34 lines
1.1 KiB
C++
34 lines
1.1 KiB
C++
// Copyright (c) 2013 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 THIRD_PARTY_BASE_BITS_H_
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#define THIRD_PARTY_BASE_BITS_H_
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#include <type_traits>
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namespace pdfium {
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namespace base {
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namespace bits {
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// TODO(thestig): When C++20 is required, replace with std::has_single_bit().
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// Returns true iff |value| is a power of 2.
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template <typename T, typename = std::enable_if<std::is_integral<T>::value>>
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constexpr inline bool IsPowerOfTwo(T value) {
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// From "Hacker's Delight": Section 2.1 Manipulating Rightmost Bits.
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//
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// Only positive integers with a single bit set are powers of two. If only one
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// bit is set in x (e.g. 0b00000100000000) then |x-1| will have that bit set
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// to zero and all bits to its right set to 1 (e.g. 0b00000011111111). Hence
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// |x & (x-1)| is 0 iff x is a power of two.
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return value > 0 && (value & (value - 1)) == 0;
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}
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} // namespace bits
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} // namespace base
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} // namespace pdfium
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#endif // THIRD_PARTY_BASE_BITS_H_
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