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