1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
|
/*
* Copyright 2009, Google Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
// This file defines some bit utilities.
#ifndef O3D_BASE_CROSS_BITS_H_
#define O3D_BASE_CROSS_BITS_H_
#include "base/logging.h"
namespace o3d {
namespace base {
namespace bits {
// Returns the integer i such as 2^i <= n < 2^(i+1)
static inline int Log2Floor(unsigned int n) {
if (n == 0)
return -1;
int log = 0;
unsigned int value = n;
for (int i = 4; i >= 0; --i) {
int shift = (1 << i);
unsigned int x = value >> shift;
if (x != 0) {
value = x;
log += shift;
}
}
DCHECK_EQ(value, 1u);
return log;
}
// Returns the integer i such as 2^(i-1) < n <= 2^i
static inline int Log2Ceiling(unsigned int n) {
if (n == 0) {
return -1;
} else {
// Log2Floor returns -1 for 0, so the following works correctly for n=1.
return 1 + Log2Floor(n - 1);
}
}
} // namespace bits
} // namespace base
} // namespace o3d
#endif // O3D_BASE_CROSS_BITS_H_
|
