Make lowest_bit() more efficient

As a nice bonus, this also removes the dependency on Boost.Integer.

CMakeLists.txt

@@ -46,7 +46,7 @@ if (BOOST_DYNAMIC_BITSET_IS_ROOT)
 
     # If BOOST_SRC_DIR is valid, fallback to find_package
     set(CMAKE_FOLDER Dependencies)
-    set(BOOST_INCLUDE_LIBRARIES assert config container_hash core integer move throw_exception)
+    set(BOOST_INCLUDE_LIBRARIES assert config container_hash core move throw_exception)
     set(BOOST_EXCLUDE_LIBRARIES dynamic_bitset)
     set(PREV_BUILD_TESTING ${BUILD_TESTING})
     set(BUILD_TESTING OFF CACHE BOOL "Build the tests." FORCE)
@@ -62,7 +62,6 @@ target_link_libraries(boost_dynamic_bitset
     Boost::config
     Boost::container_hash
     Boost::core
-    Boost::integer
     Boost::move
     Boost::throw_exception
 )

build.jam

@@ -10,7 +10,6 @@ constant boost_dependencies :
     /boost/config//boost_config
     /boost/container_hash//boost_container_hash
     /boost/core//boost_core
-    /boost/integer//boost_integer
     /boost/move//boost_move
     /boost/throw_exception//boost_throw_exception ;
 

include/boost/dynamic_bitset/detail/lowest_bit.hpp

@@ -15,7 +15,8 @@
 #define BOOST_LOWEST_BIT_HPP_GP_20030301
 
 #include "boost/assert.hpp"
-#include "boost/integer/integer_log2.hpp"
+#include "boost/core/bit.hpp"
+#include <type_traits>
 
 namespace boost {
 namespace detail {
@@ -26,10 +27,7 @@ lowest_bit( T x )
 {
     BOOST_ASSERT( x >= 1 );
 
-    // Clear all the bits that are set except the rightmost one,
-    // then calculate the logarithm to base 2.
-    //
-    return boost::integer_log2< T >( x - ( x & ( x - 1 ) ) );
+    return boost::core::countr_zero( static_cast< typename std::make_unsigned< T >::type >( x ) );
 }
 
 }