blob: c784ea42f988e31ee09220c5196c32b21b1d59a7 (
plain)
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
|
/*
* 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;
}
|
