boost/integer/static_log2.hpp
// Boost integer/static_log2.hpp header file -------------------------------// // (C) Copyright Daryle Walker 2001. Permission to copy, use, modify, sell and // distribute this software is granted provided this copyright notice appears // in all copies. This software is provided "as is" without express or // implied warranty, and with no claim as to its suitability for any purpose. // See http://www.boost.org for updates, documentation, and revision history. #ifndef BOOST_INTEGER_STATIC_LOG2_HPP #define BOOST_INTEGER_STATIC_LOG2_HPP #include <boost/integer_fwd.hpp> // self include #include <boost/config.hpp> // for BOOST_STATIC_CONSTANT, etc. #include <boost/limits.hpp> // for std::numeric_limits #ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION #include <boost/pending/ct_if.hpp> // for boost::ct_if<> #endif namespace boost { // Implementation details --------------------------------------------------// namespace detail { // Forward declarations template < unsigned long Val, int Place = 0, int Index = std::numeric_limits<unsigned long>::digits > struct static_log2_helper_t; #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION template < unsigned long Val, int Place > struct static_log2_helper_t< Val, Place, 1 >; #else template < int Place > struct static_log2_helper_final_step; template < unsigned long Val, int Place = 0, int Index = std::numeric_limits<unsigned long>::digits > struct static_log2_helper_nopts_t; #endif // Recursively build the logarithm by examining the upper bits template < unsigned long Val, int Place, int Index > struct static_log2_helper_t { private: BOOST_STATIC_CONSTANT( int, half_place = Index / 2 ); BOOST_STATIC_CONSTANT( unsigned long, lower_mask = (1ul << half_place) - 1ul ); BOOST_STATIC_CONSTANT( unsigned long, upper_mask = ~lower_mask ); BOOST_STATIC_CONSTANT( bool, do_shift = (Val & upper_mask) != 0ul ); BOOST_STATIC_CONSTANT( unsigned long, new_val = do_shift ? (Val >> half_place) : Val ); BOOST_STATIC_CONSTANT( int, new_place = do_shift ? (Place + half_place) : Place ); BOOST_STATIC_CONSTANT( int, new_index = Index - half_place ); #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION typedef static_log2_helper_t<new_val, new_place, new_index> next_step_type; #else typedef static_log2_helper_nopts_t<new_val, new_place, new_index> next_step_type; #endif public: BOOST_STATIC_CONSTANT( int, value = next_step_type::value ); }; // boost::detail::static_log2_helper_t // Non-recursive case #ifndef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION template < unsigned long Val, int Place > struct static_log2_helper_t< Val, Place, 1 > { public: BOOST_STATIC_CONSTANT( int, value = Place ); }; // boost::detail::static_log2_helper_t #else template < int Place > struct static_log2_helper_final_step { public: BOOST_STATIC_CONSTANT( int, value = Place ); }; // boost::detail::static_log2_helper_final_step template < unsigned long Val, int Place, int Index > struct static_log2_helper_nopts_t { private: typedef static_log2_helper_t<Val, Place, Index> recursive_step_type; typedef static_log2_helper_final_step<Place> final_step_type; typedef typename ct_if<( Index != 1 ), recursive_step_type, final_step_type>::type next_step_type; public: BOOST_STATIC_CONSTANT( int, value = next_step_type::value ); }; // boost::detail::static_log2_helper_nopts_t #endif } // namespace detail // Compile-time log-base-2 evaluator class declaration ---------------------// template < unsigned long Value > struct static_log2 { BOOST_STATIC_CONSTANT( int, value = detail::static_log2_helper_t<Value>::value ); }; template < > struct static_log2< 0ul > { // The logarithm of zero is undefined. }; } // namespace boost #endif // BOOST_INTEGER_STATIC_LOG2_HPP