deduplicate code implementing log2p1()

include/libtorrent/aux_/ffs.hpp

@@ -37,7 +37,8 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/aux_/export.hpp"
 #include "libtorrent/span.hpp"
 
-namespace libtorrent { namespace aux {
+namespace libtorrent {
+namespace aux {
 
 	// For a general reference of the problems these routines are about
 	// see http://en.wikipedia.org/wiki/Find_first_set
@@ -61,6 +62,9 @@ namespace libtorrent { namespace aux {
 	// this function statically determines if hardware or software is used
 	// and expect the range to be in big-endian byte order
 	TORRENT_EXTRA_EXPORT int count_trailing_ones(span<std::uint32_t const> buf);
+
+	// returns the index of the most significant set bit.
+	TORRENT_EXTRA_EXPORT int log2p1(std::uint32_t v);
 }}
 
 #endif // TORRENT_FFS_HPP_INCLUDE

src/ffs.cpp

@@ -42,7 +42,28 @@ POSSIBILITY OF SUCH DAMAGE.
 
 #include "libtorrent/aux_/disable_warnings_pop.hpp"
 
-namespace libtorrent { namespace aux {
+namespace libtorrent {
+namespace aux {
+
+	// returns the index of the first set bit.
+	// Use std::log2p1 in C++20
+	int log2p1(std::uint32_t v)
+	{
+// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn
+		static const int MultiplyDeBruijnBitPosition[32] =
+		{
+			0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
+			8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
+		};
+
+		v |= v >> 1; // first round down to one less than a power of 2
+		v |= v >> 2;
+		v |= v >> 4;
+		v |= v >> 8;
+		v |= v >> 16;
+
+		return MultiplyDeBruijnBitPosition[std::uint32_t(v * 0x07C4ACDDU) >> 27];
+	}
 
 	int count_leading_zeros_sw(span<std::uint32_t const> buf)
 	{
@@ -55,23 +76,7 @@ namespace libtorrent { namespace aux {
 		for (int i = 0; i < num; i++)
 		{
 			if (ptr[i] == 0) continue;
-			std::uint32_t v = aux::network_to_host(ptr[i]);
+			return i * 32 + 31 - log2p1(aux::network_to_host(ptr[i]));
-
-			// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious
-			static const int MultiplyDeBruijnBitPosition[32] =
-			{
-				0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
-				8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
-			};
-
-			v |= v >> 1; // first round down to one less than a power of 2
-			v |= v >> 2;
-			v |= v >> 4;
-			v |= v >> 8;
-			v |= v >> 16;
-
-			return i * 32 + 31 - MultiplyDeBruijnBitPosition[
-				static_cast<std::uint32_t>(v * 0x07C4ACDDU) >> 27];
 		}
 
 		return num * 32;

src/session_impl.cpp

@@ -90,6 +90,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/aux_/scope_end.hpp"
 #include "libtorrent/aux_/set_socket_buffer.hpp"
 #include "libtorrent/aux_/generate_peer_id.hpp"
+#include "libtorrent/aux_/ffs.hpp"
 
 #ifndef TORRENT_DISABLE_LOGGING
 
@@ -3510,37 +3511,15 @@ namespace aux {
 		}
 	}
 
-	namespace {
-	// returns the index of the first set bit.
-	int log2(std::uint32_t v)
-	{
-// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn
-		static const int MultiplyDeBruijnBitPosition[32] =
-		{
-			0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
-			8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
-		};
-
-		v |= v >> 1; // first round down to one less than a power of 2
-		v |= v >> 2;
-		v |= v >> 4;
-		v |= v >> 8;
-		v |= v >> 16;
-
-		return MultiplyDeBruijnBitPosition[std::uint32_t(v * 0x07C4ACDDU) >> 27];
-	}
-
-	} // anonymous namespace
-
 	void session_impl::received_buffer(int s)
 	{
-		int index = std::min(log2(std::uint32_t(s >> 3)), 17);
+		int index = std::min(aux::log2p1(std::uint32_t(s >> 3)), 17);
 		m_stats_counters.inc_stats_counter(counters::socket_recv_size3 + index);
 	}
 
 	void session_impl::sent_buffer(int s)
 	{
-		int index = std::min(log2(std::uint32_t(s >> 3)), 17);
+		int index = std::min(aux::log2p1(std::uint32_t(s >> 3)), 17);
 		m_stats_counters.inc_stats_counter(counters::socket_send_size3 + index);
 	}