Chris@16: /* boost random/detail/integer_log2.hpp header file
Chris@16:  *
Chris@16:  * Copyright Steven Watanabe 2011
Chris@16:  * Distributed under the Boost Software License, Version 1.0. (See
Chris@16:  * accompanying file LICENSE_1_0.txt or copy at
Chris@16:  * http://www.boost.org/LICENSE_1_0.txt)
Chris@16:  *
Chris@16:  * See http://www.boost.org for most recent version including documentation.
Chris@16:  *
Chris@101:  * $Id$
Chris@16:  *
Chris@16:  */
Chris@16: 
Chris@16: #ifndef BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP
Chris@16: #define BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP
Chris@16: 
Chris@16: #include <boost/config.hpp>
Chris@16: #include <boost/limits.hpp>
Chris@16: #include <boost/pending/integer_log2.hpp>
Chris@16: 
Chris@16: namespace boost {
Chris@16: namespace random {
Chris@16: namespace detail {
Chris@16: 
Chris@16: #if !defined(BOOST_NO_CXX11_CONSTEXPR)
Chris@16: #define BOOST_RANDOM_DETAIL_CONSTEXPR constexpr
Chris@16: #elif defined(BOOST_MSVC)
Chris@16: #define BOOST_RANDOM_DETAIL_CONSTEXPR __forceinline
Chris@16: #elif defined(__GNUC__) && __GNUC__ >= 4
Chris@101: #define BOOST_RANDOM_DETAIL_CONSTEXPR inline __attribute__((__const__)) __attribute__((__always_inline__))
Chris@16: #else
Chris@16: #define BOOST_RANDOM_DETAIL_CONSTEXPR inline
Chris@16: #endif
Chris@16: 
Chris@16: template<int Shift>
Chris@16: struct integer_log2_impl
Chris@16: {
Chris@16: #if defined(BOOST_NO_CXX11_CONSTEXPR)
Chris@16:     template<class T>
Chris@16:     BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum)
Chris@16:     {
Chris@16:         int update = ((t >> Shift) != 0) * Shift;
Chris@16:         return integer_log2_impl<Shift / 2>::apply(t >> update, accum + update);
Chris@16:     }
Chris@16: #else
Chris@16:     template<class T>
Chris@16:     BOOST_RANDOM_DETAIL_CONSTEXPR static int apply2(T t, int accum, int update)
Chris@16:     {
Chris@16:         return integer_log2_impl<Shift / 2>::apply(t >> update, accum + update);
Chris@16:     }
Chris@16: 
Chris@16:     template<class T>
Chris@16:     BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum)
Chris@16:     {
Chris@16:         return apply2(t, accum, ((t >> Shift) != 0) * Shift);
Chris@16:     }
Chris@16: #endif
Chris@16: };
Chris@16: 
Chris@16: template<>
Chris@16: struct integer_log2_impl<1>
Chris@16: {
Chris@16:     template<class T>
Chris@16:     BOOST_RANDOM_DETAIL_CONSTEXPR static int apply(T t, int accum)
Chris@16:     {
Chris@16:         return int(t >> 1) + accum;
Chris@16:     }
Chris@16: };
Chris@16: 
Chris@16: template<class T>
Chris@16: BOOST_RANDOM_DETAIL_CONSTEXPR int integer_log2(T t)
Chris@16: {
Chris@16:     return integer_log2_impl<
Chris@16:         ::boost::detail::max_pow2_less<
Chris@16:             ::std::numeric_limits<T>::digits, 4
Chris@16:         >::value
Chris@16:     >::apply(t, 0);
Chris@16: }
Chris@16: 
Chris@16: } // namespace detail
Chris@16: } // namespace random
Chris@16: } // namespace boost
Chris@16: 
Chris@16: #endif // BOOST_RANDOM_DETAIL_INTEGER_LOG2_HPP