274a4c0c03
Clang translates most implementations of has_single_bit to `(v ^ (v-1)) > v-1` - except the one definition libc++ actually uses. Proof of correctness: https://godbolt.org/z/d61bxW4r1 (Could also be fixed by teaching Clang to optimize better, but making source match output feels clearer to me. And it improves unoptimized performance.)
38 lines
985 B
C++
38 lines
985 B
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___BIT_HAS_SINGLE_BIT_H
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#define _LIBCPP___BIT_HAS_SINGLE_BIT_H
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#include <__config>
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#include <__type_traits/integer_traits.h>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_PUSH_MACROS
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#include <__undef_macros>
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#if _LIBCPP_STD_VER >= 20
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <__unsigned_integer _Tp>
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[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool has_single_bit(_Tp __t) noexcept {
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return __builtin_popcountg(__t) == 1;
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}
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP_STD_VER >= 20
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_LIBCPP_POP_MACROS
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#endif // _LIBCPP___BIT_HAS_SINGLE_BIT_H
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