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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 n) {
if (n == 0)
return -1;
int log = 0;
uint32 value = n;
for (int i = 4; i >= 0; --i) {
int shift = (1 << i);
uint32 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 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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