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