From 919b98d425cb0251806a2c24eba05e38c8c74c3d Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Tue, 29 Dec 2020 02:06:56 +0200
Subject: [PATCH] Use __builtin_popcount

---
 include/boost/core/bit.hpp | 42 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/include/boost/core/bit.hpp b/include/boost/core/bit.hpp
index 81898d8..dd85b2a 100644
--- a/include/boost/core/bit.hpp
+++ b/include/boost/core/bit.hpp
@@ -327,6 +327,46 @@ BOOST_CONSTEXPR int countr_one( T x ) BOOST_NOEXCEPT
 
 // popcount
 
+#if defined(__GNUC__) || defined(__clang__)
+
+namespace detail
+{
+
+BOOST_CONSTEXPR inline int popcount_impl( unsigned char x ) BOOST_NOEXCEPT
+{
+    return __builtin_popcount( x );
+}
+
+BOOST_CONSTEXPR inline int popcount_impl( unsigned short x ) BOOST_NOEXCEPT
+{
+    return __builtin_popcount( x );
+}
+
+BOOST_CONSTEXPR inline int popcount_impl( unsigned int x ) BOOST_NOEXCEPT
+{
+    return __builtin_popcount( x );
+}
+
+BOOST_CONSTEXPR inline int popcount_impl( unsigned long x ) BOOST_NOEXCEPT
+{
+    return __builtin_popcountl( x );
+}
+
+BOOST_CONSTEXPR inline int popcount_impl( unsigned long long x ) BOOST_NOEXCEPT
+{
+    return __builtin_popcountll( x );
+}
+
+} // namespace detail
+
+template<class T>
+BOOST_CONSTEXPR int popcount( T x ) BOOST_NOEXCEPT
+{
+    return boost::core::detail::popcount_impl( x );
+}
+
+#else // defined(__GNUC__) || defined(__clang__)
+
 namespace detail
 {
 
@@ -365,6 +405,8 @@ BOOST_CXX14_CONSTEXPR int popcount( T x ) BOOST_NOEXCEPT
     }
 }
 
+#endif // defined(__GNUC__) || defined(__clang__)
+
 // rotating
 
 template<class T>