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