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 <stddef.h>
11 #include <stdint.h>
12 
13 #include "base/logging.h"
14 
15 namespace base {
16 namespace bits {
17 
18 // Returns the integer i such as 2^i <= n < 2^(i+1)
Log2Floor(uint32_t n)19 inline int Log2Floor(uint32_t n) {
20   if (n == 0)
21     return -1;
22   int log = 0;
23   uint32_t value = n;
24   for (int i = 4; i >= 0; --i) {
25     int shift = (1 << i);
26     uint32_t x = value >> shift;
27     if (x != 0) {
28       value = x;
29       log += shift;
30     }
31   }
32   DCHECK_EQ(value, 1u);
33   return log;
34 }
35 
36 // Returns the integer i such as 2^(i-1) < n <= 2^i
Log2Ceiling(uint32_t n)37 inline int Log2Ceiling(uint32_t n) {
38   if (n == 0) {
39     return -1;
40   } else {
41     // Log2Floor returns -1 for 0, so the following works correctly for n=1.
42     return 1 + Log2Floor(n - 1);
43   }
44 }
45 
46 // Round up |size| to a multiple of alignment, which must be a power of two.
Align(size_t size,size_t alignment)47 inline size_t Align(size_t size, size_t alignment) {
48   DCHECK_EQ(alignment & (alignment - 1), 0u);
49   return (size + alignment - 1) & ~(alignment - 1);
50 }
51 
52 }  // namespace bits
53 }  // namespace base
54 
55 #endif  // BASE_BITS_H_
56