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#pragma once
10
11#include "base/basictypes.h"
12#include "base/logging.h"
13
14namespace base {
15namespace bits {
16
17// Returns the integer i such as 2^i <= n < 2^(i+1)
18inline int Log2Floor(uint32 n) {
19  if (n == 0)
20    return -1;
21  int log = 0;
22  uint32 value = n;
23  for (int i = 4; i >= 0; --i) {
24    int shift = (1 << i);
25    uint32 x = value >> shift;
26    if (x != 0) {
27      value = x;
28      log += shift;
29    }
30  }
31  DCHECK_EQ(value, 1u);
32  return log;
33}
34
35// Returns the integer i such as 2^(i-1) < n <= 2^i
36inline int Log2Ceiling(uint32 n) {
37  if (n == 0) {
38    return -1;
39  } else {
40    // Log2Floor returns -1 for 0, so the following works correctly for n=1.
41    return 1 + Log2Floor(n - 1);
42  }
43}
44
45}  // namespace bits
46}  // namespace base
47
48#endif  // BASE_BITS_H_
49