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/*
* bits_count_ones.h
*
* Wireshark - Network traffic analyzer
* By Gerald Combs <gerald@wireshark.org>
* Copyright 1998 Gerald Combs
*
* SPDX-License-Identifier: GPL-2.0+
*/
#ifndef __WSUTIL_BITS_COUNT_ONES_H__
#define __WSUTIL_BITS_COUNT_ONES_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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