v1/__bit/bit_log2.h

0001 //===----------------------------------------------------------------------===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008
0009 #ifndef _LIBCPP___BIT_BIT_LOG2_H
0010 #define _LIBCPP___BIT_BIT_LOG2_H
0011
0012 #include <__bit/countl.h>
0013 #include <__config>
0014 #include <__type_traits/is_unsigned_integer.h>
0015 #include <limits>
0016
0017 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0018 #  pragma GCC system_header
0019 #endif
0020
0021 _LIBCPP_BEGIN_NAMESPACE_STD
0022
0023 #if _LIBCPP_STD_VER >= 14
0024
0025 template <class _Tp>
0026 _LIBCPP_HIDE_FROM_ABI constexpr _Tp __bit_log2(_Tp __t) noexcept {
0027   static_assert(__libcpp_is_unsigned_integer<_Tp>::value, "__bit_log2 requires an unsigned integer type");
0028   return numeric_limits<_Tp>::digits - 1 - std::__countl_zero(__t);
0029 }
0030
0031 #endif // _LIBCPP_STD_VER >= 14
0032
0033 _LIBCPP_END_NAMESPACE_STD
0034
0035 #endif // _LIBCPP___BIT_BIT_LOG2_H