williamr@2: // -------------------------------------
williamr@2: // lowest_bit.hpp
williamr@2: //
williamr@2: //           Position of the lowest bit 'on'
williamr@2: //
williamr@2: //       (C) Copyright Gennaro Prota 2003 - 2004.
williamr@2: //
williamr@2: // Distributed under the Boost Software License, Version 1.0.
williamr@2: //    (See accompanying file LICENSE_1_0.txt or copy at
williamr@2: //          http://www.boost.org/LICENSE_1_0.txt)
williamr@2: //
williamr@2: // ------------------------------------------------------
williamr@2: 
williamr@2: #ifndef BOOST_LOWEST_BIT_HPP_GP_20030301
williamr@2: #define BOOST_LOWEST_BIT_HPP_GP_20030301
williamr@2: 
williamr@2: #include <cassert>
williamr@2: #include "boost/pending/integer_log2.hpp"
williamr@2: 
williamr@2: 
williamr@2: namespace boost {
williamr@2: 
williamr@2:     template <typename T>
williamr@2:     int lowest_bit(T x) {
williamr@2: 
williamr@2:         assert(x >= 1); // PRE
williamr@2: 
williamr@2:         // clear all bits on except the rightmost one,
williamr@2:         // then calculate the logarithm base 2
williamr@2:         //
williamr@2:         return boost::integer_log2<T>( x - ( x & (x-1) ) );
williamr@2: 
williamr@2:     }
williamr@2: 
williamr@2: 
williamr@2: }
williamr@2: 
williamr@2: 
williamr@2: #endif // include guard