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- // Copyright (c) 2009 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- // This file defines some bit utilities.
- #ifndef BASE_BITS_H_
- #define BASE_BITS_H_
- #include "base/basictypes.h"
- #include "base/logging.h"
- namespace base {
- namespace bits {
- // Returns the integer i such as 2^i <= n < 2^(i+1)
- inline int Log2Floor(uint32_t n) {
- if (n == 0)
- return -1;
- int log = 0;
- uint32_t value = n;
- for (int i = 4; i >= 0; --i) {
- int shift = (1 << i);
- uint32_t x = value >> shift;
- if (x != 0) {
- value = x;
- log += shift;
- }
- }
- DCHECK_EQ(value, 1u);
- return log;
- }
- // Returns the integer i such as 2^(i-1) < n <= 2^i
- inline int Log2Ceiling(uint32_t n) {
- if (n == 0) {
- return -1;
- } else {
- // Log2Floor returns -1 for 0, so the following works correctly for n=1.
- return 1 + Log2Floor(n - 1);
- }
- }
- } // namespace bits
- } // namespace base
- #endif // BASE_BITS_H_
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