dynamic_bitset/detail/lowest_bit.hpp

0001 // -----------------------------------------------------------
0002 // lowest_bit.hpp
0003 //
0004 //           Position of the lowest bit 'on'
0005 //
0006 //         Copyright (c) 2003-2004, 2008 Gennaro Prota
0007 //
0008 // Distributed under the Boost Software License, Version 1.0.
0009 //    (See accompanying file LICENSE_1_0.txt or copy at
0010 //          http://www.boost.org/LICENSE_1_0.txt)
0011 //
0012 // -----------------------------------------------------------
0013
0014 #ifndef BOOST_LOWEST_BIT_HPP_GP_20030301
0015 #define BOOST_LOWEST_BIT_HPP_GP_20030301
0016
0017 #include "boost/integer/integer_log2.hpp"
0018 #include "boost/assert.hpp"
0019
0020 namespace boost {
0021 namespace detail {
0022
0023     template <typename T>
0024     int lowest_bit(T x) {
0025
0026         BOOST_ASSERT(x >= 1); // PRE
0027
0028         // clear all bits on except the rightmost one,
0029         // then calculate the logarithm base 2
0030         //
0031         return boost::integer_log2<T>( x - ( x & (x-1) ) );
0032
0033     }
0034
0035 }
0036 }
0037
0038
0039 #endif // include guard