48 lines
1004 B
C
48 lines
1004 B
C
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// Copyright (c) 2009 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// This file defines some bit utilities.
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#ifndef BASE_BITS_H_
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#define BASE_BITS_H_
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#include "base/basictypes.h"
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#include "base/logging.h"
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namespace base {
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namespace bits {
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// Returns the integer i such as 2^i <= n < 2^(i+1)
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inline int Log2Floor(uint32 n) {
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if (n == 0)
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return -1;
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int log = 0;
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uint32 value = n;
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for (int i = 4; i >= 0; --i) {
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int shift = (1 << i);
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uint32 x = value >> shift;
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if (x != 0) {
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value = x;
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log += shift;
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}
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}
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DCHECK_EQ(value, 1u);
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return log;
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}
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// Returns the integer i such as 2^(i-1) < n <= 2^i
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inline int Log2Ceiling(uint32 n) {
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if (n == 0) {
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return -1;
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} else {
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// Log2Floor returns -1 for 0, so the following works correctly for n=1.
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return 1 + Log2Floor(n - 1);
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}
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}
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} // namespace bits
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} // namespace base
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#endif // BASE_BITS_H_
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