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