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/*
* bits_count_ones.h
*
* 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.
*
*/
#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
*/
static inline int
ws_count_ones(const guint64 x)
{
guint64 bits = x;
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 (int)((bits * G_GUINT64_CONSTANT(0x0101010101010101)) >> 56);
}
#endif /* __WSUTIL_BITS_COUNT_ONES_H__ */
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