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 <__bit/rotate.h>
#include <__concepts/arithmetic.h>
#include <__config>
#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

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
int __libcpp_ctz(unsigned __x)           _NOEXCEPT { return __builtin_ctz(__x); }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
int __libcpp_ctz(unsigned long __x)      _NOEXCEPT { return __builtin_ctzl(__x); }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
int __libcpp_ctz(unsigned long long __x) _NOEXCEPT { return __builtin_ctzll(__x); }

#if _LIBCPP_STD_VER >= 20

template <__libcpp_unsigned_integer _Tp>
_LIBCPP_HIDE_FROM_ABI constexpr int countr_zero(_Tp __t) noexcept {
  if (__t == 0)
    return numeric_limits<_Tp>::digits;

  if (sizeof(_Tp) <= sizeof(unsigned int))
    return std::__libcpp_ctz(static_cast<unsigned int>(__t));
  else if (sizeof(_Tp) <= sizeof(unsigned long))
    return std::__libcpp_ctz(static_cast<unsigned long>(__t));
  else if (sizeof(_Tp) <= sizeof(unsigned long long))
    return std::__libcpp_ctz(static_cast<unsigned long long>(__t));
  else {
    int __ret = 0;
    const unsigned int __ulldigits = numeric_limits<unsigned long long>::digits;
    while (static_cast<unsigned long long>(__t) == 0uLL) {
      __ret += __ulldigits;
      __t >>= __ulldigits;
    }
    return __ret + std::__libcpp_ctz(static_cast<unsigned long long>(__t));
  }
}

template <__libcpp_unsigned_integer _Tp>
_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