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 <__assert>
13#include <__bit/countl.h>
14#include <__config>
15#include <__type_traits/integer_traits.h>
16#include <limits>
17
18#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
19#  pragma GCC system_header
20#endif
21
22_LIBCPP_BEGIN_NAMESPACE_STD
23
24template <class _Tp>
25_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp __bit_log2(_Tp __t) _NOEXCEPT {
26  static_assert(__is_unsigned_integer_v<_Tp>, "__bit_log2 requires an unsigned integer type");
27  _LIBCPP_ASSERT_INTERNAL(__t != 0, "logarithm of 0 is undefined");
28  return numeric_limits<_Tp>::digits - 1 - std::__countl_zero(__t);
29}
30
31_LIBCPP_END_NAMESPACE_STD
32
33#endif // _LIBCPP___BIT_BIT_LOG2_H