1 files changed, 49 insertions, 0 deletions
diff --git a/wsutil/swar.c b/wsutil/swar.c
new file mode 100644
index 0000000000..c784ea42f9
--- /dev/null
+++ b/wsutil/swar.c
@@ -0,0 +1,49 @@
+/*
+ *  swar.c
+ *
+ * $Id$
+ *
+ * Wireshark - Network traffic analyzer
+ * By Gerald Combs <gerald@wireshark.org>
+ * Copyright 1998 Gerald Combs
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include "config.h"
+
+#include <glib.h>
+
+#include "swar.h"
+
+/*
+ * The variable-precision SWAR algorithm is an interesting way to count 
+ * the number of bits set in an integer. While its performance is very 
+ * good (two times faster than gcc's __builtin_popcount [1] and 
+ * 16 instructions when compiled with gcc -O3)
+ * http://playingwithpointers.com/swar.html
+ */
+
+int swar_count_bits(const guint32 bitmask)
+{
+	int bits = bitmask;
+
+	bits = bits - ((bits >> 1) & 0x55555555);
+	bits = (bits & 0x33333333) + ((bits >> 2) & 0x33333333);
+	bits = (bits + (bits >> 4)) & 0x0F0F0F0F;
+
+	return (bits * 0x01010101) >> 24;
+}