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 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_ 48
