/usr/include/wireshark/wsutil/bits_count_ones.h is in libwsutil-dev 1.12.1+g01b65bf-4+deb8u14.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 | /*
* 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 guint32 x)
{
int bits = x;
bits = bits - ((bits >> 1) & 0x55555555);
bits = (bits & 0x33333333) + ((bits >> 2) & 0x33333333);
bits = (bits + (bits >> 4)) & 0x0F0F0F0F;
return (bits * 0x01010101) >> 24;
}
#endif /* __WSUTIL_BITS_COUNT_ONES_H__ */
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