC)
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#define BOOST_RANDOM_DETAIL_CONSTEXPR __forceinline
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#elif defined(__GNUC__) && __GNUC__ >= 4
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#define BOOST_RANDOM_DETAIL_CONSTEXPR inline __attribute__((__const__)) __attribute__((__always_inline__))
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#else
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#define BOOST_RANDOM_DETAIL_CONSTEXPR inline
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#endif
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template<int Shift>
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struct integer_log2_impl
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{
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#if defined(BOOST_NO_CXX11_CONSTEXPR)
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template<class T>
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BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum)
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{
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int update = ((t >> Shift) != 0) * Shift;
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return integer_log2_impl<Shift / 2>::apply(t >> update, accum + update);
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}
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#else
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template<class T>
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BOOST_RANDOM_DETAIL_CONSTEXPR static int apply2(T t, int accum, int update)
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{
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return integer_log2_impl<Shift / 2>::apply(t >> update, accum + update);
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}
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template<class T>
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BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum)
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{
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return apply2(t, accum, ((t >> Shift) != 0) * Shift);
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}
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#endif
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};
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template<>
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struct integer_log2_impl<1>
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{
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template<class T>
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BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum)
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{
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return int(t >> 1) + accum;
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}
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};
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template<class T>
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BOOST_RANDOM_DETAIL_CONSTEXPR int integer_log2(T t)
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{
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return integer_log2_impl<
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::boost::detail::max_pow2_less<
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::std::numeric_limits<T>::digits, 4
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>::value
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>::apply(t, 0);
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}
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} // namespace detail
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} // namespace random
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} // namespace boost
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#endif // BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP
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