From ed2f5281fe7b9ca6bff233cfcbfbf7fbcc31157e Mon Sep 17 00:00:00 2001
From: Gennaro Prota <gennaro.prota@gmail.com>
Date: Wed, 10 Sep 2025 18:57:11 +0200
Subject: [PATCH] Make lowest_bit() more efficient

As a nice bonus, this also removes the dependency on Boost.Integer.
---
 CMakeLists.txt                                     | 3 +--
 build.jam                                          | 1 -
 include/boost/dynamic_bitset/detail/lowest_bit.hpp | 8 +++-----
 3 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e31af44..261c8ee 100644
--- a/CMakeLists.txt
+++ b/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
 )
diff --git a/build.jam b/build.jam
index 67e5e65..a5949b5 100644
--- a/build.jam
+++ b/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 ;
 
diff --git a/include/boost/dynamic_bitset/detail/lowest_bit.hpp b/include/boost/dynamic_bitset/detail/lowest_bit.hpp
index 79f7225..bd2f947 100644
--- a/include/boost/dynamic_bitset/detail/lowest_bit.hpp
+++ b/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 ) );
 }
 
 }