libcxx/include/__cxx03/__bit/bit_log2.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___BIT_BIT_LOG2_H
  10 #define _LIBCPP___BIT_BIT_LOG2_H
  11
  12 #include <__cxx03/__bit/countl.h>
  13 #include <__cxx03/__concepts/arithmetic.h>
  14 #include <__cxx03/__config>
  15 #include <__cxx03/limits>
  16
  17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  18 #  pragma GCC system_header
  19 #endif
  20
  21 _LIBCPP_BEGIN_NAMESPACE_STD
  22
  23 #if _LIBCPP_STD_VER >= 20
  24
  25 template <__libcpp_unsigned_integer _Tp>
  26 _LIBCPP_HIDE_FROM_ABI constexpr _Tp __bit_log2(_Tp __t) noexcept {
  27   return numeric_limits<_Tp>::digits - 1 - std::countl_zero(__t);
  28 }
  29
  30 #endif // _LIBCPP_STD_VER >= 20
  31
  32 _LIBCPP_END_NAMESPACE_STD
  33
  34 #endif // _LIBCPP___BIT_BIT_LOG2_H