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/*
* bitz_ctz.h
*
* Wireshark - Network traffic analyzer
* By Gerald Combs <gerald@wireshark.org>
* Copyright 1998 Gerald Combs
*
* SPDX-License-Identifier: GPL-2.0-or-later
*/
#ifndef __WSUTIL_BITS_CTZ_H__
#define __WSUTIL_BITS_CTZ_H__
#include <glib.h>
/* ws_ctz == trailing zeros == position of lowest set bit [0..63] */
/* ws_ilog2 == position of highest set bit == 63 - leading zeros [0..63] */
/* The return value of both ws_ctz and ws_ilog2 is undefined for x == 0 */
#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
static inline int
ws_ctz(guint64 x)
{
return __builtin_ctzll(x);
}
static inline int
ws_ilog2(guint64 x)
{
return 63 - __builtin_clzll(x);
}
#else
static inline int
__ws_ctz32(guint32 x)
{
/* From http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup */
static const guint8 table[32] = {
0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
};
return table[((guint32)((x & -(gint32)x) * 0x077CB531U)) >> 27];
}
static inline int
ws_ctz(guint64 x)
{
guint32 hi = x >> 32;
guint32 lo = (guint32) x;
if (lo == 0)
return 32 + __ws_ctz32(hi);
else
return __ws_ctz32(lo);
}
static inline int
__ws_ilog2_32(guint32 x)
{
/* From http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn */
static const guint8 table[32] = {
0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
};
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
return table[((guint32)(x * 0x07C4ACDDU)) >> 27];
}
static inline int
ws_ilog2(guint64 x)
{
guint32 hi = x >> 32;
guint32 lo = (guint32) x;
if (hi == 0)
return __ws_ilog2_32(lo);
else
return 32 + __ws_ilog2_32(hi);
}
#endif
#endif /* __WSUTIL_BITS_CTZ_H__ */
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