wmem: allow wmem_destroy_list to ignore a NULL list.

[metze/wireshark/wip.git] / wsutil / bits_count_ones.h

diff --git a/wsutil/bits_count_ones.h b/wsutil/bits_count_ones.h
index 3d88d52fa91854845e5b4450896bb7fbeda6f956..97f8e50226d009e7665bfa2273a7248c3ca3adaa 100644 (file)
--- a/wsutil/bits_count_ones.h
+++ b/wsutil/bits_count_ones.h
@@ -1,53 +1,52 @@
 /*
  * bits_count_ones.h
  *
- * $Id$
- *
  * 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.
- *
+ * SPDX-License-Identifier: GPL-2.0-or-later
  */
 
 #ifndef __WSUTIL_BITS_COUNT_ONES_H__
 #define __WSUTIL_BITS_COUNT_ONES_H__
 
-#include "config.h"
-
 #include <glib.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
+ * the number of bits set in an integer:
+ *
+ *     http://playingwithpointers.com/swar.html
+ *
+ * See
+ *
+ *     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36041
+ *     https://danluu.com/assembly-intrinsics/
+ *
+ * for discussions of various forms of population-counting code on x86.
+ *
+ * See
+ *
+ *     https://msdn.microsoft.com/en-us/library/bb385231.aspx
+ *
+ * for MSVC's population count intrinsics.
+ *
+ * Note that not all x86 processors support the POPCOUNT instruction.
+ *
+ * Other CPUs may have population count instructions as well.
  */
 
 static inline int
-ws_count_ones(const guint32 x)
+ws_count_ones(const guint64 x)
 {
-       int bits = x;
+       guint64 bits = x;
 
-       bits = bits - ((bits >> 1) & 0x55555555);
-       bits = (bits & 0x33333333) + ((bits >> 2) & 0x33333333);
-       bits = (bits + (bits >> 4)) & 0x0F0F0F0F;
+       bits = bits - ((bits >> 1) & G_GUINT64_CONSTANT(0x5555555555555555));
+       bits = (bits & G_GUINT64_CONSTANT(0x3333333333333333)) + ((bits >> 2) & G_GUINT64_CONSTANT(0x3333333333333333));
+       bits = (bits + (bits >> 4)) & G_GUINT64_CONSTANT(0x0F0F0F0F0F0F0F0F);
 
-       return (bits * 0x01010101) >> 24;
+       return (int)((bits * G_GUINT64_CONSTANT(0x0101010101010101)) >> 56);
 }
 
 #endif /* __WSUTIL_BITS_COUNT_ONES_H__ */