apatrick@google.com | 0265b73 | 2009-11-19 08:08:39 +0900 | [diff] [blame] | 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_ |
apatrick@google.com | 0265b73 | 2009-11-19 08:08:39 +0900 | [diff] [blame] | 9 | |
| 10 | #include "base/basictypes.h" |
| 11 | #include "base/logging.h" |
| 12 | |
| 13 | namespace base { |
| 14 | namespace bits { |
| 15 | |
| 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; |
| 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 |
| 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); |
| 41 | } |
| 42 | } |
| 43 | |
| 44 | } // namespace bits |
| 45 | } // namespace base |
| 46 | |
| 47 | #endif // BASE_BITS_H_ |