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.
4
5// This file defines some bit utilities.
6
7#ifndef BASE_BITS_H_
8#define BASE_BITS_H_
9
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
44}  // namespace bits
45}  // namespace base
46
47#endif  // BASE_BITS_H_
48