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apatrick@google.com0265b732009-11-19 08:08:39 +09001// Copyright (c) 2009 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// This file defines some bit utilities.
6
7#ifndef BASE_BITS_H_
8#define BASE_BITS_H_
apatrick@google.com0265b732009-11-19 08:08:39 +09009
10#include "base/basictypes.h"
11#include "base/logging.h"
12
13namespace base {
14namespace bits {
15
16// Returns the integer i such as 2^i <= n < 2^(i+1)
17inline int Log2Floor(uint32 n) {
18 if (n == 0)
19 return -1;
20 int log = 0;
21 uint32 value = n;
22 for (int i = 4; i >= 0; --i) {
23 int shift = (1 << i);
24 uint32 x = value >> shift;
25 if (x != 0) {
26 value = x;
27 log += shift;
28 }
29 }
30 DCHECK_EQ(value, 1u);
31 return log;
32}
33
34// Returns the integer i such as 2^(i-1) < n <= 2^i
35inline int Log2Ceiling(uint32 n) {
36 if (n == 0) {
37 return -1;
38 } else {
39 // Log2Floor returns -1 for 0, so the following works correctly for n=1.
40 return 1 + Log2Floor(n - 1);
41 }
42}
43
primiano47c69062015-07-25 05:13:32 +090044// Round up |size| to a multiple of alignment, which must be a power of two.
45inline size_t Align(size_t size, size_t alignment) {
46 DCHECK_EQ(alignment & (alignment - 1), 0u);
47 return (size + alignment - 1) & ~(alignment - 1);
48}
49
apatrick@google.com0265b732009-11-19 08:08:39 +090050} // namespace bits
51} // namespace base
52
53#endif // BASE_BITS_H_