48 lines
1004 B
C++
48 lines
1004 B
C++
// 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_
|