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 14 namespace base { 15 namespace bits { 16 17 // Returns the integer i such as 2^i <= n < 2^(i+1) 18 inline 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 36 inline 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
