fix chrome/utility lacking dependency on chrome_strings
[chromium-blink-merge.git] / base / bits.h
blobb2209e8ed7934a6dfc918c3d7d12b9c455f594e1
1 // 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.
5 // This file defines some bit utilities.
7 #ifndef BASE_BITS_H_
8 #define BASE_BITS_H_
10 #include "base/basictypes.h"
11 #include "base/logging.h"
13 namespace base {
14 namespace bits {
16 // Returns the integer i such as 2^i <= n < 2^(i+1)
17 inline 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;
30 DCHECK_EQ(value, 1u);
31 return log;
34 // Returns the integer i such as 2^(i-1) < n <= 2^i
35 inline 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);
44 } // namespace bits
45 } // namespace base
47 #endif // BASE_BITS_H_