libcxx/include/__bit/countr.h

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___BIT_COUNTR_H
#define _LIBCPP___BIT_COUNTR_H

#include <__concepts/arithmetic.h>
#include <__config>
#include <__type_traits/is_unsigned.h>
#include <limits>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_PUSH_MACROS
#include <__undef_macros>

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp>
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __countr_zero(_Tp __t) _NOEXCEPT {
  static_assert(is_unsigned<_Tp>::value, "__countr_zero only works with unsigned types");
  return __builtin_ctzg(__t, numeric_limits<_Tp>::digits);
}

#if _LIBCPP_STD_VER >= 20

template <__libcpp_unsigned_integer _Tp>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countr_zero(_Tp __t) noexcept {
  return std::__countr_zero(__t);
}

template <__libcpp_unsigned_integer _Tp>
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr int countr_one(_Tp __t) noexcept {
  return __t != numeric_limits<_Tp>::max() ? std::countr_zero(static_cast<_Tp>(~__t)) : numeric_limits<_Tp>::digits;
}

#endif // _LIBCPP_STD_VER >= 20

_LIBCPP_END_NAMESPACE_STD

_LIBCPP_POP_MACROS

#endif // _LIBCPP___BIT_COUNTR_H