boost/pending/lowest_bit.hpp

   1 // -----------------------------------------------------------
   2 // lowest_bit.hpp
   3 //
   4 //           Position of the lowest bit 'on'
   5 //
   6 //         Copyright (c) 2003-2004, 2008 Gennaro Prota
   7 //
   8 // Distributed under the Boost Software License, Version 1.0.
   9 //    (See accompanying file LICENSE_1_0.txt or copy at
  10 //          http://www.boost.org/LICENSE_1_0.txt)
  11 //
  12 // -----------------------------------------------------------
  13
  14 #ifndef BOOST_LOWEST_BIT_HPP_GP_20030301
  15 #define BOOST_LOWEST_BIT_HPP_GP_20030301
  16
  17 #include <assert.h>
  18 #include "boost/pending/integer_log2.hpp"
  19
  20
  21 namespace boost {
  22
  23     template <typename T>
  24     int lowest_bit(T x) {
  25
  26         assert(x >= 1); // PRE
  27
  28         // clear all bits on except the rightmost one,
  29         // then calculate the logarithm base 2
  30         //
  31         return boost::integer_log2<T>( x - ( x & (x-1) ) );
  32
  33     }
  34
  35
  36 }
  37
  38
  39 #endif // include guard