Wireshark  2.9.0-477-g68ec514b
The Wireshark network protocol analyzer
bits_ctz.h
1 /*
2  * bitz_ctz.h
3  *
4  * Wireshark - Network traffic analyzer
5  * By Gerald Combs <gerald@wireshark.org>
6  * Copyright 1998 Gerald Combs
7  *
8  * SPDX-License-Identifier: GPL-2.0-or-later
9  */
10 
11 #ifndef __WSUTIL_BITS_CTZ_H__
12 #define __WSUTIL_BITS_CTZ_H__
13 
14 #include <glib.h>
15 
16 /* ws_ctz == trailing zeros == position of lowest set bit [0..63] */
17 /* ws_ilog2 == position of highest set bit == 63 - leading zeros [0..63] */
18 
19 /* The return value of both ws_ctz and ws_ilog2 is undefined for x == 0 */
20 
21 #if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
22 
23 static inline int
24 ws_ctz(guint64 x)
25 {
26  return __builtin_ctzll(x);
27 }
28 
29 static inline int
30 ws_ilog2(guint64 x)
31 {
32  return 63 - __builtin_clzll(x);
33 }
34 
35 #else
36 
37 static inline int
38 __ws_ctz32(guint32 x)
39 {
40  /* From http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup */
41  static const guint8 table[32] = {
42  0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
43  31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
44  };
45 
46  return table[((guint32)((x & -(gint32)x) * 0x077CB531U)) >> 27];
47 }
48 
49 static inline int
50 ws_ctz(guint64 x)
51 {
52  guint32 hi = x >> 32;
53  guint32 lo = (guint32) x;
54 
55  if (lo == 0)
56  return 32 + __ws_ctz32(hi);
57  else
58  return __ws_ctz32(lo);
59 }
60 
61 static inline int
62 __ws_ilog2_32(guint32 x)
63 {
64  /* From http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn */
65  static const guint8 table[32] = {
66  0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
67  8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
68  };
69 
70  x |= x >> 1;
71  x |= x >> 2;
72  x |= x >> 4;
73  x |= x >> 8;
74  x |= x >> 16;
75 
76  return table[((guint32)(x * 0x07C4ACDDU)) >> 27];
77 }
78 
79 static inline int
80 ws_ilog2(guint64 x)
81 {
82  guint32 hi = x >> 32;
83  guint32 lo = (guint32) x;
84 
85  if (hi == 0)
86  return __ws_ilog2_32(lo);
87  else
88  return 32 + __ws_ilog2_32(hi);
89 }
90 
91 #endif
92 
93 #endif /* __WSUTIL_BITS_CTZ_H__ */